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Posted to commits@zookeeper.apache.org by eo...@apache.org on 2022/01/27 09:07:08 UTC

[zookeeper] branch master updated: ZOOKEEPER-4427: Migrate to Logback

This is an automated email from the ASF dual-hosted git repository.

eolivelli pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/zookeeper.git


The following commit(s) were added to refs/heads/master by this push:
     new 85551f9  ZOOKEEPER-4427: Migrate to Logback
85551f9 is described below

commit 85551f9be5b054fa4aee0636597b12bda2ecb2e8
Author: Andor Molnar <an...@apache.org>
AuthorDate: Thu Jan 27 10:06:29 2022 +0100

    ZOOKEEPER-4427: Migrate to Logback
    
    This is the first commit of Logback migration task.
    
    1. Replaced log4j dependencies with logback alternatives,
    2. Replaced log4j.properties files with logback.xml
    3. Refactored unit tests to use logback for log capturing.
    
    This patch doesn't cover the zookeeper-contrib projects, only the main codebase.
    
    Author: Andor Molnar <an...@apache.org>
    
    Reviewers: Enrico Olivelli <eo...@apache.org>, Chris Nauroth <cn...@apache.org>, Mate Szalay-Beko <sy...@apache.org>
    
    Closes #1793 from anmolnar/ZOOKEEPER-4427
---
 bin/zkCleanup.sh                                   |   4 +-
 bin/zkCli.cmd                                      |   2 +-
 bin/zkCli.sh                                       |   2 +-
 bin/zkEnv.cmd                                      |   1 -
 bin/zkEnv.sh                                       |   5 -
 bin/zkServer.cmd                                   |   2 +-
 bin/zkServer.sh                                    |   8 +-
 conf/log4j.properties                              |  82 ----
 conf/logback.xml                                   | 114 ++++++
 owaspSuppressions.xml                              |  10 -
 pom.xml                                            |  11 +
 .../src/main/resources/markdown/zookeeperAdmin.md  |  40 +-
 .../main/resources/markdown/zookeeperAuditLogs.md  |  49 ++-
 .../main/resources/markdown/zookeeperInternals.md  |   9 +-
 .../src/main/resources/markdown/zookeeperJMX.md    |  13 +-
 .../main/resources/markdown/zookeeperStarted.md    |   9 +-
 .../src/main/resources/markdown/zookeeperTools.md  |   3 +-
 .../src/test/resources/log4j.properties            |  65 ----
 .../src/test/resources/logback.xml                 |  36 ++
 zookeeper-server/pom.xml                           |  12 +-
 ...Log4jAuditLogger.java => Slf4jAuditLogger.java} |   6 +-
 .../apache/zookeeper/audit/ZKAuditProvider.java    |   2 +-
 .../java/org/apache/zookeeper/server/ZooTrace.java |   2 +-
 zookeeper-server/src/main/resources/NOTICE.txt     |   6 +-
 .../main/resources/lib/log4j-1.2.17.LICENSE.txt    | 202 ----------
 .../lib/logback-classic-1.2.10.LICENSE.txt         | 414 +++++++++++++++++++++
 .../resources/lib/logback-core-1.2.10.LICENSE.txt  | 414 +++++++++++++++++++++
 ...itLoggerTest.java => Slf4JAuditLoggerTest.java} |  35 +-
 .../zookeeper/audit/StandaloneServerAuditTest.java |  19 +-
 .../server/quorum/QuorumPeerMainTest.java          | 382 ++++++++-----------
 .../org/apache/zookeeper/test/LoggerTestTool.java  |  88 +++++
 .../apache/zookeeper/test/ReadOnlyModeTest.java    |  43 +--
 .../zookeeper/test/ReconfigExceptionTest.java      |   4 +-
 .../src/test/resources/log4j.properties            |  65 ----
 zookeeper-server/src/test/resources/logback.xml    |  36 ++
 35 files changed, 1381 insertions(+), 814 deletions(-)

diff --git a/bin/zkCleanup.sh b/bin/zkCleanup.sh
index 4553241..b6fe0e7 100755
--- a/bin/zkCleanup.sh
+++ b/bin/zkCleanup.sh
@@ -43,11 +43,11 @@ ZOO_LOG_FILE=zookeeper-$USER-cleanup-$HOSTNAME.log
 
 if [ "x$ZOODATALOGDIR" = "x" ]
 then
-"$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
+"$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
      -cp "$CLASSPATH" $JVMFLAGS \
      org.apache.zookeeper.server.PurgeTxnLog "$ZOODATADIR" $*
 else
-"$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
+"$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
      -cp "$CLASSPATH" $JVMFLAGS \
      org.apache.zookeeper.server.PurgeTxnLog "$ZOODATALOGDIR" "$ZOODATADIR" $*
 fi
diff --git a/bin/zkCli.cmd b/bin/zkCli.cmd
index 807ffaa..7a4391d 100644
--- a/bin/zkCli.cmd
+++ b/bin/zkCli.cmd
@@ -20,7 +20,7 @@ call "%~dp0zkEnv.cmd"
 set ZOO_LOG_FILE=zookeeper-%USERNAME%-cli-%COMPUTERNAME%.log
 
 set ZOOMAIN=org.apache.zookeeper.ZooKeeperMain
-call %JAVA% "-Dzookeeper.log.dir=%ZOO_LOG_DIR%" "-Dzookeeper.root.logger=%ZOO_LOG4J_PROP%" "-Dzookeeper.log.file=%ZOO_LOG_FILE%" -cp "%CLASSPATH%" %ZOOMAIN% %*
+call %JAVA% "-Dzookeeper.log.dir=%ZOO_LOG_DIR%" "-Dzookeeper.log.file=%ZOO_LOG_FILE%" -cp "%CLASSPATH%" %ZOOMAIN% %*
 
 endlocal
 
diff --git a/bin/zkCli.sh b/bin/zkCli.sh
index ecf9a45..3810e7f 100755
--- a/bin/zkCli.sh
+++ b/bin/zkCli.sh
@@ -38,6 +38,6 @@ fi
 
 ZOO_LOG_FILE=zookeeper-$USER-cli-$HOSTNAME.log
 
-"$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
+"$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
      -cp "$CLASSPATH" $CLIENT_JVMFLAGS $JVMFLAGS \
      org.apache.zookeeper.ZooKeeperMain "$@"
diff --git a/bin/zkEnv.cmd b/bin/zkEnv.cmd
index 68e231d..de9fc92 100644
--- a/bin/zkEnv.cmd
+++ b/bin/zkEnv.cmd
@@ -16,7 +16,6 @@ REM limitations under the License.
 
 set ZOOCFGDIR=%~dp0%..\conf
 set ZOO_LOG_DIR=%~dp0%..\logs
-set ZOO_LOG4J_PROP=INFO,CONSOLE
 
 REM for sanity sake assume Java 1.6
 REM see: http://java.sun.com/javase/6/docs/technotes/tools/windows/java.html
diff --git a/bin/zkEnv.sh b/bin/zkEnv.sh
index 8d93a50..0728c2e 100755
--- a/bin/zkEnv.sh
+++ b/bin/zkEnv.sh
@@ -70,11 +70,6 @@ then
     ZOO_LOG_DIR="$ZOOKEEPER_PREFIX/logs"
 fi
 
-if [ "x${ZOO_LOG4J_PROP}" = "x" ]
-then
-    ZOO_LOG4J_PROP="INFO,CONSOLE"
-fi
-
 if [[ -n "$JAVA_HOME" ]] && [[ -x "$JAVA_HOME/bin/java" ]];  then
     JAVA="$JAVA_HOME/bin/java"
 elif type -p java; then
diff --git a/bin/zkServer.cmd b/bin/zkServer.cmd
index b03a443..07ac3a3 100644
--- a/bin/zkServer.cmd
+++ b/bin/zkServer.cmd
@@ -21,6 +21,6 @@ set ZOOMAIN=org.apache.zookeeper.server.quorum.QuorumPeerMain
 set ZOO_LOG_FILE=zookeeper-%USERNAME%-server-%COMPUTERNAME%.log
 
 echo on
-call %JAVA% "-Dzookeeper.log.dir=%ZOO_LOG_DIR%" "-Dzookeeper.root.logger=%ZOO_LOG4J_PROP%" "-Dzookeeper.log.file=%ZOO_LOG_FILE%" "-XX:+HeapDumpOnOutOfMemoryError" "-XX:OnOutOfMemoryError=cmd /c taskkill /pid %%%%p /t /f" -cp "%CLASSPATH%" %ZOOMAIN% "%ZOOCFG%" %*
+call %JAVA% "-Dzookeeper.log.dir=%ZOO_LOG_DIR%" "-Dzookeeper.log.file=%ZOO_LOG_FILE%" "-XX:+HeapDumpOnOutOfMemoryError" "-XX:OnOutOfMemoryError=cmd /c taskkill /pid %%%%p /t /f" -cp "%CLASSPATH%" %ZOOMAIN% "%ZOOCFG%" %*
 
 endlocal
diff --git a/bin/zkServer.sh b/bin/zkServer.sh
index 1a3cd35..977c1bb 100755
--- a/bin/zkServer.sh
+++ b/bin/zkServer.sh
@@ -162,7 +162,7 @@ start)
       fi
     fi
     nohup "$JAVA" $ZOO_DATADIR_AUTOCREATE "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" \
-    "-Dzookeeper.log.file=${ZOO_LOG_FILE}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" \
+    "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
     -XX:+HeapDumpOnOutOfMemoryError -XX:OnOutOfMemoryError='kill -9 %p' \
     -cp "$CLASSPATH" $JVMFLAGS $ZOOMAIN "$ZOOCFG" > "$_ZOO_DAEMON_OUT" 2>&1 < /dev/null &
     if [ $? -eq 0 ]
@@ -200,13 +200,13 @@ start-foreground)
       ZOO_CMD=("$JAVA")
     fi
     "${ZOO_CMD[@]}" $ZOO_DATADIR_AUTOCREATE "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" \
-    "-Dzookeeper.log.file=${ZOO_LOG_FILE}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" \
+    "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
     -XX:+HeapDumpOnOutOfMemoryError -XX:OnOutOfMemoryError='kill -9 %p' \
     -cp "$CLASSPATH" $JVMFLAGS $ZOOMAIN "$ZOOCFG"
     ;;
 print-cmd)
     echo "\"$JAVA\" $ZOO_DATADIR_AUTOCREATE -Dzookeeper.log.dir=\"${ZOO_LOG_DIR}\" \
-    -Dzookeeper.log.file=\"${ZOO_LOG_FILE}\" -Dzookeeper.root.logger=\"${ZOO_LOG4J_PROP}\" \
+    -Dzookeeper.log.file=\"${ZOO_LOG_FILE}\" \
     -XX:+HeapDumpOnOutOfMemoryError -XX:OnOutOfMemoryError='kill -9 %p' \
     -cp \"$CLASSPATH\" $JVMFLAGS $ZOOMAIN \"$ZOOCFG\" > \"$_ZOO_DAEMON_OUT\" 2>&1 < /dev/null"
     ;;
@@ -287,7 +287,7 @@ status)
       fi
     fi
     echo "Client port found: $clientPort. Client address: $clientPortAddress. Client SSL: $isSSL."
-    STAT=`"$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
+    STAT=`"$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
           -cp "$CLASSPATH" $CLIENT_JVMFLAGS $JVMFLAGS org.apache.zookeeper.client.FourLetterWordMain \
           $clientPortAddress $clientPort srvr $isSSL 2> /dev/null    \
           | $GREP Mode`
diff --git a/conf/log4j.properties b/conf/log4j.properties
deleted file mode 100644
index 9e12a38..0000000
--- a/conf/log4j.properties
+++ /dev/null
@@ -1,82 +0,0 @@
-# Copyright 2012 The Apache Software Foundation
-# 
-# Licensed to the Apache Software Foundation (ASF) under one
-# or more contributor license agreements.  See the NOTICE file
-# distributed with this work for additional information
-# regarding copyright ownership.  The ASF licenses this file
-# to you under the Apache License, Version 2.0 (the
-# "License"); you may not use this file except in compliance
-# with the License.  You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-# Define some default values that can be overridden by system properties
-zookeeper.root.logger=INFO, CONSOLE
-
-zookeeper.console.threshold=INFO
-
-zookeeper.log.dir=.
-zookeeper.log.file=zookeeper.log
-zookeeper.log.threshold=INFO
-zookeeper.log.maxfilesize=256MB
-zookeeper.log.maxbackupindex=20
-
-zookeeper.tracelog.dir=${zookeeper.log.dir}
-zookeeper.tracelog.file=zookeeper_trace.log
-
-log4j.rootLogger=${zookeeper.root.logger}
-
-#
-# console
-# Add "console" to rootlogger above if you want to use this 
-#
-log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
-log4j.appender.CONSOLE.Threshold=${zookeeper.console.threshold}
-log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
-log4j.appender.CONSOLE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n
-
-#
-# Add ROLLINGFILE to rootLogger to get log file output
-#
-log4j.appender.ROLLINGFILE=org.apache.log4j.RollingFileAppender
-log4j.appender.ROLLINGFILE.Threshold=${zookeeper.log.threshold}
-log4j.appender.ROLLINGFILE.File=${zookeeper.log.dir}/${zookeeper.log.file}
-log4j.appender.ROLLINGFILE.MaxFileSize=${zookeeper.log.maxfilesize}
-log4j.appender.ROLLINGFILE.MaxBackupIndex=${zookeeper.log.maxbackupindex}
-log4j.appender.ROLLINGFILE.layout=org.apache.log4j.PatternLayout
-log4j.appender.ROLLINGFILE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n
-
-#
-# Add TRACEFILE to rootLogger to get log file output
-#    Log TRACE level and above messages to a log file
-#
-log4j.appender.TRACEFILE=org.apache.log4j.FileAppender
-log4j.appender.TRACEFILE.Threshold=TRACE
-log4j.appender.TRACEFILE.File=${zookeeper.tracelog.dir}/${zookeeper.tracelog.file}
-
-log4j.appender.TRACEFILE.layout=org.apache.log4j.PatternLayout
-### Notice we are including log4j's NDC here (%x)
-log4j.appender.TRACEFILE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L][%x] - %m%n
-#
-# zk audit logging
-#
-zookeeper.auditlog.file=zookeeper_audit.log
-zookeeper.auditlog.threshold=INFO
-audit.logger=INFO, RFAAUDIT
-log4j.logger.org.apache.zookeeper.audit.Log4jAuditLogger=${audit.logger}
-log4j.additivity.org.apache.zookeeper.audit.Log4jAuditLogger=false
-log4j.appender.RFAAUDIT=org.apache.log4j.RollingFileAppender
-log4j.appender.RFAAUDIT.File=${zookeeper.log.dir}/${zookeeper.auditlog.file}
-log4j.appender.RFAAUDIT.layout=org.apache.log4j.PatternLayout
-log4j.appender.RFAAUDIT.layout.ConversionPattern=%d{ISO8601} %p %c{2}: %m%n
-log4j.appender.RFAAUDIT.Threshold=${zookeeper.auditlog.threshold}
-
-# Max log file size of 10MB
-log4j.appender.RFAAUDIT.MaxFileSize=10MB
-log4j.appender.RFAAUDIT.MaxBackupIndex=10
diff --git a/conf/logback.xml b/conf/logback.xml
new file mode 100644
index 0000000..84a5389
--- /dev/null
+++ b/conf/logback.xml
@@ -0,0 +1,114 @@
+<!--
+ Copyright 2022 The Apache Software Foundation
+
+ Licensed to the Apache Software Foundation (ASF) under one
+ or more contributor license agreements.  See the NOTICE file
+ distributed with this work for additional information
+ regarding copyright ownership.  The ASF licenses this file
+ to you under the Apache License, Version 2.0 (the
+ "License"); you may not use this file except in compliance
+ with the License.  You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+
+ Define some default values that can be overridden by system properties
+-->
+<configuration>
+  <!-- Uncomment this if you would like to expose Logback JMX beans -->
+  <!--jmxConfigurator /-->
+
+  <property name="zookeeper.console.threshold" value="INFO" />
+
+  <property name="zookeeper.log.dir" value="." />
+  <property name="zookeeper.log.file" value="zookeeper.log" />
+  <property name="zookeeper.log.threshold" value="INFO" />
+  <property name="zookeeper.log.maxfilesize" value="256MB" />
+  <property name="zookeeper.log.maxbackupindex" value="20" />
+
+  <!--
+    console
+    Add "console" to root logger if you want to use this
+  -->
+  <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
+    <encoder>
+      <pattern>%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n</pattern>
+    </encoder>
+    <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
+      <level>${zookeeper.console.threshold}</level>
+    </filter>
+  </appender>
+
+  <!--
+    Add ROLLINGFILE to root logger to get log file output
+  -->
+  <!--appender name="ROLLINGFILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
+    <File>${zookeeper.log.dir}/${zookeeper.log.file}</File>
+    <encoder>
+      <pattern>%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n</pattern>
+    </encoder>
+    <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
+      <level>${zookeeper.log.threshold}</level>
+    </filter>
+    <rollingPolicy class="ch.qos.logback.core.rolling.FixedWindowRollingPolicy">
+      <maxIndex>${zookeeper.log.maxbackupindex}</maxIndex>
+      <FileNamePattern>${zookeeper.log.dir}/${zookeeper.log.file}.%i</FileNamePattern>
+    </rollingPolicy>
+    <triggeringPolicy class="ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy">
+      <MaxFileSize>${zookeeper.log.maxfilesize}</MaxFileSize>
+    </triggeringPolicy>
+  </appender-->
+
+  <!--
+    Add TRACEFILE to root logger to get log file output
+    Log TRACE level and above messages to a log file
+  -->
+  <!--property name="zookeeper.tracelog.dir" value="${zookeeper.log.dir}" />
+  <property name="zookeeper.tracelog.file" value="zookeeper_trace.log" />
+  <appender name="TRACEFILE" class="ch.qos.logback.core.FileAppender">
+    <File>${zookeeper.tracelog.dir}/${zookeeper.tracelog.file}</File>
+    <encoder>
+      <pattern>%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n</pattern>
+    </encoder>
+    <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
+      <level>TRACE</level>
+    </filter>
+  </appender-->
+
+  <!--
+    zk audit logging
+  -->
+  <!--property name="zookeeper.auditlog.file" value="zookeeper_audit.log" />
+  <property name="zookeeper.auditlog.threshold" value="INFO" />
+  <property name="audit.logger" value="INFO, RFAAUDIT" />
+
+  <appender name="RFAAUDIT" class="ch.qos.logback.core.rolling.RollingFileAppender">
+    <File>${zookeeper.log.dir}/${zookeeper.auditlog.file}</File>
+    <encoder>
+      <pattern>%d{ISO8601} %p %c{2}: %m%n</pattern>
+    </encoder>
+    <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
+      <level>${zookeeper.auditlog.threshold}</level>
+    </filter>
+    <rollingPolicy class="ch.qos.logback.core.rolling.FixedWindowRollingPolicy">
+      <maxIndex>10</maxIndex>
+      <FileNamePattern>${zookeeper.log.dir}/${zookeeper.auditlog.file}.%i</FileNamePattern>
+    </rollingPolicy>
+    <triggeringPolicy class="ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy">
+      <MaxFileSize>10MB</MaxFileSize>
+    </triggeringPolicy>
+  </appender>
+
+  <logger name="org.apache.zookeeper.audit.Slf4jAuditLogger" additivity="false" level="${audit.logger}">
+    <appender-ref ref="RFAAUDIT" />
+  </logger-->
+
+  <root level="INFO">
+    <appender-ref ref="CONSOLE" />
+  </root>
+</configuration>
diff --git a/owaspSuppressions.xml b/owaspSuppressions.xml
index 2565f0d..5c4bc33 100644
--- a/owaspSuppressions.xml
+++ b/owaspSuppressions.xml
@@ -41,14 +41,4 @@
            this writing  -->
       <cve>CVE-2019-3826</cve>
    </suppress>
-   <suppress>
-      <!-- false positive for us, it is about log4j server in log4j-1.2.17.jar
-           ZOOKEEPER-3677 -->
-      <cve>CVE-2019-17571</cve>
-   </suppress>
-   <suppress>
-      <!-- it only affects the log4j SmtpAppender users. As Log4J 1.2 is EOL now, we can't fix this unless we
-           upgrade to log4j 2. See ZOOKEEPER-3817 -->
-      <cve>CVE-2020-9488</cve>
-   </suppress>
 </suppressions>
diff --git a/pom.xml b/pom.xml
index de2e44d..646637c 100755
--- a/pom.xml
+++ b/pom.xml
@@ -459,6 +459,7 @@
 
     <!-- dependency versions -->
     <slf4j.version>1.7.30</slf4j.version>
+    <logback-version>1.2.10</logback-version>
     <audience-annotations.version>0.12.0</audience-annotations.version>
     <jmockit.version>1.48</jmockit.version>
     <junit.version>5.6.2</junit.version>
@@ -578,6 +579,16 @@
         <version>${log4j.version}</version>
       </dependency>
       <dependency>
+        <groupId>ch.qos.logback</groupId>
+        <artifactId>logback-core</artifactId>
+        <version>${logback-version}</version>
+      </dependency>
+      <dependency>
+        <groupId>ch.qos.logback</groupId>
+        <artifactId>logback-classic</artifactId>
+        <version>${logback-version}</version>
+      </dependency>
+      <dependency>
         <groupId>org.jmockit</groupId>
         <artifactId>jmockit</artifactId>
         <version>${jmockit.version}</version>
diff --git a/zookeeper-docs/src/main/resources/markdown/zookeeperAdmin.md b/zookeeper-docs/src/main/resources/markdown/zookeeperAdmin.md
index 84ecf94..eaefdda 100644
--- a/zookeeper-docs/src/main/resources/markdown/zookeeperAdmin.md
+++ b/zookeeper-docs/src/main/resources/markdown/zookeeperAdmin.md
@@ -1,5 +1,5 @@
 <!--
-Copyright 2002-2004 The Apache Software Foundation
+Copyright 2002-2022 The Apache Software Foundation
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -33,7 +33,7 @@ limitations under the License.
     * [Administering](#sc_administering)
     * [Maintenance](#sc_maintenance)
         * [Ongoing Data Directory Cleanup](#Ongoing+Data+Directory+Cleanup)
-        * [Debug Log Cleanup (log4j)](#Debug+Log+Cleanup+%28log4j%29)
+        * [Debug Log Cleanup (logback)](#Debug+Log+Cleanup+Logback)
     * [Supervision](#sc_supervision)
     * [Monitoring](#sc_monitoring)
     * [Logging](#sc_logging)
@@ -436,7 +436,7 @@ in the unlikely event a recent log has become corrupted). This
 can be run as a cron job on the ZooKeeper server machines to
 clean up the logs daily.
 
-    java -cp zookeeper.jar:lib/slf4j-api-1.7.5.jar:lib/slf4j-log4j12-1.7.5.jar:lib/log4j-1.2.17.jar:conf org.apache.zookeeper.server.PurgeTxnLog <dataDir> <snapDir> -n <count>
+    java -cp zookeeper.jar:lib/slf4j-api-1.7.30.jar:lib/logback-classic-1.2.10.jar:lib/logback-core-1.2.10.jar:conf org.apache.zookeeper.server.PurgeTxnLog <dataDir> <snapDir> -n <count>
 
 
 Automatic purging of the snapshots and corresponding
@@ -445,14 +445,14 @@ enabled via the following configuration parameters **autopurge.snapRetainCount**
 this, see [Advanced Configuration](#sc_advancedConfiguration)
 below.
 
-<a name="Debug+Log+Cleanup+%28log4j%29"></a>
+<a name="Debug+Log+Cleanup+Logback"></a>
 
-#### Debug Log Cleanup (log4j)
+#### Debug Log Cleanup (logback)
 
 See the section on [logging](#sc_logging) in this document. It is
 expected that you will setup a rolling file appender using the
-in-built log4j feature. The sample configuration file in the
-release tar's conf/log4j.properties provides an example of
+in-built logback feature. The sample configuration file in the
+release tar's `conf/logback.xml` provides an example of
 this.
 
 <a name="sc_supervision"></a>
@@ -504,22 +504,20 @@ The ZooKeeper service can be monitored in one of three primary ways:
 ### Logging
 
 ZooKeeper uses **[SLF4J](http://www.slf4j.org)**
-version 1.7.5 as its logging infrastructure. For backward compatibility it is bound to
-**LOG4J** but you can use
-**[LOGBack](http://logback.qos.ch/)**
-or any other supported logging framework of your choice.
-
-The ZooKeeper default *log4j.properties*
-file resides in the *conf* directory. Log4j requires that
-*log4j.properties* either be in the working directory
+version 1.7 as its logging infrastructure. By default ZooKeeper is shipped with
+**[LOGBack](http://logback.qos.ch/)** as the logging backend, but you can use
+any other supported logging framework of your choice.
+
+The ZooKeeper default *logback.xml*
+file resides in the *conf* directory. Logback requires that
+*logback.xml* either be in the working directory
 (the directory from which ZooKeeper is run) or be accessible from the classpath.
 
 For more information about SLF4J, see
 [its manual](http://www.slf4j.org/manual.html).
 
-For more information about LOG4J, see
-[Log4j Default Initialization Procedure](http://logging.apache.org/log4j/1.2/manual.html#defaultInit)
-of the log4j manual.
+For more information about Logback, see
+[Logback website](http://logback.qos.ch/).
 
 <a name="sc_troubleshooting"></a>
 
@@ -1141,8 +1139,8 @@ property, when available, is noted below.
 * *audit.impl.class* :
     (Java system property: **zookeeper.audit.impl.class**)
     **New in 3.6.0:**
-    Class to implement the audit logger. By default log4j based audit logger org.apache.zookeeper.audit
-    .Log4jAuditLogger is used.
+    Class to implement the audit logger. By default logback based audit logger org.apache.zookeeper.audit
+    .Slf4jAuditLogger is used.
     See the [ZooKeeper audit logs](zookeeperAuditLogs.html) for more information.
 
 * *largeRequestMaxBytes* :
@@ -2427,7 +2425,7 @@ The output contains multiple lines with the following format:
 * *stmk* :
     Sets the current trace mask.  The trace mask is 64 bits,
     where each bit enables or disables a specific category of trace
-    logging on the server.  Log4J must be configured to enable
+    logging on the server. Logback must be configured to enable
     `TRACE` level first in order to see trace logging
     messages.  The bits of the trace mask correspond to the following
     trace logging categories.
diff --git a/zookeeper-docs/src/main/resources/markdown/zookeeperAuditLogs.md b/zookeeper-docs/src/main/resources/markdown/zookeeperAuditLogs.md
index 957980d..b3954ad 100644
--- a/zookeeper-docs/src/main/resources/markdown/zookeeperAuditLogs.md
+++ b/zookeeper-docs/src/main/resources/markdown/zookeeperAuditLogs.md
@@ -1,5 +1,5 @@
 <!--
-Copyright 2002-2004 The Apache Software Foundation
+Copyright 2002-2022 The Apache Software Foundation
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -66,25 +66,36 @@ Below are sample audit logs for all operations, where client is connected from 1
 
 ## ZooKeeper Audit Log Configuration
 
-By default audit logs are disabled. To enable audit logs configure audit.enable=true in conf/zoo.cfg. Audit logging is done using log4j. Following is the default log4j configuration for audit logs in conf/log4j.properties
-
-    #
-    # zk audit logging
-    #
-    zookeeper.auditlog.file=zookeeper_audit.log
-    zookeeper.auditlog.threshold=INFO
-    audit.logger=INFO, RFAAUDIT
-    log4j.logger.org.apache.zookeeper.audit.Log4jAuditLogger=${audit.logger}
-    log4j.additivity.org.apache.zookeeper.audit.Log4jAuditLogger=false
-    log4j.appender.RFAAUDIT=org.apache.log4j.RollingFileAppender
-    log4j.appender.RFAAUDIT.File=${zookeeper.log.dir}/${zookeeper.auditlog.file}
-    log4j.appender.RFAAUDIT.layout=org.apache.log4j.PatternLayout
-    log4j.appender.RFAAUDIT.layout.ConversionPattern=%d{ISO8601} %p %c{2}: %m%n
-    log4j.appender.RFAAUDIT.Threshold=${zookeeper.auditlog.threshold}
+By default audit logs are disabled. To enable audit logs configure `audit.enable=true` in _conf/zoo.cfg_. 
+Audit logging is done using logback. Following is the default logback configuration for audit logs in `conf/logback.xml`
+
+    <!--
+      zk audit logging
+    -->
+    <!--property name="zookeeper.auditlog.file" value="zookeeper_audit.log" />
+    <property name="zookeeper.auditlog.threshold" value="INFO" />
+    <property name="audit.logger" value="INFO, RFAAUDIT" />
+    
+    <appender name="RFAAUDIT" class="ch.qos.logback.core.rolling.RollingFileAppender">
+      <File>${zookeeper.log.dir}/${zookeeper.auditlog.file}</File>
+      <encoder>
+        <pattern>%d{ISO8601} %p %c{2}: %m%n</pattern>
+      </encoder>
+      <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
+        <level>${zookeeper.auditlog.threshold}</level>
+      </filter>
+      <rollingPolicy class="ch.qos.logback.core.rolling.FixedWindowRollingPolicy">
+        <maxIndex>10</maxIndex>
+        <FileNamePattern>${zookeeper.log.dir}/${zookeeper.auditlog.file}.%i</FileNamePattern>
+      </rollingPolicy>
+      <triggeringPolicy class="ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy">
+        <MaxFileSize>10MB</MaxFileSize>
+      </triggeringPolicy>
+    </appender>
     
-    # Max log file size of 10MB
-    log4j.appender.RFAAUDIT.MaxFileSize=10MB
-    log4j.appender.RFAAUDIT.MaxBackupIndex=10
+    <logger name="org.apache.zookeeper.audit.Slf4jAuditLogger" additivity="false" level="${audit.logger}">
+      <appender-ref ref="RFAAUDIT" />
+    </logger-->
 
 Change above configuration to customize the auditlog file, number of backups, max file size, custom audit logger etc.
 
diff --git a/zookeeper-docs/src/main/resources/markdown/zookeeperInternals.md b/zookeeper-docs/src/main/resources/markdown/zookeeperInternals.md
index 0505807..171f33d 100644
--- a/zookeeper-docs/src/main/resources/markdown/zookeeperInternals.md
+++ b/zookeeper-docs/src/main/resources/markdown/zookeeperInternals.md
@@ -1,5 +1,5 @@
 <!--
-Copyright 2002-2004 The Apache Software Foundation
+Copyright 2002-2022 The Apache Software Foundation
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -312,11 +312,12 @@ hierarchy of groups.
 
 ## Logging
 
-Zookeeper uses [slf4j](http://www.slf4j.org/index.html) as an abstraction layer for logging. [log4j](http://logging.apache.org/log4j) in version 1.2 is chosen as the final logging implementation for now.
+Zookeeper uses [slf4j](http://www.slf4j.org/index.html) as an abstraction layer for logging. 
+[Logback](https://logback.qos.ch/) is chosen the logging backend since ZooKeeper version 3.8.0.
 For better embedding support, it is planned in the future to leave the decision of choosing the final logging implementation to the end user.
-Therefore, always use the slf4j api to write log statements in the code, but configure log4j for how to log at runtime.
+Therefore, always use the slf4j api to write log statements in the code, but configure logback for how to log at runtime.
 Note that slf4j has no FATAL level, former messages at FATAL level have been moved to ERROR level.
-For information on configuring log4j for
+For information on configuring logback for
 ZooKeeper, see the [Logging](zookeeperAdmin.html#sc_logging) section
 of the [ZooKeeper Administrator's Guide.](zookeeperAdmin.html)
 
diff --git a/zookeeper-docs/src/main/resources/markdown/zookeeperJMX.md b/zookeeper-docs/src/main/resources/markdown/zookeeperJMX.md
index 368540f..99b366f 100644
--- a/zookeeper-docs/src/main/resources/markdown/zookeeperJMX.md
+++ b/zookeeper-docs/src/main/resources/markdown/zookeeperJMX.md
@@ -1,5 +1,5 @@
 <!--
-Copyright 2002-2004 The Apache Software Foundation
+Copyright 2002-2022 The Apache Software Foundation
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -77,8 +77,17 @@ on the left hand side. Expand this item and depending on how you've
 started the server you will be able to monitor and manage various
 service related features.
 
+#### Logback MBeans registration _(new in 3.8.0)_
+
+Logback is the default logging backend of ZooKeeper since version 3.8.0. 
+It can be configured to register JMX MBeans by adding `<jmxConfigurator />` to _logback.xml_. More
+information can be found on Logback's [website](https://logback.qos.ch/manual/jmxConfig.html).
+
+#### Log4j MBeans _(deprecated)_
+
 Also note that ZooKeeper will register log4j MBeans as
-well. In the same section along the left hand side you will see
+well if log4j1 is configured as the logging backend of SLF4j. 
+In the same section along the left hand side you will see
 "log4j". Expand that to manage log4j through JMX. Of particular
 interest is the ability to dynamically change the logging levels
 used by editing the appender and root thresholds. Log4j MBean
diff --git a/zookeeper-docs/src/main/resources/markdown/zookeeperStarted.md b/zookeeper-docs/src/main/resources/markdown/zookeeperStarted.md
index bb1e2f0..e44aae8 100644
--- a/zookeeper-docs/src/main/resources/markdown/zookeeperStarted.md
+++ b/zookeeper-docs/src/main/resources/markdown/zookeeperStarted.md
@@ -1,5 +1,5 @@
 <!--
-Copyright 2002-2004 The Apache Software Foundation
+Copyright 2002-2022 The Apache Software Foundation
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -101,12 +101,12 @@ ZooKeeper:
     bin/zkServer.sh start
 
 
-ZooKeeper logs messages using log4j -- more detail
+ZooKeeper logs messages using _logback_ -- more detail
 available in the
 [Logging](zookeeperProgrammers.html#Logging)
 section of the Programmer's Guide. You will see log messages
 coming to the console (default) and/or a log file depending on
-the log4j configuration.
+the logback configuration.
 
 The steps outlined here run ZooKeeper in standalone mode. There is
 no replication, so if ZooKeeper process fails, the service will go down.
@@ -137,8 +137,7 @@ Once you have connected, you should see something like:
 
 
     Connecting to localhost:2181
-    log4j:WARN No appenders could be found for logger (org.apache.zookeeper.ZooKeeper).
-    log4j:WARN Please initialize the log4j system properly.
+    ...
     Welcome to ZooKeeper!
     JLine support is enabled
     [zkshell: 0]
diff --git a/zookeeper-docs/src/main/resources/markdown/zookeeperTools.md b/zookeeper-docs/src/main/resources/markdown/zookeeperTools.md
index cd8b441..5141766 100644
--- a/zookeeper-docs/src/main/resources/markdown/zookeeperTools.md
+++ b/zookeeper-docs/src/main/resources/markdown/zookeeperTools.md
@@ -1,5 +1,5 @@
 <!--
-Copyright 2002-2021 The Apache Software Foundation
+Copyright 2002-2022 The Apache Software Foundation
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -96,7 +96,6 @@ The environment setting for the ZooKeeper server
 ```bash
 # the setting of log property
 ZOO_LOG_DIR: the directory to store the logs
-ZOO_LOG4J_PROP: the level of logs to print
 ```
 
 <a name="zkCleanup"></a>
diff --git a/zookeeper-metrics-providers/zookeeper-prometheus-metrics/src/test/resources/log4j.properties b/zookeeper-metrics-providers/zookeeper-prometheus-metrics/src/test/resources/log4j.properties
deleted file mode 100644
index d7f930d..0000000
--- a/zookeeper-metrics-providers/zookeeper-prometheus-metrics/src/test/resources/log4j.properties
+++ /dev/null
@@ -1,65 +0,0 @@
-# Copyright 2012 The Apache Software Foundation
-#
-# Licensed to the Apache Software Foundation (ASF) under one
-# or more contributor license agreements.  See the NOTICE file
-# distributed with this work for additional information
-# regarding copyright ownership.  The ASF licenses this file
-# to you under the Apache License, Version 2.0 (the
-# "License"); you may not use this file except in compliance
-# with the License.  You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-# Define some default values that can be overridden by system properties
-zookeeper.root.logger=INFO, CONSOLE
-
-zookeeper.console.threshold=INFO
-
-zookeeper.log.dir=.
-zookeeper.log.file=zookeeper.log
-zookeeper.log.threshold=INFO
-zookeeper.log.maxfilesize=256MB
-zookeeper.log.maxbackupindex=20
-
-zookeeper.tracelog.dir=${zookeeper.log.dir}
-zookeeper.tracelog.file=zookeeper_trace.log
-
-log4j.rootLogger=${zookeeper.root.logger}
-
-#
-# console
-# Add "console" to rootlogger above if you want to use this
-#
-log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
-log4j.appender.CONSOLE.Threshold=${zookeeper.console.threshold}
-log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
-log4j.appender.CONSOLE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n
-
-#
-# Add ROLLINGFILE to rootLogger to get log file output
-#
-log4j.appender.ROLLINGFILE=org.apache.log4j.RollingFileAppender
-log4j.appender.ROLLINGFILE.Threshold=${zookeeper.log.threshold}
-log4j.appender.ROLLINGFILE.File=${zookeeper.log.dir}/${zookeeper.log.file}
-log4j.appender.ROLLINGFILE.MaxFileSize=${zookeeper.log.maxfilesize}
-log4j.appender.ROLLINGFILE.MaxBackupIndex=${zookeeper.log.maxbackupindex}
-log4j.appender.ROLLINGFILE.layout=org.apache.log4j.PatternLayout
-log4j.appender.ROLLINGFILE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n
-
-#
-# Add TRACEFILE to rootLogger to get log file output
-#    Log TRACE level and above messages to a log file
-#
-log4j.appender.TRACEFILE=org.apache.log4j.FileAppender
-log4j.appender.TRACEFILE.Threshold=TRACE
-log4j.appender.TRACEFILE.File=${zookeeper.tracelog.dir}/${zookeeper.tracelog.file}
-
-log4j.appender.TRACEFILE.layout=org.apache.log4j.PatternLayout
-### Notice we are including log4j's NDC here (%x)
-log4j.appender.TRACEFILE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L][%x] - %m%n
diff --git a/zookeeper-metrics-providers/zookeeper-prometheus-metrics/src/test/resources/logback.xml b/zookeeper-metrics-providers/zookeeper-prometheus-metrics/src/test/resources/logback.xml
new file mode 100644
index 0000000..a1e6277
--- /dev/null
+++ b/zookeeper-metrics-providers/zookeeper-prometheus-metrics/src/test/resources/logback.xml
@@ -0,0 +1,36 @@
+<!--
+ Copyright 2022 The Apache Software Foundation
+
+ Licensed to the Apache Software Foundation (ASF) under one
+ or more contributor license agreements.  See the NOTICE file
+ distributed with this work for additional information
+ regarding copyright ownership.  The ASF licenses this file
+ to you under the Apache License, Version 2.0 (the
+ "License"); you may not use this file except in compliance
+ with the License.  You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+
+ Define some default values that can be overridden by system properties
+-->
+<configuration>
+
+  <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
+    <encoder>
+      <pattern>%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n</pattern>
+    </encoder>
+    <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
+      <level>INFO</level>
+    </filter>
+  </appender>
+
+  <root level="INFO">
+    <appender-ref ref="CONSOLE" />
+  </root>
+</configuration>
diff --git a/zookeeper-server/pom.xml b/zookeeper-server/pom.xml
index 4fd4f98..14c74ca 100755
--- a/zookeeper-server/pom.xml
+++ b/zookeeper-server/pom.xml
@@ -75,8 +75,12 @@
       <artifactId>slf4j-api</artifactId>
     </dependency>
     <dependency>
-      <groupId>org.slf4j</groupId>
-      <artifactId>slf4j-log4j12</artifactId>
+      <groupId>ch.qos.logback</groupId>
+      <artifactId>logback-core</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>ch.qos.logback</groupId>
+      <artifactId>logback-classic</artifactId>
     </dependency>
     <dependency>
       <groupId>org.eclipse.jetty</groupId>
@@ -119,10 +123,6 @@
        <scope>provided</scope>
     </dependency>
     <dependency>
-      <groupId>log4j</groupId>
-      <artifactId>log4j</artifactId>
-    </dependency>
-    <dependency>
       <groupId>org.apache.kerby</groupId>
       <artifactId>kerb-core</artifactId>
       <scope>test</scope>
diff --git a/zookeeper-server/src/main/java/org/apache/zookeeper/audit/Log4jAuditLogger.java b/zookeeper-server/src/main/java/org/apache/zookeeper/audit/Slf4jAuditLogger.java
similarity index 87%
rename from zookeeper-server/src/main/java/org/apache/zookeeper/audit/Log4jAuditLogger.java
rename to zookeeper-server/src/main/java/org/apache/zookeeper/audit/Slf4jAuditLogger.java
index c4efc1c..b162e74 100644
--- a/zookeeper-server/src/main/java/org/apache/zookeeper/audit/Log4jAuditLogger.java
+++ b/zookeeper-server/src/main/java/org/apache/zookeeper/audit/Slf4jAuditLogger.java
@@ -22,10 +22,10 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 /**
- * Log4j based audit logger
+ * Slf4j based audit logger
  */
-public class Log4jAuditLogger implements AuditLogger {
-    private static final Logger LOG = LoggerFactory.getLogger(Log4jAuditLogger.class);
+public class Slf4jAuditLogger implements AuditLogger {
+    private static final Logger LOG = LoggerFactory.getLogger(Slf4jAuditLogger.class);
 
     @Override
     public void logAuditEvent(AuditEvent auditEvent) {
diff --git a/zookeeper-server/src/main/java/org/apache/zookeeper/audit/ZKAuditProvider.java b/zookeeper-server/src/main/java/org/apache/zookeeper/audit/ZKAuditProvider.java
index 00646ba..864d236 100644
--- a/zookeeper-server/src/main/java/org/apache/zookeeper/audit/ZKAuditProvider.java
+++ b/zookeeper-server/src/main/java/org/apache/zookeeper/audit/ZKAuditProvider.java
@@ -46,7 +46,7 @@ public class ZKAuditProvider {
     private static AuditLogger getAuditLogger() {
         String auditLoggerClass = System.getProperty(AUDIT_IMPL_CLASS);
         if (auditLoggerClass == null) {
-            auditLoggerClass = Log4jAuditLogger.class.getName();
+            auditLoggerClass = Slf4jAuditLogger.class.getName();
         }
         try {
             Constructor<?> clientCxnConstructor = Class.forName(auditLoggerClass)
diff --git a/zookeeper-server/src/main/java/org/apache/zookeeper/server/ZooTrace.java b/zookeeper-server/src/main/java/org/apache/zookeeper/server/ZooTrace.java
index e9d1eb1..464d818 100644
--- a/zookeeper-server/src/main/java/org/apache/zookeeper/server/ZooTrace.java
+++ b/zookeeper-server/src/main/java/org/apache/zookeeper/server/ZooTrace.java
@@ -27,7 +27,7 @@ import org.slf4j.LoggerFactory;
  * This class encapsulates and centralizes tracing for the ZooKeeper server.
  * Trace messages go to the log with TRACE level.
  * <p>
- * Log4j must be correctly configured to capture the TRACE messages.
+ * Logback must be correctly configured to capture the TRACE messages.
  */
 public class ZooTrace {
 
diff --git a/zookeeper-server/src/main/resources/NOTICE.txt b/zookeeper-server/src/main/resources/NOTICE.txt
index 1b0fb95..efdd6b4 100644
--- a/zookeeper-server/src/main/resources/NOTICE.txt
+++ b/zookeeper-server/src/main/resources/NOTICE.txt
@@ -81,13 +81,13 @@ framework, which can be obtained at:
   * HOMEPAGE:
     * http://commons.apache.org/logging/
 
-This product optionally depends on 'Apache Log4J', a logging framework,
+This product optionally depends on 'Apache Logback', a logging framework,
 which can be obtained at:
 
   * LICENSE:
-    * license/LICENSE.log4j.txt (Apache License 2.0)
+    * license/LICENSE.logback.txt (Eclipse Public License 1.0)
   * HOMEPAGE:
-    * http://logging.apache.org/log4j/
+    * https://logback.qos.ch/
 
 This product optionally depends on 'JBoss Logging', a logging framework,
 which can be obtained at:
diff --git a/zookeeper-server/src/main/resources/lib/log4j-1.2.17.LICENSE.txt b/zookeeper-server/src/main/resources/lib/log4j-1.2.17.LICENSE.txt
deleted file mode 100644
index 6279e52..0000000
--- a/zookeeper-server/src/main/resources/lib/log4j-1.2.17.LICENSE.txt
+++ /dev/null
@@ -1,202 +0,0 @@
-
-                                 Apache License
-                           Version 2.0, January 2004
-                        http://www.apache.org/licenses/
-
-   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
-
-   1. Definitions.
-
-      "License" shall mean the terms and conditions for use, reproduction,
-      and distribution as defined by Sections 1 through 9 of this document.
-
-      "Licensor" shall mean the copyright owner or entity authorized by
-      the copyright owner that is granting the License.
-
-      "Legal Entity" shall mean the union of the acting entity and all
-      other entities that control, are controlled by, or are under common
-      control with that entity. For the purposes of this definition,
-      "control" means (i) the power, direct or indirect, to cause the
-      direction or management of such entity, whether by contract or
-      otherwise, or (ii) ownership of fifty percent (50%) or more of the
-      outstanding shares, or (iii) beneficial ownership of such entity.
-
-      "You" (or "Your") shall mean an individual or Legal Entity
-      exercising permissions granted by this License.
-
-      "Source" form shall mean the preferred form for making modifications,
-      including but not limited to software source code, documentation
-      source, and configuration files.
-
-      "Object" form shall mean any form resulting from mechanical
-      transformation or translation of a Source form, including but
-      not limited to compiled object code, generated documentation,
-      and conversions to other media types.
-
-      "Work" shall mean the work of authorship, whether in Source or
-      Object form, made available under the License, as indicated by a
-      copyright notice that is included in or attached to the work
-      (an example is provided in the Appendix below).
-
-      "Derivative Works" shall mean any work, whether in Source or Object
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diff --git a/zookeeper-server/src/main/resources/lib/logback-classic-1.2.10.LICENSE.txt b/zookeeper-server/src/main/resources/lib/logback-classic-1.2.10.LICENSE.txt
new file mode 100644
index 0000000..46f4f25
--- /dev/null
+++ b/zookeeper-server/src/main/resources/lib/logback-classic-1.2.10.LICENSE.txt
@@ -0,0 +1,414 @@
+This program and the accompanying materials are made available under the
+terms of the Eclipse Public License 2.0 which is available at
+http://www.eclipse.org/legal/epl-2.0, or the Apache Software License
+2.0 which is available at https://www.apache.org/licenses/LICENSE-2.0.
+
+
+
+Eclipse Public License - v 1.0
+
+THE ACCOMPANYING PROGRAM IS PROVIDED UNDER THE TERMS OF THIS ECLIPSE PUBLIC
+LICENSE ("AGREEMENT"). ANY USE, REPRODUCTION OR DISTRIBUTION OF THE PROGRAM
+CONSTITUTES RECIPIENT'S ACCEPTANCE OF THIS AGREEMENT.
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+1. DEFINITIONS
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+"Contribution" means:
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+      comment syntax for the file format. We also recommend that a
+      file or class name and description of purpose be included on the
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+
+   Copyright [yyyy] [name of copyright owner]
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
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+       http://www.apache.org/licenses/LICENSE-2.0
+
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diff --git a/zookeeper-server/src/main/resources/lib/logback-core-1.2.10.LICENSE.txt b/zookeeper-server/src/main/resources/lib/logback-core-1.2.10.LICENSE.txt
new file mode 100644
index 0000000..46f4f25
--- /dev/null
+++ b/zookeeper-server/src/main/resources/lib/logback-core-1.2.10.LICENSE.txt
@@ -0,0 +1,414 @@
+This program and the accompanying materials are made available under the
+terms of the Eclipse Public License 2.0 which is available at
+http://www.eclipse.org/legal/epl-2.0, or the Apache Software License
+2.0 which is available at https://www.apache.org/licenses/LICENSE-2.0.
+
+
+
+Eclipse Public License - v 1.0
+
+THE ACCOMPANYING PROGRAM IS PROVIDED UNDER THE TERMS OF THIS ECLIPSE PUBLIC
+LICENSE ("AGREEMENT"). ANY USE, REPRODUCTION OR DISTRIBUTION OF THE PROGRAM
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diff --git a/zookeeper-server/src/test/java/org/apache/zookeeper/audit/Log4jAuditLoggerTest.java b/zookeeper-server/src/test/java/org/apache/zookeeper/audit/Slf4JAuditLoggerTest.java
similarity index 94%
rename from zookeeper-server/src/test/java/org/apache/zookeeper/audit/Log4jAuditLoggerTest.java
rename to zookeeper-server/src/test/java/org/apache/zookeeper/audit/Slf4JAuditLoggerTest.java
index 0080b01..df3b831 100644
--- a/zookeeper-server/src/test/java/org/apache/zookeeper/audit/Log4jAuditLoggerTest.java
+++ b/zookeeper-server/src/test/java/org/apache/zookeeper/audit/Slf4JAuditLoggerTest.java
@@ -19,6 +19,7 @@ package org.apache.zookeeper.audit;
 
 import static org.apache.zookeeper.test.ClientBase.CONNECTION_TIMEOUT;
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.LineNumberReader;
@@ -27,11 +28,6 @@ import java.net.InetAddress;
 import java.net.InetSocketAddress;
 import java.util.ArrayList;
 import java.util.List;
-import org.apache.log4j.Layout;
-import org.apache.log4j.Level;
-import org.apache.log4j.Logger;
-import org.apache.log4j.SimpleLayout;
-import org.apache.log4j.WriterAppender;
 import org.apache.zookeeper.CreateMode;
 import org.apache.zookeeper.KeeperException;
 import org.apache.zookeeper.KeeperException.Code;
@@ -48,33 +44,28 @@ import org.apache.zookeeper.server.ServerCnxn;
 import org.apache.zookeeper.server.quorum.QuorumPeerTestBase;
 import org.apache.zookeeper.test.ClientBase;
 import org.apache.zookeeper.test.ClientBase.CountdownWatcher;
+import org.apache.zookeeper.test.LoggerTestTool;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
-
-public class Log4jAuditLoggerTest extends QuorumPeerTestBase {
-    private static final Logger LOG = Logger.getLogger(Log4jAuditLoggerTest.class);
+public class Slf4JAuditLoggerTest extends QuorumPeerTestBase {
+    private static final Logger LOG = LoggerFactory.getLogger(Slf4JAuditLoggerTest.class);
     private static int SERVER_COUNT = 3;
     private static MainThread[] mt;
     private static ZooKeeper zk;
-    private static Logger zlogger;
-    private static WriterAppender appender;
     private static ByteArrayOutputStream os;
 
     @BeforeAll
     public static void setUpBeforeClass() throws Exception {
         System.setProperty(ZKAuditProvider.AUDIT_ENABLE, "true");
         // setup the logger to capture all logs
-        Layout layout = new SimpleLayout();
-        os = new ByteArrayOutputStream();
-        appender = new WriterAppender(layout, os);
-        appender.setImmediateFlush(true);
-        appender.setThreshold(Level.INFO);
-        zlogger = Logger.getLogger(Log4jAuditLogger.class);
-        zlogger.addAppender(appender);
+        LoggerTestTool loggerTestTool = new LoggerTestTool(Slf4jAuditLogger.class);
+        os = loggerTestTool.getOutputStream();
         mt = startQuorum();
         zk = ClientBase.createZKClient("127.0.0.1:" + mt[0].getQuorumPeer().getClientPort());
         //Verify start audit log here itself
@@ -322,8 +313,7 @@ public class Log4jAuditLoggerTest extends QuorumPeerTestBase {
         String searchString = " - ";
         int logStartIndex = log.indexOf(searchString);
         String auditLog = log.substring(logStartIndex + searchString.length());
-        assertEquals(expectedLog, auditLog);
-
+        assertTrue(auditLog.endsWith(expectedLog));
     }
 
     private static void verifyLogs(String expectedLog, List<String> logs) {
@@ -428,12 +418,5 @@ public class Log4jAuditLoggerTest extends QuorumPeerTestBase {
                 e.printStackTrace();
             }
         }
-        try {
-            zlogger.removeAppender(appender);
-            os.close();
-        } catch (IOException e) {
-            e.printStackTrace();
-        }
     }
-
 }
diff --git a/zookeeper-server/src/test/java/org/apache/zookeeper/audit/StandaloneServerAuditTest.java b/zookeeper-server/src/test/java/org/apache/zookeeper/audit/StandaloneServerAuditTest.java
index 0815b9f..8cadf3e 100644
--- a/zookeeper-server/src/test/java/org/apache/zookeeper/audit/StandaloneServerAuditTest.java
+++ b/zookeeper-server/src/test/java/org/apache/zookeeper/audit/StandaloneServerAuditTest.java
@@ -18,7 +18,6 @@
 
 package org.apache.zookeeper.audit;
 
-
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import java.io.ByteArrayOutputStream;
@@ -27,36 +26,24 @@ import java.io.LineNumberReader;
 import java.io.StringReader;
 import java.util.ArrayList;
 import java.util.List;
-import org.apache.log4j.Layout;
-import org.apache.log4j.Level;
-import org.apache.log4j.Logger;
-import org.apache.log4j.SimpleLayout;
-import org.apache.log4j.WriterAppender;
 import org.apache.zookeeper.CreateMode;
 import org.apache.zookeeper.KeeperException;
 import org.apache.zookeeper.ZooDefs;
 import org.apache.zookeeper.ZooKeeper;
 import org.apache.zookeeper.test.ClientBase;
+import org.apache.zookeeper.test.LoggerTestTool;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
 
-
-
 public class StandaloneServerAuditTest extends ClientBase {
     private static ByteArrayOutputStream os;
 
     @BeforeAll
     public static void setup() {
         System.setProperty(ZKAuditProvider.AUDIT_ENABLE, "true");
-        // setup the logger to capture all the logs
-        Layout layout = new SimpleLayout();
-        os = new ByteArrayOutputStream();
-        WriterAppender appender = new WriterAppender(layout, os);
-        appender.setImmediateFlush(true);
-        appender.setThreshold(Level.INFO);
-        Logger zLogger = Logger.getLogger(Log4jAuditLogger.class);
-        zLogger.addAppender(appender);
+        LoggerTestTool loggerTestTool = new LoggerTestTool(Slf4jAuditLogger.class);
+        os = loggerTestTool.getOutputStream();
     }
 
     @AfterAll
diff --git a/zookeeper-server/src/test/java/org/apache/zookeeper/server/quorum/QuorumPeerMainTest.java b/zookeeper-server/src/test/java/org/apache/zookeeper/server/quorum/QuorumPeerMainTest.java
index 724356e..be81aa6 100644
--- a/zookeeper-server/src/test/java/org/apache/zookeeper/server/quorum/QuorumPeerMainTest.java
+++ b/zookeeper-server/src/test/java/org/apache/zookeeper/server/quorum/QuorumPeerMainTest.java
@@ -47,10 +47,6 @@ import java.util.concurrent.TimeoutException;
 import java.util.regex.Pattern;
 import javax.security.sasl.SaslException;
 import org.apache.commons.io.FileUtils;
-import org.apache.log4j.Level;
-import org.apache.log4j.Logger;
-import org.apache.log4j.PatternLayout;
-import org.apache.log4j.WriterAppender;
 import org.apache.zookeeper.CreateMode;
 import org.apache.zookeeper.KeeperException;
 import org.apache.zookeeper.PortAssignment;
@@ -66,6 +62,7 @@ import org.apache.zookeeper.server.ServerMetrics;
 import org.apache.zookeeper.server.persistence.FileTxnSnapLog;
 import org.apache.zookeeper.server.quorum.Leader.Proposal;
 import org.apache.zookeeper.test.ClientBase;
+import org.apache.zookeeper.test.LoggerTestTool;
 import org.junit.jupiter.api.Test;
 
 /**
@@ -339,13 +336,7 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
      * @throws InterruptedException
      */
     @Test
-    public void testElectionFraud() throws IOException, InterruptedException {
-        // capture QuorumPeer logging
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.INFO);
-        Logger qlogger = Logger.getLogger(QuorumPeer.class);
-        qlogger.addAppender(appender);
-
+    public void testElectionFraud() throws Exception {
         numServers = 3;
 
         // used for assertions later
@@ -353,7 +344,9 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
         boolean foundLooking = false;
         boolean foundFollowing = false;
 
-        try {
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool(QuorumPeer.class)) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
+
             // spin up a quorum, we use a small ticktime to make the test run faster
             servers = LaunchServers(numServers, 500);
 
@@ -411,8 +404,6 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
                     break;
                 }
             }
-        } finally {
-            qlogger.removeAppender(appender);
         }
 
         assertTrue(foundLeading, "falseLeader never attempts to become leader");
@@ -427,13 +418,9 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
     public void testBadPeerAddressInQuorum() throws Exception {
         ClientBase.setupTestEnv();
 
-        // setup the logger to capture all logs
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.WARN);
-        Logger qlogger = Logger.getLogger("org.apache.zookeeper.server.quorum");
-        qlogger.addAppender(appender);
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool("org.apache.zookeeper.server.quorum")) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
 
-        try {
             final int CLIENT_PORT_QP1 = PortAssignment.unique();
             final int CLIENT_PORT_QP2 = PortAssignment.unique();
 
@@ -452,21 +439,18 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
             assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP1, ClientBase.CONNECTION_TIMEOUT),
                     "waiting for server 1 down");
 
-        } finally {
-            qlogger.removeAppender(appender);
-        }
-
-        LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
-        String line;
-        boolean found = false;
-        Pattern p = Pattern.compile(".*Cannot open channel to .* at election address .*");
-        while ((line = r.readLine()) != null) {
-            found = p.matcher(line).matches();
-            if (found) {
-                break;
+            LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
+            String line;
+            boolean found = false;
+            Pattern p = Pattern.compile(".*Cannot open channel to .* at election address .*");
+            while ((line = r.readLine()) != null) {
+                found = p.matcher(line).matches();
+                if (found) {
+                    break;
+                }
             }
+            assertTrue(found, "complains about host");
         }
-        assertTrue(found, "complains about host");
     }
 
     /**
@@ -476,15 +460,11 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
     public void testInconsistentPeerType() throws Exception {
         ClientBase.setupTestEnv();
 
-        // setup the logger to capture all logs
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.INFO);
-        Logger qlogger = Logger.getLogger("org.apache.zookeeper.server.quorum");
-        qlogger.addAppender(appender);
-
         // test the most likely situation only: server is stated as observer in
         // servers list, but there's no "peerType=observer" token in config
-        try {
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool("org.apache.zookeeper.server.quorum")) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
+
             final int CLIENT_PORT_QP1 = PortAssignment.unique();
             final int CLIENT_PORT_QP2 = PortAssignment.unique();
             final int CLIENT_PORT_QP3 = PortAssignment.unique();
@@ -518,28 +498,25 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
             assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP3, ClientBase.CONNECTION_TIMEOUT),
                     "waiting for server 3 down");
 
-        } finally {
-            qlogger.removeAppender(appender);
-        }
-
-        LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
-        String line;
-        boolean warningPresent = false;
-        boolean defaultedToObserver = false;
-        Pattern pWarn = Pattern.compile(".*Peer type from servers list.* doesn't match peerType.*");
-        Pattern pObserve = Pattern.compile(".*OBSERVING.*");
-        while ((line = r.readLine()) != null) {
-            if (pWarn.matcher(line).matches()) {
-                warningPresent = true;
-            }
-            if (pObserve.matcher(line).matches()) {
-                defaultedToObserver = true;
-            }
-            if (warningPresent && defaultedToObserver) {
-                break;
+            LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
+            String line;
+            boolean warningPresent = false;
+            boolean defaultedToObserver = false;
+            Pattern pWarn = Pattern.compile(".*Peer type from servers list.* doesn't match peerType.*");
+            Pattern pObserve = Pattern.compile(".*OBSERVING.*");
+            while ((line = r.readLine()) != null) {
+                if (pWarn.matcher(line).matches()) {
+                    warningPresent = true;
+                }
+                if (pObserve.matcher(line).matches()) {
+                    defaultedToObserver = true;
+                }
+                if (warningPresent && defaultedToObserver) {
+                    break;
+                }
             }
+            assertTrue(warningPresent && defaultedToObserver, "Should warn about inconsistent peer type");
         }
-        assertTrue(warningPresent && defaultedToObserver, "Should warn about inconsistent peer type");
     }
 
     /**
@@ -597,14 +574,9 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
     public void testQuorumDefaults() throws Exception {
         ClientBase.setupTestEnv();
 
-        // setup the logger to capture all logs
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.INFO);
-        appender.setImmediateFlush(true);
-        Logger zlogger = Logger.getLogger("org.apache.zookeeper");
-        zlogger.addAppender(appender);
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool("org.apache.zookeeper")) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
 
-        try {
             final int CLIENT_PORT_QP1 = PortAssignment.unique();
             final int CLIENT_PORT_QP2 = PortAssignment.unique();
 
@@ -629,21 +601,19 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
             assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP2, ClientBase.CONNECTION_TIMEOUT),
                     "waiting for server 2 down");
 
-        } finally {
-            zlogger.removeAppender(appender);
-        }
-        os.close();
-        LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
-        String line;
-        boolean found = false;
-        Pattern p = Pattern.compile(".*FastLeaderElection.*");
-        while ((line = r.readLine()) != null) {
-            found = p.matcher(line).matches();
-            if (found) {
-                break;
+            os.close();
+            LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
+            String line;
+            boolean found = false;
+            Pattern p = Pattern.compile(".*FastLeaderElection.*");
+            while ((line = r.readLine()) != null) {
+                found = p.matcher(line).matches();
+                if (found) {
+                    break;
+                }
             }
+            assertTrue(found, "fastleaderelection used");
         }
-        assertTrue(found, "fastleaderelection used");
     }
 
     /**
@@ -858,13 +828,8 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
         boolean foundLeading = false;
         boolean foundFollowing = false;
 
-        // capture QuorumPeer logging
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.DEBUG);
-        Logger qlogger = Logger.getLogger("org.apache.zookeeper.server.quorum");
-        qlogger.addAppender(appender);
-
-        try {
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool(QuorumPeerMainTest.class)) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
             Servers svrs = new Servers();
             svrs.clientPorts = new int[numServers];
             for (int i = 0; i < numServers; i++) {
@@ -944,8 +909,6 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
                     "Corrupt peer should not attempt connection to out of view leader");
             }
 
-        } finally {
-            qlogger.removeAppender(appender);
         }
     }
 
@@ -995,13 +958,6 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
 
     }
 
-    private WriterAppender getConsoleAppender(ByteArrayOutputStream os, Level level) {
-        String loggingPattern = ((PatternLayout) Logger.getRootLogger().getAppender("CONSOLE").getLayout()).getConversionPattern();
-        WriterAppender appender = new WriterAppender(new PatternLayout(loggingPattern), os);
-        appender.setThreshold(level);
-        return appender;
-    }
-
     private String getUniquePortCfgForId(int id) {
         return String.format("server.%d=127.0.0.1:%d:%d", id, PortAssignment.unique(), PortAssignment.unique());
     }
@@ -1291,44 +1247,34 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
         ClientBase.setupTestEnv();
         BaseTestMetricsProvider.MetricsProviderCapturingLifecycle.reset();
 
-        // setup the logger to capture all logs
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.WARN);
-        Logger qlogger = Logger.getLogger("org.apache.zookeeper.server.quorum");
-        qlogger.addAppender(appender);
-
-        try {
-            final int CLIENT_PORT_QP1 = PortAssignment.unique();
-            final int CLIENT_PORT_QP2 = PortAssignment.unique();
+        final int CLIENT_PORT_QP1 = PortAssignment.unique();
+        final int CLIENT_PORT_QP2 = PortAssignment.unique();
 
-            String quorumCfgSectionServer = "server.1=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP1
-                                            + "\nserver.2=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP2 + "\n";
+        String quorumCfgSectionServer = "server.1=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP1
+                                        + "\nserver.2=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP2 + "\n";
 
-            // server 1 boots with a MetricsProvider
-            String quorumCfgSectionServer1 = quorumCfgSectionServer
-                                             + "metricsProvider.className=" + BaseTestMetricsProvider.MetricsProviderCapturingLifecycle.class.getName() + "\n";
+        // server 1 boots with a MetricsProvider
+        String quorumCfgSectionServer1 = quorumCfgSectionServer
+                                         + "metricsProvider.className=" + BaseTestMetricsProvider.MetricsProviderCapturingLifecycle.class.getName() + "\n";
 
-            MainThread q1 = new MainThread(1, CLIENT_PORT_QP1, quorumCfgSectionServer1);
-            MainThread q2 = new MainThread(2, CLIENT_PORT_QP2, quorumCfgSectionServer);
-            q1.start();
-            q2.start();
+        MainThread q1 = new MainThread(1, CLIENT_PORT_QP1, quorumCfgSectionServer1);
+        MainThread q2 = new MainThread(2, CLIENT_PORT_QP2, quorumCfgSectionServer);
+        q1.start();
+        q2.start();
 
-            boolean isup1 = ClientBase.waitForServerUp("127.0.0.1:" + CLIENT_PORT_QP1, 30000);
-            boolean isup2 = ClientBase.waitForServerUp("127.0.0.1:" + CLIENT_PORT_QP2, 30000);
-            assertTrue(isup1, "Server 1 never came up");
-            assertTrue(isup2, "Server 2 never came up");
+        boolean isup1 = ClientBase.waitForServerUp("127.0.0.1:" + CLIENT_PORT_QP1, 30000);
+        boolean isup2 = ClientBase.waitForServerUp("127.0.0.1:" + CLIENT_PORT_QP2, 30000);
+        assertTrue(isup1, "Server 1 never came up");
+        assertTrue(isup2, "Server 2 never came up");
 
-            q1.shutdown();
-            q2.shutdown();
+        q1.shutdown();
+        q2.shutdown();
 
-            assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP1, ClientBase.CONNECTION_TIMEOUT),
-                    "waiting for server 1 down");
+        assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP1, ClientBase.CONNECTION_TIMEOUT),
+                "waiting for server 1 down");
 
-            assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP2, ClientBase.CONNECTION_TIMEOUT),
-                    "waiting for server 2 down");
-        } finally {
-            qlogger.removeAppender(appender);
-        }
+        assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP2, ClientBase.CONNECTION_TIMEOUT),
+                "waiting for server 2 down");
 
         assertTrue(BaseTestMetricsProvider.MetricsProviderCapturingLifecycle.configureCalled.get(), "metrics provider lifecycle error");
         assertTrue(BaseTestMetricsProvider.MetricsProviderCapturingLifecycle.startCalled.get(), "metrics provider lifecycle error");
@@ -1344,46 +1290,36 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
         ClientBase.setupTestEnv();
         BaseTestMetricsProvider.MetricsProviderWithConfiguration.httpPort.set(0);
 
-        // setup the logger to capture all logs
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.WARN);
-        Logger qlogger = Logger.getLogger("org.apache.zookeeper.server.quorum");
-        qlogger.addAppender(appender);
+        final int CLIENT_PORT_QP1 = PortAssignment.unique();
+        final int CLIENT_PORT_QP2 = PortAssignment.unique();
 
-        try {
-            final int CLIENT_PORT_QP1 = PortAssignment.unique();
-            final int CLIENT_PORT_QP2 = PortAssignment.unique();
+        String quorumCfgSectionServer = "server.1=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP1 + "\n"
+                                        + "server.2=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP2 + "\n";
 
-            String quorumCfgSectionServer = "server.1=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP1 + "\n"
-                                            + "server.2=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP2 + "\n";
+        // server 1 boots with a MetricsProvider
+        String quorumCfgSectionServer1 = quorumCfgSectionServer
+                                         + "metricsProvider.className="
+                                         + BaseTestMetricsProvider.MetricsProviderWithConfiguration.class.getName()
+                                         + "\n" + "metricsProvider.httpPort=1234";
 
-            // server 1 boots with a MetricsProvider
-            String quorumCfgSectionServer1 = quorumCfgSectionServer
-                                             + "metricsProvider.className="
-                                             + BaseTestMetricsProvider.MetricsProviderWithConfiguration.class.getName()
-                                             + "\n" + "metricsProvider.httpPort=1234";
+        MainThread q1 = new MainThread(1, CLIENT_PORT_QP1, quorumCfgSectionServer1);
+        MainThread q2 = new MainThread(2, CLIENT_PORT_QP2, quorumCfgSectionServer);
+        q1.start();
+        q2.start();
 
-            MainThread q1 = new MainThread(1, CLIENT_PORT_QP1, quorumCfgSectionServer1);
-            MainThread q2 = new MainThread(2, CLIENT_PORT_QP2, quorumCfgSectionServer);
-            q1.start();
-            q2.start();
+        boolean isup1 = ClientBase.waitForServerUp("127.0.0.1:" + CLIENT_PORT_QP1, 30000);
+        boolean isup2 = ClientBase.waitForServerUp("127.0.0.1:" + CLIENT_PORT_QP2, 30000);
+        assertTrue(isup1, "Server 1 never came up");
+        assertTrue(isup2, "Server 2 never came up");
 
-            boolean isup1 = ClientBase.waitForServerUp("127.0.0.1:" + CLIENT_PORT_QP1, 30000);
-            boolean isup2 = ClientBase.waitForServerUp("127.0.0.1:" + CLIENT_PORT_QP2, 30000);
-            assertTrue(isup1, "Server 1 never came up");
-            assertTrue(isup2, "Server 2 never came up");
-
-            q1.shutdown();
-            q2.shutdown();
+        q1.shutdown();
+        q2.shutdown();
 
-            assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP1, ClientBase.CONNECTION_TIMEOUT),
-                    "waiting for server 1 down");
+        assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP1, ClientBase.CONNECTION_TIMEOUT),
+                "waiting for server 1 down");
 
-            assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP2, ClientBase.CONNECTION_TIMEOUT),
-                    "waiting for server 2 down");
-        } finally {
-            qlogger.removeAppender(appender);
-        }
+        assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP2, ClientBase.CONNECTION_TIMEOUT),
+                "waiting for server 2 down");
 
         assertEquals(1234, BaseTestMetricsProvider.MetricsProviderWithConfiguration.httpPort.get());
     }
@@ -1396,13 +1332,9 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
         ClientBase.setupTestEnv();
         BaseTestMetricsProvider.MetricsProviderCapturingLifecycle.reset();
 
-        // setup the logger to capture all logs
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.WARN);
-        Logger qlogger = Logger.getLogger("org.apache.zookeeper.server.quorum");
-        qlogger.addAppender(appender);
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool("org.apache.zookeeper.server.quorum")) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
 
-        try {
             final int CLIENT_PORT_QP1 = PortAssignment.unique();
             final int CLIENT_PORT_QP2 = PortAssignment.unique();
 
@@ -1433,23 +1365,20 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
 
             assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP2, ClientBase.CONNECTION_TIMEOUT),
                     "waiting for server 2 down");
-        } finally {
-            qlogger.removeAppender(appender);
-        }
-
-        assertTrue(BaseTestMetricsProvider.MetricsProviderWithErrorInStop.stopCalled.get(), "metrics provider lifecycle error");
+            assertTrue(BaseTestMetricsProvider.MetricsProviderWithErrorInStop.stopCalled.get(), "metrics provider lifecycle error");
 
-        LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
-        String line;
-        boolean found = false;
-        Pattern p = Pattern.compile(".*Error while stopping metrics.*");
-        while ((line = r.readLine()) != null) {
-            found = p.matcher(line).matches();
-            if (found) {
-                break;
+            LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
+            String line;
+            boolean found = false;
+            Pattern p = Pattern.compile(".*Error while stopping metrics.*");
+            while ((line = r.readLine()) != null) {
+                found = p.matcher(line).matches();
+                if (found) {
+                    break;
+                }
             }
+            assertTrue(found, "complains about metrics provider");
         }
-        assertTrue(found, "complains about metrics provider");
     }
 
     /**
@@ -1459,13 +1388,9 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
     public void testInvalidMetricsProvider() throws Exception {
         ClientBase.setupTestEnv();
 
-        // setup the logger to capture all logs
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.WARN);
-        Logger qlogger = Logger.getLogger("org.apache.zookeeper.server.quorum");
-        qlogger.addAppender(appender);
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool("org.apache.zookeeper.server.quorum")) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
 
-        try {
             final int CLIENT_PORT_QP1 = PortAssignment.unique();
 
             String quorumCfgSection = "server.1=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP1
@@ -1484,21 +1409,18 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
             assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP1, ClientBase.CONNECTION_TIMEOUT),
                     "waiting for server 1 down");
 
-        } finally {
-            qlogger.removeAppender(appender);
-        }
-
-        LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
-        String line;
-        boolean found = false;
-        Pattern p = Pattern.compile(".*BadClass.*");
-        while ((line = r.readLine()) != null) {
-            found = p.matcher(line).matches();
-            if (found) {
-                break;
+            LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
+            String line;
+            boolean found = false;
+            Pattern p = Pattern.compile(".*BadClass.*");
+            while ((line = r.readLine()) != null) {
+                found = p.matcher(line).matches();
+                if (found) {
+                    break;
+                }
             }
+            assertTrue(found, "complains about metrics provider");
         }
-        assertTrue(found, "complains about metrics provider");
     }
 
     /**
@@ -1508,13 +1430,9 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
     public void testFaultyMetricsProviderOnStart() throws Exception {
         ClientBase.setupTestEnv();
 
-        // setup the logger to capture all logs
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.WARN);
-        Logger qlogger = Logger.getLogger("org.apache.zookeeper.server.quorum");
-        qlogger.addAppender(appender);
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool("org.apache.zookeeper.server.quorum")) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
 
-        try {
             final int CLIENT_PORT_QP1 = PortAssignment.unique();
 
             String quorumCfgSection = "server.1=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP1
@@ -1534,21 +1452,18 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
             assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP1, ClientBase.CONNECTION_TIMEOUT),
                     "waiting for server 1 down");
 
-        } finally {
-            qlogger.removeAppender(appender);
-        }
-
-        LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
-        String line;
-        boolean found = false;
-        Pattern p = Pattern.compile(".*MetricsProviderLifeCycleException.*");
-        while ((line = r.readLine()) != null) {
-            found = p.matcher(line).matches();
-            if (found) {
-                break;
+            LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
+            String line;
+            boolean found = false;
+            Pattern p = Pattern.compile(".*MetricsProviderLifeCycleException.*");
+            while ((line = r.readLine()) != null) {
+                found = p.matcher(line).matches();
+                if (found) {
+                    break;
+                }
             }
+            assertTrue(found, "complains about metrics provider MetricsProviderLifeCycleException");
         }
-        assertTrue(found, "complains about metrics provider MetricsProviderLifeCycleException");
     }
 
     /**
@@ -1558,13 +1473,9 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
     public void testFaultyMetricsProviderOnConfigure() throws Exception {
         ClientBase.setupTestEnv();
 
-        // setup the logger to capture all logs
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.WARN);
-        Logger qlogger = Logger.getLogger("org.apache.zookeeper.server.quorum");
-        qlogger.addAppender(appender);
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool("org.apache.zookeeper.server.quorum")) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
 
-        try {
             final int CLIENT_PORT_QP1 = PortAssignment.unique();
 
             String quorumCfgSection = "server.1=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP1
@@ -1584,21 +1495,18 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
             assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP1, ClientBase.CONNECTION_TIMEOUT),
                     "waiting for server 1 down");
 
-        } finally {
-            qlogger.removeAppender(appender);
-        }
-
-        LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
-        String line;
-        boolean found = false;
-        Pattern p = Pattern.compile(".*MetricsProviderLifeCycleException.*");
-        while ((line = r.readLine()) != null) {
-            found = p.matcher(line).matches();
-            if (found) {
-                break;
+            LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
+            String line;
+            boolean found = false;
+            Pattern p = Pattern.compile(".*MetricsProviderLifeCycleException.*");
+            while ((line = r.readLine()) != null) {
+                found = p.matcher(line).matches();
+                if (found) {
+                    break;
+                }
             }
+            assertTrue(found, "complains about metrics provider MetricsProviderLifeCycleException");
         }
-        assertTrue(found, "complains about metrics provider MetricsProviderLifeCycleException");
     }
 
     /**
diff --git a/zookeeper-server/src/test/java/org/apache/zookeeper/test/LoggerTestTool.java b/zookeeper-server/src/test/java/org/apache/zookeeper/test/LoggerTestTool.java
new file mode 100644
index 0000000..c95a0d3
--- /dev/null
+++ b/zookeeper-server/src/test/java/org/apache/zookeeper/test/LoggerTestTool.java
@@ -0,0 +1,88 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.zookeeper.test;
+
+import ch.qos.logback.classic.Level;
+import ch.qos.logback.classic.Logger;
+import ch.qos.logback.classic.LoggerContext;
+import ch.qos.logback.classic.spi.ILoggingEvent;
+import ch.qos.logback.core.Appender;
+import ch.qos.logback.core.Layout;
+import ch.qos.logback.core.OutputStreamAppender;
+import ch.qos.logback.core.encoder.LayoutWrappingEncoder;
+import java.io.ByteArrayOutputStream;
+import org.slf4j.LoggerFactory;
+
+public class LoggerTestTool implements AutoCloseable {
+  private final ByteArrayOutputStream os;
+  private Appender<ILoggingEvent> appender;
+  private Logger qlogger;
+
+  public LoggerTestTool(Class<?> cls) {
+    os = createLoggingStream(cls);
+  }
+
+  public LoggerTestTool(String cls) {
+    os = createLoggingStream(cls);
+  }
+
+  public ByteArrayOutputStream getOutputStream() {
+    return os;
+  }
+
+  private ByteArrayOutputStream createLoggingStream(Class<?> cls) {
+    ByteArrayOutputStream os = new ByteArrayOutputStream();
+    appender = getConsoleAppender(os);
+    qlogger = (ch.qos.logback.classic.Logger) LoggerFactory.getLogger(cls);
+    qlogger.addAppender(appender);
+    qlogger.setLevel(Level.INFO);
+    appender.start();
+    return os;
+  }
+
+  private ByteArrayOutputStream createLoggingStream(String cls) {
+    ByteArrayOutputStream os = new ByteArrayOutputStream();
+    appender = getConsoleAppender(os);
+    qlogger = (ch.qos.logback.classic.Logger) LoggerFactory.getLogger(cls);
+    qlogger.addAppender(appender);
+    qlogger.setLevel(Level.INFO);
+    appender.start();
+    return os;
+  }
+
+  private OutputStreamAppender<ILoggingEvent> getConsoleAppender(ByteArrayOutputStream os) {
+    Logger rootLogger =
+        (ch.qos.logback.classic.Logger) LoggerFactory.getLogger(org.slf4j.Logger.ROOT_LOGGER_NAME);
+    Layout<ILoggingEvent> layout = ((LayoutWrappingEncoder<ILoggingEvent>)
+        ((OutputStreamAppender<ILoggingEvent>) rootLogger.getAppender("CONSOLE")).getEncoder()).getLayout();
+
+    OutputStreamAppender<ILoggingEvent> appender = new OutputStreamAppender<>();
+    appender.setContext((LoggerContext) LoggerFactory.getILoggerFactory());
+    appender.setOutputStream(os);
+    appender.setLayout(layout);
+
+    return appender;
+  }
+
+  @Override
+  public void close() throws Exception {
+    qlogger.detachAppender(appender);
+    os.close();
+  }
+}
diff --git a/zookeeper-server/src/test/java/org/apache/zookeeper/test/ReadOnlyModeTest.java b/zookeeper-server/src/test/java/org/apache/zookeeper/test/ReadOnlyModeTest.java
index 43bfb2d..c8f4ac4 100644
--- a/zookeeper-server/src/test/java/org/apache/zookeeper/test/ReadOnlyModeTest.java
+++ b/zookeeper-server/src/test/java/org/apache/zookeeper/test/ReadOnlyModeTest.java
@@ -29,10 +29,6 @@ import java.io.LineNumberReader;
 import java.io.StringReader;
 import java.util.concurrent.TimeoutException;
 import java.util.regex.Pattern;
-import org.apache.log4j.Layout;
-import org.apache.log4j.Level;
-import org.apache.log4j.Logger;
-import org.apache.log4j.WriterAppender;
 import org.apache.zookeeper.CreateMode;
 import org.apache.zookeeper.KeeperException;
 import org.apache.zookeeper.KeeperException.NotReadOnlyException;
@@ -41,6 +37,7 @@ import org.apache.zookeeper.ZKTestCase;
 import org.apache.zookeeper.ZooDefs;
 import org.apache.zookeeper.ZooKeeper;
 import org.apache.zookeeper.ZooKeeper.States;
+import org.apache.zookeeper.common.StringUtils;
 import org.apache.zookeeper.common.Time;
 import org.apache.zookeeper.test.ClientBase.CountdownWatcher;
 import org.junit.jupiter.api.AfterEach;
@@ -294,16 +291,9 @@ public class ReadOnlyModeTest extends ZKTestCase {
         qu.enableLocalSession(true);
         qu.startQuorum();
 
-        // setup the logger to capture all logs
-        Layout layout = Logger.getRootLogger().getAppender("CONSOLE").getLayout();
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = new WriterAppender(layout, os);
-        appender.setImmediateFlush(true);
-        appender.setThreshold(Level.INFO);
-        Logger zlogger = Logger.getLogger("org.apache.zookeeper");
-        zlogger.addAppender(appender);
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool("org.apache.zookeeper")) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
 
-        try {
             qu.shutdown(2);
             CountdownWatcher watcher = new CountdownWatcher();
             ZooKeeper zk = new ZooKeeper(qu.getConnString(), CONNECTION_TIMEOUT, watcher, true);
@@ -323,22 +313,21 @@ public class ReadOnlyModeTest extends ZKTestCase {
 
             // resume poor fellow
             qu.getPeer(1).peer.resume();
-        } finally {
-            zlogger.removeAppender(appender);
-        }
 
-        os.close();
-        LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
-        String line;
-        Pattern p = Pattern.compile(".*Majority server found.*");
-        boolean found = false;
-        while ((line = r.readLine()) != null) {
-            if (p.matcher(line).matches()) {
-                found = true;
-                break;
+            String log = os.toString();
+            assertFalse(StringUtils.isEmpty(log), "OutputStream doesn't have any log messages");
+
+            LineNumberReader r = new LineNumberReader(new StringReader(log));
+            String line;
+            Pattern p = Pattern.compile(".*Majority server found.*");
+            boolean found = false;
+            while ((line = r.readLine()) != null) {
+                if (p.matcher(line).matches()) {
+                    found = true;
+                    break;
+                }
             }
+            assertTrue(found, "Majority server wasn't found while connected to r/o server");
         }
-        assertTrue(found, "Majority server wasn't found while connected to r/o server");
     }
-
 }
diff --git a/zookeeper-server/src/test/java/org/apache/zookeeper/test/ReconfigExceptionTest.java b/zookeeper-server/src/test/java/org/apache/zookeeper/test/ReconfigExceptionTest.java
index aae69ad..9dc21ba 100644
--- a/zookeeper-server/src/test/java/org/apache/zookeeper/test/ReconfigExceptionTest.java
+++ b/zookeeper-server/src/test/java/org/apache/zookeeper/test/ReconfigExceptionTest.java
@@ -48,8 +48,8 @@ public class ReconfigExceptionTest extends ZKTestCase {
     // Use DigestAuthenticationProvider.base64Encode or
     // run ZooKeeper jar with org.apache.zookeeper.server.auth.DigestAuthenticationProvider to generate password.
     // An example:
-    // java -cp zookeeper-3.6.0-SNAPSHOT.jar:lib/log4j-1.2.17.jar:lib/slf4j-log4j12-1.7.5.jar:
-    // lib/slf4j-api-1.7.5.jar org.apache.zookeeper.server.auth.DigestAuthenticationProvider super:test
+    // java -cp zookeeper.jar:lib/slf4j-api-1.7.30.jar:lib/logback-classic-1.2.10.jar:lib/logback-core-1.2.10.jar:conf
+    // org.apache.zookeeper.server.auth.DigestAuthenticationProvider super:test
     // The password here is 'test'.
     private static String superDigest = "super:D/InIHSb7yEEbrWz8b9l71RjZJU=";
     private QuorumUtil qu;
diff --git a/zookeeper-server/src/test/resources/log4j.properties b/zookeeper-server/src/test/resources/log4j.properties
deleted file mode 100644
index 4a2ede9..0000000
--- a/zookeeper-server/src/test/resources/log4j.properties
+++ /dev/null
@@ -1,65 +0,0 @@
-# Copyright 2012 The Apache Software Foundation
-# 
-# Licensed to the Apache Software Foundation (ASF) under one
-# or more contributor license agreements.  See the NOTICE file
-# distributed with this work for additional information
-# regarding copyright ownership.  The ASF licenses this file
-# to you under the Apache License, Version 2.0 (the
-# "License"); you may not use this file except in compliance
-# with the License.  You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-# Define some default values that can be overridden by system properties
-zookeeper.root.logger=INFO, CONSOLE
-
-zookeeper.console.threshold=INFO
-
-zookeeper.log.dir=.
-zookeeper.log.file=zookeeper.log
-zookeeper.log.threshold=INFO
-zookeeper.log.maxfilesize=256MB
-zookeeper.log.maxbackupindex=20
-
-zookeeper.tracelog.dir=${zookeeper.log.dir}
-zookeeper.tracelog.file=zookeeper_trace.log
-
-log4j.rootLogger=${zookeeper.root.logger}
-
-#
-# console
-# Add "console" to rootlogger above if you want to use this 
-#
-log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
-log4j.appender.CONSOLE.Threshold=${zookeeper.console.threshold}
-log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
-log4j.appender.CONSOLE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n
-
-#
-# Add ROLLINGFILE to rootLogger to get log file output
-#
-log4j.appender.ROLLINGFILE=org.apache.log4j.RollingFileAppender
-log4j.appender.ROLLINGFILE.Threshold=${zookeeper.log.threshold}
-log4j.appender.ROLLINGFILE.File=${zookeeper.log.dir}/${zookeeper.log.file}
-log4j.appender.ROLLINGFILE.MaxFileSize=${zookeeper.log.maxfilesize}
-log4j.appender.ROLLINGFILE.MaxBackupIndex=${zookeeper.log.maxbackupindex}
-log4j.appender.ROLLINGFILE.layout=org.apache.log4j.PatternLayout
-log4j.appender.ROLLINGFILE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n
-
-#
-# Add TRACEFILE to rootLogger to get log file output
-#    Log TRACE level and above messages to a log file
-#
-log4j.appender.TRACEFILE=org.apache.log4j.FileAppender
-log4j.appender.TRACEFILE.Threshold=TRACE
-log4j.appender.TRACEFILE.File=${zookeeper.tracelog.dir}/${zookeeper.tracelog.file}
-
-log4j.appender.TRACEFILE.layout=org.apache.log4j.PatternLayout
-### Notice we are including log4j's NDC here (%x)
-log4j.appender.TRACEFILE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L][%x] - %m%n
diff --git a/zookeeper-server/src/test/resources/logback.xml b/zookeeper-server/src/test/resources/logback.xml
new file mode 100644
index 0000000..a1e6277
--- /dev/null
+++ b/zookeeper-server/src/test/resources/logback.xml
@@ -0,0 +1,36 @@
+<!--
+ Copyright 2022 The Apache Software Foundation
+
+ Licensed to the Apache Software Foundation (ASF) under one
+ or more contributor license agreements.  See the NOTICE file
+ distributed with this work for additional information
+ regarding copyright ownership.  The ASF licenses this file
+ to you under the Apache License, Version 2.0 (the
+ "License"); you may not use this file except in compliance
+ with the License.  You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+
+ Define some default values that can be overridden by system properties
+-->
+<configuration>
+
+  <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
+    <encoder>
+      <pattern>%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n</pattern>
+    </encoder>
+    <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
+      <level>INFO</level>
+    </filter>
+  </appender>
+
+  <root level="INFO">
+    <appender-ref ref="CONSOLE" />
+  </root>
+</configuration>