[GitHub] [hbase] ndimiduk commented on a diff in pull request #4691: HBASE-20904 Prometheus /metrics http endpoint for monitoring

[GitBox <gi...@apache.org>]

ndimiduk commented on code in PR #4691:
URL: https://github.com/apache/hbase/pull/4691#discussion_r953603702


##########
hbase-http/src/main/java/org/apache/hadoop/hbase/http/prometheus/PrometheusHadoopServlet.java:
##########
@@ -0,0 +1,84 @@
+/*
+ * 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.hadoop.hbase.http.prometheus;
+
+import com.google.errorprone.annotations.RestrictedApi;
+import java.io.IOException;
+import java.io.Writer;
+import java.util.Collection;
+import java.util.regex.Pattern;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import org.apache.commons.lang3.StringUtils;
+import org.apache.hadoop.metrics2.AbstractMetric;
+import org.apache.hadoop.metrics2.MetricType;
+import org.apache.hadoop.metrics2.MetricsRecord;
+import org.apache.hadoop.metrics2.MetricsTag;
+import org.apache.hadoop.metrics2.impl.MetricsExportHelper;
+import org.apache.yetus.audience.InterfaceAudience;
+
+@InterfaceAudience.Private
+public class PrometheusHadoopServlet extends HttpServlet {

Review Comment:
   Why is this called a "Hadoop" servlet?



##########
hbase-http/src/main/java/org/apache/hadoop/hbase/http/prometheus/PrometheusHadoopServlet.java:
##########
@@ -0,0 +1,84 @@
+/*
+ * 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.hadoop.hbase.http.prometheus;
+
+import com.google.errorprone.annotations.RestrictedApi;
+import java.io.IOException;
+import java.io.Writer;
+import java.util.Collection;
+import java.util.regex.Pattern;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import org.apache.commons.lang3.StringUtils;
+import org.apache.hadoop.metrics2.AbstractMetric;
+import org.apache.hadoop.metrics2.MetricType;
+import org.apache.hadoop.metrics2.MetricsRecord;
+import org.apache.hadoop.metrics2.MetricsTag;
+import org.apache.hadoop.metrics2.impl.MetricsExportHelper;
+import org.apache.yetus.audience.InterfaceAudience;
+
+@InterfaceAudience.Private
+public class PrometheusHadoopServlet extends HttpServlet {

Review Comment:
   Oh no, why was this implemented as a raw servlet :'(
   
   We have Jersey. There is absolutely no reason to implement a servlet by hand.



##########
hbase-http/src/main/java/org/apache/hadoop/hbase/http/HttpServer.java:
##########
@@ -784,6 +787,22 @@ protected void addDefaultServlets(ContextHandlerCollection contexts, Configurati
       LOG.info("ASYNC_PROFILER_HOME environment variable and async.profiler.home system property "
         + "not specified. Disabling /prof endpoint.");
     }
+
+    /* register metrics servlets */
+    String[] enabledServlets = conf.getStrings(METRIC_SERVLETS_CONF_KEY, METRICS_SERVLETS_DEFAULT);
+    for (String enabledServlet : enabledServlets) {
+      try {
+        ServletConfig servletConfig = METRIC_SERVLETS.get(enabledServlet);
+        if (servletConfig != null) {
+          Class<?> clz = Class.forName(servletConfig.getClazz());
+          addPrivilegedServlet(servletConfig.getName(), servletConfig.getPathSpec(),
+            clz.asSubclass(HttpServlet.class));
+        }
+      } catch (Exception e) {
+        /* shouldn't be fatal, so warn the user about it */

Review Comment:
   I'm surprised that having metrics be optional was accepted by review. Before this change, it was impossible to run an HBase processes that exposes no metrics at all. Now, that can happen. We do not have other healthcheck endpoints like a modern web service, metrics are the only lifeline for an operations team (besides inspecting the pid). I think that we should be more careful here:
   * we should warn if the process is configured without any metrics endpoint
   * we should warn if a configured metric endpoint fails to load
   * we should abort the process launch if the process is configured with any metrics but none load



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