[GitHub] [kafka] jsancio commented on a change in pull request #10019: MINOR: Introduce KafkaBroker trait for use in dynamic reconfiguration

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

jsancio commented on a change in pull request #10019:
URL: https://github.com/apache/kafka/pull/10019#discussion_r568242355



##########
File path: core/src/main/scala/kafka/server/DynamicBrokerConfig.scala
##########
@@ -669,7 +669,7 @@ class DynamicLogConfig(logManager: LogManager, server: KafkaServer) extends Brok
     updateLogsConfig(newBrokerDefaults.asScala)
 
     if (logManager.currentDefaultConfig.uncleanLeaderElectionEnable && !origUncleanLeaderElectionEnable) {
-      server.kafkaController.enableDefaultUncleanLeaderElection()
+      server.zkBasedKafkaController.foreach {_.enableDefaultUncleanLeaderElection() }

Review comment:
       It is idiomatic to use `()` instead of `{}` when the lambda is a single expression. E.g.
   ```scala
          server.zkBasedKafkaController.foreach(_.enableDefaultUncleanLeaderElection())
   ```

##########
File path: core/src/main/scala/kafka/server/DynamicBrokerConfig.scala
##########
@@ -936,7 +936,7 @@ class DynamicListenerConfig(server: KafkaServer) extends BrokerReconfigurable wi
     if (listenersAdded.nonEmpty)
       server.socketServer.addListeners(listenersAdded)
 
-    server.kafkaController.updateBrokerInfo(server.createBrokerInfo)
+    server.zkBasedKafkaController.foreach {_.updateBrokerInfo(server.createBrokerInfo) }

Review comment:
       It is idiomatic to use `()` instead of `{}` when the lambda is a single expression. E.g.
   ```scala
          server.zkBasedKafkaController.foreach(_.enableDefaultUncleanLeaderElection())
   ```

##########
File path: core/src/main/scala/kafka/server/KafkaBroker.scala
##########
@@ -0,0 +1,113 @@
+/**
+ * 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 kafka.server
+
+import java.util
+
+import com.yammer.metrics.{core => yammer}
+import kafka.controller.KafkaController
+import kafka.log.LogManager
+import kafka.metrics.{KafkaMetricsGroup, KafkaYammerMetrics, LinuxIoMetricsCollector}
+import kafka.network.SocketServer
+import kafka.utils.{KafkaScheduler, Logging}
+import kafka.zk.BrokerInfo
+import org.apache.kafka.clients.CommonClientConfigs
+import org.apache.kafka.common.ClusterResource
+import org.apache.kafka.common.internals.ClusterResourceListeners
+import org.apache.kafka.common.metrics.{KafkaMetricsContext, Metrics, MetricsReporter}
+import org.apache.kafka.common.utils.Time
+import org.apache.kafka.server.authorizer.Authorizer
+
+import scala.collection.Seq
+import scala.jdk.CollectionConverters._
+
+object KafkaBroker {
+  //properties for MetricsContext
+  val metricsPrefix: String = "kafka.server"
+  private val KAFKA_CLUSTER_ID: String = "kafka.cluster.id"
+  private val KAFKA_BROKER_ID: String = "kafka.broker.id"
+
+  private[server] def createKafkaMetricsContext(clusterId: String, config: KafkaConfig): KafkaMetricsContext = {
+    val contextLabels = new util.HashMap[String, Object]
+    contextLabels.put(KAFKA_CLUSTER_ID, clusterId)
+    contextLabels.put(KAFKA_BROKER_ID, config.brokerId.toString)
+    contextLabels.putAll(config.originalsWithPrefix(CommonClientConfigs.METRICS_CONTEXT_PREFIX))
+    val metricsContext = new KafkaMetricsContext(metricsPrefix, contextLabels)
+    metricsContext
+  }
+
+  private[server] def notifyClusterListeners(clusterId: String,
+                                             clusterListeners: Seq[AnyRef]): Unit = {
+    val clusterResourceListeners = new ClusterResourceListeners
+    clusterResourceListeners.maybeAddAll(clusterListeners.asJava)
+    clusterResourceListeners.onUpdate(new ClusterResource(clusterId))
+  }
+
+  private[server] def notifyMetricsReporters(clusterId: String,
+                                             config: KafkaConfig,
+                                             metricsReporters: Seq[AnyRef]): Unit = {
+    val metricsContext = createKafkaMetricsContext(clusterId, config)
+    metricsReporters.foreach {
+      case x: MetricsReporter => x.contextChange(metricsContext)
+      case _ => //do nothing
+    }
+  }
+}
+
+trait KafkaBroker extends Logging with KafkaMetricsGroup {

Review comment:
       Why does this trait extends `Logging` and `KafkaMetricsGroup`? These feel like an implementation detail.
   
   This looks like a very important trait and concept. Should we add documentation to all of the public methods?

##########
File path: core/src/main/scala/kafka/server/KafkaBroker.scala
##########
@@ -0,0 +1,113 @@
+/**
+ * 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 kafka.server
+
+import java.util
+
+import com.yammer.metrics.{core => yammer}
+import kafka.controller.KafkaController
+import kafka.log.LogManager
+import kafka.metrics.{KafkaMetricsGroup, KafkaYammerMetrics, LinuxIoMetricsCollector}
+import kafka.network.SocketServer
+import kafka.utils.{KafkaScheduler, Logging}
+import kafka.zk.BrokerInfo
+import org.apache.kafka.clients.CommonClientConfigs
+import org.apache.kafka.common.ClusterResource
+import org.apache.kafka.common.internals.ClusterResourceListeners
+import org.apache.kafka.common.metrics.{KafkaMetricsContext, Metrics, MetricsReporter}
+import org.apache.kafka.common.utils.Time
+import org.apache.kafka.server.authorizer.Authorizer
+
+import scala.collection.Seq
+import scala.jdk.CollectionConverters._
+
+object KafkaBroker {
+  //properties for MetricsContext
+  val metricsPrefix: String = "kafka.server"
+  private val KAFKA_CLUSTER_ID: String = "kafka.cluster.id"
+  private val KAFKA_BROKER_ID: String = "kafka.broker.id"
+
+  private[server] def createKafkaMetricsContext(clusterId: String, config: KafkaConfig): KafkaMetricsContext = {
+    val contextLabels = new util.HashMap[String, Object]
+    contextLabels.put(KAFKA_CLUSTER_ID, clusterId)
+    contextLabels.put(KAFKA_BROKER_ID, config.brokerId.toString)
+    contextLabels.putAll(config.originalsWithPrefix(CommonClientConfigs.METRICS_CONTEXT_PREFIX))
+    val metricsContext = new KafkaMetricsContext(metricsPrefix, contextLabels)
+    metricsContext
+  }
+
+  private[server] def notifyClusterListeners(clusterId: String,
+                                             clusterListeners: Seq[AnyRef]): Unit = {
+    val clusterResourceListeners = new ClusterResourceListeners
+    clusterResourceListeners.maybeAddAll(clusterListeners.asJava)
+    clusterResourceListeners.onUpdate(new ClusterResource(clusterId))
+  }
+
+  private[server] def notifyMetricsReporters(clusterId: String,
+                                             config: KafkaConfig,
+                                             metricsReporters: Seq[AnyRef]): Unit = {
+    val metricsContext = createKafkaMetricsContext(clusterId, config)
+    metricsReporters.foreach {
+      case x: MetricsReporter => x.contextChange(metricsContext)
+      case _ => //do nothing
+    }
+  }
+}
+
+trait KafkaBroker extends Logging with KafkaMetricsGroup {
+  def authorizer: Option[Authorizer]
+  def clusterId(): String
+  def config: KafkaConfig
+  def brokerState: BrokerState
+  def dataPlaneRequestHandlerPool: KafkaRequestHandlerPool
+  def kafkaScheduler: KafkaScheduler
+  def kafkaYammerMetrics: KafkaYammerMetrics
+  def logManager: LogManager
+  def metrics(): Metrics
+  def quotaManagers: QuotaFactory.QuotaManagers
+  def replicaManager: ReplicaManager
+  def socketServer: SocketServer
+
+  // must override the following in KafkaServer since they only apply there
+  def zkBasedKafkaController: Option[KafkaController] = None

Review comment:
       Ideally, we should not have a reference to ZooKeeper on a trait that is implemented by both the ZK quorum and Raft quorum. Maybe `kafkaController: Option[KafkaController]`.

##########
File path: core/src/main/scala/kafka/server/KafkaBroker.scala
##########
@@ -0,0 +1,113 @@
+/**
+ * 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 kafka.server
+
+import java.util
+
+import com.yammer.metrics.{core => yammer}
+import kafka.controller.KafkaController
+import kafka.log.LogManager
+import kafka.metrics.{KafkaMetricsGroup, KafkaYammerMetrics, LinuxIoMetricsCollector}
+import kafka.network.SocketServer
+import kafka.utils.{KafkaScheduler, Logging}
+import kafka.zk.BrokerInfo
+import org.apache.kafka.clients.CommonClientConfigs
+import org.apache.kafka.common.ClusterResource
+import org.apache.kafka.common.internals.ClusterResourceListeners
+import org.apache.kafka.common.metrics.{KafkaMetricsContext, Metrics, MetricsReporter}
+import org.apache.kafka.common.utils.Time
+import org.apache.kafka.server.authorizer.Authorizer
+
+import scala.collection.Seq
+import scala.jdk.CollectionConverters._
+
+object KafkaBroker {
+  //properties for MetricsContext
+  val metricsPrefix: String = "kafka.server"
+  private val KAFKA_CLUSTER_ID: String = "kafka.cluster.id"
+  private val KAFKA_BROKER_ID: String = "kafka.broker.id"
+
+  private[server] def createKafkaMetricsContext(clusterId: String, config: KafkaConfig): KafkaMetricsContext = {
+    val contextLabels = new util.HashMap[String, Object]
+    contextLabels.put(KAFKA_CLUSTER_ID, clusterId)
+    contextLabels.put(KAFKA_BROKER_ID, config.brokerId.toString)
+    contextLabels.putAll(config.originalsWithPrefix(CommonClientConfigs.METRICS_CONTEXT_PREFIX))
+    val metricsContext = new KafkaMetricsContext(metricsPrefix, contextLabels)
+    metricsContext
+  }
+
+  private[server] def notifyClusterListeners(clusterId: String,
+                                             clusterListeners: Seq[AnyRef]): Unit = {
+    val clusterResourceListeners = new ClusterResourceListeners
+    clusterResourceListeners.maybeAddAll(clusterListeners.asJava)
+    clusterResourceListeners.onUpdate(new ClusterResource(clusterId))
+  }
+
+  private[server] def notifyMetricsReporters(clusterId: String,
+                                             config: KafkaConfig,
+                                             metricsReporters: Seq[AnyRef]): Unit = {
+    val metricsContext = createKafkaMetricsContext(clusterId, config)
+    metricsReporters.foreach {
+      case x: MetricsReporter => x.contextChange(metricsContext)
+      case _ => //do nothing
+    }
+  }
+}
+
+trait KafkaBroker extends Logging with KafkaMetricsGroup {
+  def authorizer: Option[Authorizer]
+  def clusterId(): String
+  def config: KafkaConfig
+  def brokerState: BrokerState
+  def dataPlaneRequestHandlerPool: KafkaRequestHandlerPool
+  def kafkaScheduler: KafkaScheduler
+  def kafkaYammerMetrics: KafkaYammerMetrics
+  def logManager: LogManager
+  def metrics(): Metrics

Review comment:
       The methods `clusterId` and `metrics` have parenthesis `()` while the rest of the methods do not. Should we just remove the parenthesis for these methods? 

##########
File path: core/src/main/scala/kafka/server/KafkaBroker.scala
##########
@@ -0,0 +1,113 @@
+/**
+ * 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 kafka.server
+
+import java.util
+
+import com.yammer.metrics.{core => yammer}
+import kafka.controller.KafkaController
+import kafka.log.LogManager
+import kafka.metrics.{KafkaMetricsGroup, KafkaYammerMetrics, LinuxIoMetricsCollector}
+import kafka.network.SocketServer
+import kafka.utils.{KafkaScheduler, Logging}
+import kafka.zk.BrokerInfo
+import org.apache.kafka.clients.CommonClientConfigs
+import org.apache.kafka.common.ClusterResource
+import org.apache.kafka.common.internals.ClusterResourceListeners
+import org.apache.kafka.common.metrics.{KafkaMetricsContext, Metrics, MetricsReporter}
+import org.apache.kafka.common.utils.Time
+import org.apache.kafka.server.authorizer.Authorizer
+
+import scala.collection.Seq
+import scala.jdk.CollectionConverters._
+
+object KafkaBroker {
+  //properties for MetricsContext
+  val metricsPrefix: String = "kafka.server"
+  private val KAFKA_CLUSTER_ID: String = "kafka.cluster.id"
+  private val KAFKA_BROKER_ID: String = "kafka.broker.id"
+
+  private[server] def createKafkaMetricsContext(clusterId: String, config: KafkaConfig): KafkaMetricsContext = {
+    val contextLabels = new util.HashMap[String, Object]
+    contextLabels.put(KAFKA_CLUSTER_ID, clusterId)
+    contextLabels.put(KAFKA_BROKER_ID, config.brokerId.toString)
+    contextLabels.putAll(config.originalsWithPrefix(CommonClientConfigs.METRICS_CONTEXT_PREFIX))
+    val metricsContext = new KafkaMetricsContext(metricsPrefix, contextLabels)
+    metricsContext
+  }
+
+  private[server] def notifyClusterListeners(clusterId: String,
+                                             clusterListeners: Seq[AnyRef]): Unit = {
+    val clusterResourceListeners = new ClusterResourceListeners
+    clusterResourceListeners.maybeAddAll(clusterListeners.asJava)
+    clusterResourceListeners.onUpdate(new ClusterResource(clusterId))
+  }
+
+  private[server] def notifyMetricsReporters(clusterId: String,
+                                             config: KafkaConfig,
+                                             metricsReporters: Seq[AnyRef]): Unit = {
+    val metricsContext = createKafkaMetricsContext(clusterId, config)
+    metricsReporters.foreach {
+      case x: MetricsReporter => x.contextChange(metricsContext)
+      case _ => //do nothing
+    }
+  }
+}
+
+trait KafkaBroker extends Logging with KafkaMetricsGroup {
+  def authorizer: Option[Authorizer]
+  def clusterId(): String
+  def config: KafkaConfig
+  def brokerState: BrokerState
+  def dataPlaneRequestHandlerPool: KafkaRequestHandlerPool
+  def kafkaScheduler: KafkaScheduler
+  def kafkaYammerMetrics: KafkaYammerMetrics
+  def logManager: LogManager
+  def metrics(): Metrics
+  def quotaManagers: QuotaFactory.QuotaManagers
+  def replicaManager: ReplicaManager
+  def socketServer: SocketServer
+
+  // must override the following in KafkaServer since they only apply there
+  def zkBasedKafkaController: Option[KafkaController] = None
+  def createBrokerInfo: BrokerInfo = throw new UnsupportedOperationException("Unsupported in with a Raft-based meadata quorum")

Review comment:
       Why is "Raft-based" mentioned in generic `KafkaBroker` trait? Maybe we can remove the default implementation and force the classes implementing this trait to override the method.

##########
File path: core/src/main/scala/kafka/server/KafkaBroker.scala
##########
@@ -0,0 +1,113 @@
+/**
+ * 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 kafka.server
+
+import java.util
+
+import com.yammer.metrics.{core => yammer}
+import kafka.controller.KafkaController
+import kafka.log.LogManager
+import kafka.metrics.{KafkaMetricsGroup, KafkaYammerMetrics, LinuxIoMetricsCollector}
+import kafka.network.SocketServer
+import kafka.utils.{KafkaScheduler, Logging}
+import kafka.zk.BrokerInfo
+import org.apache.kafka.clients.CommonClientConfigs
+import org.apache.kafka.common.ClusterResource
+import org.apache.kafka.common.internals.ClusterResourceListeners
+import org.apache.kafka.common.metrics.{KafkaMetricsContext, Metrics, MetricsReporter}
+import org.apache.kafka.common.utils.Time
+import org.apache.kafka.server.authorizer.Authorizer
+
+import scala.collection.Seq
+import scala.jdk.CollectionConverters._
+
+object KafkaBroker {
+  //properties for MetricsContext
+  val metricsPrefix: String = "kafka.server"
+  private val KAFKA_CLUSTER_ID: String = "kafka.cluster.id"
+  private val KAFKA_BROKER_ID: String = "kafka.broker.id"
+
+  private[server] def createKafkaMetricsContext(clusterId: String, config: KafkaConfig): KafkaMetricsContext = {
+    val contextLabels = new util.HashMap[String, Object]
+    contextLabels.put(KAFKA_CLUSTER_ID, clusterId)
+    contextLabels.put(KAFKA_BROKER_ID, config.brokerId.toString)
+    contextLabels.putAll(config.originalsWithPrefix(CommonClientConfigs.METRICS_CONTEXT_PREFIX))
+    val metricsContext = new KafkaMetricsContext(metricsPrefix, contextLabels)
+    metricsContext
+  }
+
+  private[server] def notifyClusterListeners(clusterId: String,
+                                             clusterListeners: Seq[AnyRef]): Unit = {
+    val clusterResourceListeners = new ClusterResourceListeners
+    clusterResourceListeners.maybeAddAll(clusterListeners.asJava)
+    clusterResourceListeners.onUpdate(new ClusterResource(clusterId))
+  }

Review comment:
       This code is duplicated in `KafkaServer`.

##########
File path: core/src/main/scala/kafka/server/KafkaBroker.scala
##########
@@ -0,0 +1,113 @@
+/**
+ * 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 kafka.server
+
+import java.util
+
+import com.yammer.metrics.{core => yammer}
+import kafka.controller.KafkaController
+import kafka.log.LogManager
+import kafka.metrics.{KafkaMetricsGroup, KafkaYammerMetrics, LinuxIoMetricsCollector}
+import kafka.network.SocketServer
+import kafka.utils.{KafkaScheduler, Logging}
+import kafka.zk.BrokerInfo
+import org.apache.kafka.clients.CommonClientConfigs
+import org.apache.kafka.common.ClusterResource
+import org.apache.kafka.common.internals.ClusterResourceListeners
+import org.apache.kafka.common.metrics.{KafkaMetricsContext, Metrics, MetricsReporter}
+import org.apache.kafka.common.utils.Time
+import org.apache.kafka.server.authorizer.Authorizer
+
+import scala.collection.Seq
+import scala.jdk.CollectionConverters._
+
+object KafkaBroker {
+  //properties for MetricsContext
+  val metricsPrefix: String = "kafka.server"
+  private val KAFKA_CLUSTER_ID: String = "kafka.cluster.id"
+  private val KAFKA_BROKER_ID: String = "kafka.broker.id"
+
+  private[server] def createKafkaMetricsContext(clusterId: String, config: KafkaConfig): KafkaMetricsContext = {
+    val contextLabels = new util.HashMap[String, Object]
+    contextLabels.put(KAFKA_CLUSTER_ID, clusterId)
+    contextLabels.put(KAFKA_BROKER_ID, config.brokerId.toString)
+    contextLabels.putAll(config.originalsWithPrefix(CommonClientConfigs.METRICS_CONTEXT_PREFIX))
+    val metricsContext = new KafkaMetricsContext(metricsPrefix, contextLabels)
+    metricsContext
+  }
+
+  private[server] def notifyClusterListeners(clusterId: String,
+                                             clusterListeners: Seq[AnyRef]): Unit = {
+    val clusterResourceListeners = new ClusterResourceListeners
+    clusterResourceListeners.maybeAddAll(clusterListeners.asJava)
+    clusterResourceListeners.onUpdate(new ClusterResource(clusterId))
+  }
+
+  private[server] def notifyMetricsReporters(clusterId: String,
+                                             config: KafkaConfig,
+                                             metricsReporters: Seq[AnyRef]): Unit = {
+    val metricsContext = createKafkaMetricsContext(clusterId, config)
+    metricsReporters.foreach {
+      case x: MetricsReporter => x.contextChange(metricsContext)
+      case _ => //do nothing
+    }
+  }
+}
+
+trait KafkaBroker extends Logging with KafkaMetricsGroup {
+  def authorizer: Option[Authorizer]
+  def clusterId(): String
+  def config: KafkaConfig
+  def brokerState: BrokerState
+  def dataPlaneRequestHandlerPool: KafkaRequestHandlerPool
+  def kafkaScheduler: KafkaScheduler
+  def kafkaYammerMetrics: KafkaYammerMetrics
+  def logManager: LogManager
+  def metrics(): Metrics
+  def quotaManagers: QuotaFactory.QuotaManagers
+  def replicaManager: ReplicaManager
+  def socketServer: SocketServer
+
+  // must override the following in KafkaServer since they only apply there
+  def zkBasedKafkaController: Option[KafkaController] = None
+  def createBrokerInfo: BrokerInfo = throw new UnsupportedOperationException("Unsupported in with a Raft-based meadata quorum")
+
+
+  newKafkaServerGauge("BrokerState", () => brokerState.currentState)
+  newKafkaServerGauge("ClusterId", () => clusterId())
+  newKafkaServerGauge("yammer-metrics-count", () =>  KafkaYammerMetrics.defaultRegistry.allMetrics.size)
+
+  val linuxIoMetricsCollector = new LinuxIoMetricsCollector("/proc", Time.SYSTEM, logger.underlying)

Review comment:
       I think you can make this `private[this]`.
   
   If you want to make sure that these fields don't get leaked to implementing classes maybe we can move this default metric initialization to a companion object (static in Java) method:
   
   ```scala
   object KafkaBroker {
     def initializeDefaultMetrics(metricsGroup: KafkaMetricsGroup, kafkaServer: KafkaBroker): Unit
   }
   ```

##########
File path: core/src/main/scala/kafka/server/KafkaBroker.scala
##########
@@ -0,0 +1,113 @@
+/**
+ * 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 kafka.server
+
+import java.util
+
+import com.yammer.metrics.{core => yammer}
+import kafka.controller.KafkaController
+import kafka.log.LogManager
+import kafka.metrics.{KafkaMetricsGroup, KafkaYammerMetrics, LinuxIoMetricsCollector}
+import kafka.network.SocketServer
+import kafka.utils.{KafkaScheduler, Logging}
+import kafka.zk.BrokerInfo
+import org.apache.kafka.clients.CommonClientConfigs
+import org.apache.kafka.common.ClusterResource
+import org.apache.kafka.common.internals.ClusterResourceListeners
+import org.apache.kafka.common.metrics.{KafkaMetricsContext, Metrics, MetricsReporter}
+import org.apache.kafka.common.utils.Time
+import org.apache.kafka.server.authorizer.Authorizer
+
+import scala.collection.Seq
+import scala.jdk.CollectionConverters._
+
+object KafkaBroker {
+  //properties for MetricsContext
+  val metricsPrefix: String = "kafka.server"
+  private val KAFKA_CLUSTER_ID: String = "kafka.cluster.id"
+  private val KAFKA_BROKER_ID: String = "kafka.broker.id"
+
+  private[server] def createKafkaMetricsContext(clusterId: String, config: KafkaConfig): KafkaMetricsContext = {
+    val contextLabels = new util.HashMap[String, Object]
+    contextLabels.put(KAFKA_CLUSTER_ID, clusterId)
+    contextLabels.put(KAFKA_BROKER_ID, config.brokerId.toString)
+    contextLabels.putAll(config.originalsWithPrefix(CommonClientConfigs.METRICS_CONTEXT_PREFIX))
+    val metricsContext = new KafkaMetricsContext(metricsPrefix, contextLabels)
+    metricsContext
+  }
+
+  private[server] def notifyClusterListeners(clusterId: String,
+                                             clusterListeners: Seq[AnyRef]): Unit = {
+    val clusterResourceListeners = new ClusterResourceListeners
+    clusterResourceListeners.maybeAddAll(clusterListeners.asJava)
+    clusterResourceListeners.onUpdate(new ClusterResource(clusterId))
+  }
+
+  private[server] def notifyMetricsReporters(clusterId: String,
+                                             config: KafkaConfig,
+                                             metricsReporters: Seq[AnyRef]): Unit = {
+    val metricsContext = createKafkaMetricsContext(clusterId, config)
+    metricsReporters.foreach {
+      case x: MetricsReporter => x.contextChange(metricsContext)
+      case _ => //do nothing
+    }
+  }

Review comment:
       This code is duplicated in `KafkaServer`.




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