Kafka启动的流程

调用KafkaServer的startup方法启动kafka

 /**
   * Start up API for bringing up a single instance of the Kafka server.
   * Instantiates the LogManager, the SocketServer and the request handlers - KafkaRequestHandlers
   */
  def startup() {
    try {
      info("starting")
      brokerState.newState(Starting)
      isShuttingDown = new AtomicBoolean(false)
      shutdownLatch = new CountDownLatch(1)

      /* start scheduler */
      kafkaScheduler.startup()
    
      /* setup zookeeper */
      zkClient = initZk()

      /* start log manager */
      logManager = createLogManager(zkClient, brokerState)
      logManager.startup()
      //socket server接收请求，和处理请求
      socketServer = new SocketServer(config.brokerId,
                                      config.hostName,
                                      config.port,
                                      config.numNetworkThreads,
                                      config.queuedMaxRequests,
                                      config.socketSendBufferBytes,
                                      config.socketReceiveBufferBytes,
                                      config.socketRequestMaxBytes,
                                      config.maxConnectionsPerIp,
                                      config.connectionsMaxIdleMs,
                                      config.maxConnectionsPerIpOverrides)
      socketServer.startup()
      //replicat manager，负责写多个副本
      replicaManager = new ReplicaManager(config, time, zkClient, kafkaScheduler, logManager, isShuttingDown)

      /* start offset manager */
      offsetManager = createOffsetManager()
      //kafka controller，相当于master,用于协调管理，kafka的master和broker合在一起，不用单独部署
      kafkaController = new KafkaController(config, zkClient, brokerState)
    
      /* start processing requests */
      apis = new KafkaApis(socketServer.requestChannel, replicaManager, offsetManager, zkClient, config.brokerId, config, kafkaController)
     //请求处理线程池 
     requestHandlerPool = new KafkaRequestHandlerPool(config.brokerId, socketServer.requestChannel, apis, config.numIoThreads)
      brokerState.newState(RunningAsBroker)
   
      Mx4jLoader.maybeLoad()

      replicaManager.startup()

      kafkaController.startup()
      
      //用于监控配置信息的变更
      topicConfigManager = new TopicConfigManager(zkClient, logManager)
      topicConfigManager.startup()
    
      /* tell everyone we are alive */
      kafkaHealthcheck = new KafkaHealthcheck(config.brokerId, config.advertisedHostName, config.advertisedPort, config.zkSessionTimeoutMs, zkClient)
      kafkaHealthcheck.startup()

    
      registerStats()
      startupComplete.set(true)
      info("started")
    }
    catch {
      case e: Throwable =>
        fatal("Fatal error during KafkaServer startup. Prepare to shutdown", e)
        shutdown()
        throw e
    }
  }