flume【源码分析】分析Flume的启动过程

前言

之前一直在用flume收集数据，也做了一些插件开发，但是一直没整理相关的知识，最近感觉老是有一种知其然不知其所以然的感觉，所以从源码入手希望能更透彻一点吧，越来越感觉会用不能掌握啊！别人几个为啥就low了！

1.启动入口

估计没人关注过启动入口在什么地方吧?启动不报错就可以直接去用了吧！

从这里可以看出flume的启动入口是：org.apache.flume.node.Application 注意：记得用maven 安装flume-ng-node 不然你找不到！因为有的开发用不到也就不装了！

下面我们就来看该入口程序是如何来运行的：

try {

      boolean isZkConfigured = false;

      Options options = new Options();

      Option option = new Option("n", "name", true, "the name of this agent");
      option.setRequired(true);
      options.addOption(option);

      option = new Option("f", "conf-file", true,
          "specify a config file (required if -z missing)");
      option.setRequired(false);
      options.addOption(option);

      option = new Option(null, "no-reload-conf", false,
          "do not reload config file if changed");
      options.addOption(option);

      // Options for Zookeeper
      option = new Option("z", "zkConnString", true,
          "specify the ZooKeeper connection to use (required if -f missing)");
      option.setRequired(false);
      options.addOption(option);

      option = new Option("p", "zkBasePath", true,
          "specify the base path in ZooKeeper for agent configs");
      option.setRequired(false);
      options.addOption(option);

      option = new Option("h", "help", false, "display help text");
      options.addOption(option);

      CommandLineParser parser = new GnuParser();
      CommandLine commandLine = parser.parse(options, args);

      if (commandLine.hasOption('h')) {
        new HelpFormatter().printHelp("flume-ng agent", options, true);
        return;
      }

      String agentName = commandLine.getOptionValue('n');
      boolean reload = !commandLine.hasOption("no-reload-conf");

      if (commandLine.hasOption('z') || commandLine.hasOption("zkConnString")) {
        isZkConfigured = true;
      }
      Application application = null;
      if (isZkConfigured) {
        // get options
        String zkConnectionStr = commandLine.getOptionValue('z');
        String baseZkPath = commandLine.getOptionValue('p');

        if (reload) {
          EventBus eventBus = new EventBus(agentName + "-event-bus");
          List<LifecycleAware> components = Lists.newArrayList();
          PollingZooKeeperConfigurationProvider zookeeperConfigurationProvider =
            new PollingZooKeeperConfigurationProvider(
              agentName, zkConnectionStr, baseZkPath, eventBus);
          components.add(zookeeperConfigurationProvider);
          application = new Application(components);
          eventBus.register(application);
        } else {
          StaticZooKeeperConfigurationProvider zookeeperConfigurationProvider =
            new StaticZooKeeperConfigurationProvider(
              agentName, zkConnectionStr, baseZkPath);
          application = new Application();
          application.handleConfigurationEvent(zookeeperConfigurationProvider
            .getConfiguration());
        }
      } else {
        File configurationFile = new File(commandLine.getOptionValue('f'));

        /*
         * The following is to ensure that by default the agent will fail on
         * startup if the file does not exist.
         */
        if (!configurationFile.exists()) {
          // If command line invocation, then need to fail fast
          if (System.getProperty(Constants.SYSPROP_CALLED_FROM_SERVICE) ==
            null) {
            String path = configurationFile.getPath();
            try {
              path = configurationFile.getCanonicalPath();
            } catch (IOException ex) {
              logger.error("Failed to read canonical path for file: " + path,
                ex);
            }
            throw new ParseException(
              "The specified configuration file does not exist: " + path);
          }
        }
        List<LifecycleAware> components = Lists.newArrayList();

        if (reload) {
          EventBus eventBus = new EventBus(agentName + "-event-bus");
          PollingPropertiesFileConfigurationProvider configurationProvider =
            new PollingPropertiesFileConfigurationProvider(
              agentName, configurationFile, eventBus, 30);
          components.add(configurationProvider);
          application = new Application(components);
          eventBus.register(application);
        } else {
          PropertiesFileConfigurationProvider configurationProvider =
            new PropertiesFileConfigurationProvider(
              agentName, configurationFile);
          application = new Application();
          application.handleConfigurationEvent(configurationProvider
            .getConfiguration());
        }
      }
      application.start();

      final Application appReference = application;
      Runtime.getRuntime().addShutdownHook(new Thread("agent-shutdown-hook") {
        @Override
        public void run() {
          appReference.stop();
        }
      });

    } catch (Exception e) {
      logger.error("A fatal error occurred while running. Exception follows.",
          e);
    }
  }

附：flume每次启动都会先判断有没有与当前配置的三大组件同名的组件存在，存在的话先停掉该组件，顺序为source，sink，channel

其次是启动所有当前配置的组件，启动顺序为channel，sink，source

以上启动顺序来源如下：

public synchronized void handleConfigurationEvent(MaterializedConfiguration conf) {  
    stopAllComponents();  
    startAllComponents(conf);  
  } 

这个地方说几句：

1.前面一堆就是启动命令中一些参数的解析，如果真想了解自己去看看源码吧！

2.这里面有两种形式配置文件,一种是连接zk读取配置文件的，一种是读取配置文件，反正我经常用的也是读取配置文件的方式-f 那就说配置文件吧！

3.这里有一个机制，如果不带--no-reload-conf这个参数，flume会自动加载配置参数 默认是30秒，现在不用再傻傻的修改完配置文件去重启flume了吧！

        if (reload) {
          EventBus eventBus = new EventBus(agentName + "-event-bus");
          PollingPropertiesFileConfigurationProvider configurationProvider =
            new PollingPropertiesFileConfigurationProvider(
              agentName, configurationFile, eventBus, 30);
          components.add(configurationProvider);
          application = new Application(components);
          eventBus.register(application);
        } else {
          PropertiesFileConfigurationProvider configurationProvider =
            new PropertiesFileConfigurationProvider(
              agentName, configurationFile);
          application = new Application();
          application.handleConfigurationEvent(configurationProvider
            .getConfiguration());
        }

PollingPropertiesFileConfigurationProvider该类是一个轮询操作，每隔30秒会去检查conf配置文件。

这个地方如果不是轮训的方式，那么需要杀掉所有组件，在重启所有组件。调用这两个方法 stopAllComponents(); startAllComponents(conf);

configurationProvider.getConfiguration() 这个是重点好多配置，source 类型，source 和channel对接都在这个里面

1.请注意重点看一下loadxx方法

2.loadSources里面有个 SourceRunner.forSource(source)是指定source类型的：PollableSource，EventDrivenSourceRunner这个需要你在自己开发的时候根据需求自己继承吧！

  public static SourceRunner forSource(Source source) {
    SourceRunner runner = null;

    if (source instanceof PollableSource) {
      runner = new PollableSourceRunner();
      ((PollableSourceRunner) runner).setSource((PollableSource) source);
    } else if (source instanceof EventDrivenSource) {
      runner = new EventDrivenSourceRunner();
      ((EventDrivenSourceRunner) runner).setSource((EventDrivenSource) source);
    } else {
      throw new IllegalArgumentException("No known runner type for source "
          + source);
    }

    return runner;
  }

public MaterializedConfiguration getConfiguration() {
    MaterializedConfiguration conf = new SimpleMaterializedConfiguration();
    FlumeConfiguration fconfig = getFlumeConfiguration();
    AgentConfiguration agentConf = fconfig.getConfigurationFor(getAgentName());
    if (agentConf != null) {
      Map<String, ChannelComponent> channelComponentMap = Maps.newHashMap();
      Map<String, SourceRunner> sourceRunnerMap = Maps.newHashMap();
      Map<String, SinkRunner> sinkRunnerMap = Maps.newHashMap();
      try {
        loadChannels(agentConf, channelComponentMap);
        loadSources(agentConf, channelComponentMap, sourceRunnerMap);
        loadSinks(agentConf, channelComponentMap, sinkRunnerMap);
        Set<String> channelNames =
            new HashSet<String>(channelComponentMap.keySet());
        for(String channelName : channelNames) {
          ChannelComponent channelComponent = channelComponentMap.
              get(channelName);
          if(channelComponent.components.isEmpty()) {
            LOGGER.warn(String.format("Channel %s has no components connected" +
                " and has been removed.", channelName));
            channelComponentMap.remove(channelName);
            Map<String, Channel> nameChannelMap = channelCache.
                get(channelComponent.channel.getClass());
            if(nameChannelMap != null) {
              nameChannelMap.remove(channelName);
            }
          } else {
            LOGGER.info(String.format("Channel %s connected to %s",
                channelName, channelComponent.components.toString()));
            conf.addChannel(channelName, channelComponent.channel);
          }
        }
        for(Map.Entry<String, SourceRunner> entry : sourceRunnerMap.entrySet()) {
          conf.addSourceRunner(entry.getKey(), entry.getValue());
        }
        for(Map.Entry<String, SinkRunner> entry : sinkRunnerMap.entrySet()) {
          conf.addSinkRunner(entry.getKey(), entry.getValue());
        }
      } catch (InstantiationException ex) {
        LOGGER.error("Failed to instantiate component", ex);
      } finally {
        channelComponentMap.clear();
        sourceRunnerMap.clear();
        sinkRunnerMap.clear();
      }
    } else {
      LOGGER.warn("No configuration found for this host:{}", getAgentName());
    }
    return conf;
  }

这里通过文件修改时间来判断是否配置文件被修改了，然后通过事件总线的post调用EventHandler，也就是被@Subscribe注解的方法：这个地方只需要添加这个注解就可以就会指定调用方法执行了。

@Subscribe  
  public synchronized void handleConfigurationEvent(MaterializedConfiguration conf) {  
    stopAllComponents();  
    startAllComponents(conf);  
  }

2.前面配置准备完后启动程序

启动程序：application.start();

  public synchronized void start() {
    for(LifecycleAware component : components) {
      supervisor.supervise(component,
          new SupervisorPolicy.AlwaysRestartPolicy(), LifecycleState.START);
    }
  }

这是对所有组件进行监督supervise，只有在flume启动或者配置发生更改的时候会调用此监督方法

MonitorRunnable monitorRunnable = new MonitorRunnable();  
    monitorRunnable.lifecycleAware = lifecycleAware;  
    monitorRunnable.supervisoree = process;  
    monitorRunnable.monitorService = monitorService;  
  
    supervisedProcesses.put(lifecycleAware, process);  
  
    ScheduledFuture<?> future = monitorService.scheduleWithFixedDelay(  
        monitorRunnable, 0, 3, TimeUnit.SECONDS);  
    monitorFutures.put(lifecycleAware, future); 

方法里将每个组件纳入了生命周期的管理中，每隔3秒会执行以下方法【在停止组件的时候，会调用unsupervisor方法，会给各个组件状态赋值】：

1、判断组件状态

2、如果组件当前状态不是组件预期的状态，那么就要对预期状态按照switch分支来执行相应的逻辑

MonitorRunnable 继承了Runnable接口，重写了run方法！

    @Override
    public void run() {
      logger.debug("checking process:{} supervisoree:{}", lifecycleAware,
          supervisoree);

      long now = System.currentTimeMillis();

      try {
        if (supervisoree.status.firstSeen == null) {
          logger.debug("first time seeing {}", lifecycleAware);

          supervisoree.status.firstSeen = now;
        }

        supervisoree.status.lastSeen = now;
        synchronized (lifecycleAware) {
          if (supervisoree.status.discard) {
            // Unsupervise has already been called on this.
            logger.info("Component has already been stopped {}", lifecycleAware);
            return;
          } else if (supervisoree.status.error) {
            logger.info("Component {} is in error state, and Flume will not"
                + "attempt to change its state", lifecycleAware);
            return;
          }

          supervisoree.status.lastSeenState = lifecycleAware.getLifecycleState();

          if (!lifecycleAware.getLifecycleState().equals(
              supervisoree.status.desiredState)) {

            logger.debug("Want to transition {} from {} to {} (failures:{})",
                new Object[] { lifecycleAware, supervisoree.status.lastSeenState,
                    supervisoree.status.desiredState,
                    supervisoree.status.failures });

            switch (supervisoree.status.desiredState) {
              case START:
                try {
                  lifecycleAware.start();
                } catch (Throwable e) {
                  logger.error("Unable to start " + lifecycleAware
                      + " - Exception follows.", e);
                  if (e instanceof Error) {
                    // This component can never recover, shut it down.
                    supervisoree.status.desiredState = LifecycleState.STOP;
                    try {
                      lifecycleAware.stop();
                      logger.warn("Component {} stopped, since it could not be"
                          + "successfully started due to missing dependencies",
                          lifecycleAware);
                    } catch (Throwable e1) {
                      logger.error("Unsuccessful attempt to "
                          + "shutdown component: {} due to missing dependencies."
                          + " Please shutdown the agent"
                          + "or disable this component, or the agent will be"
                          + "in an undefined state.", e1);
                      supervisoree.status.error = true;
                      if (e1 instanceof Error) {
                        throw (Error) e1;
                      }
                      // Set the state to stop, so that the conf poller can
                      // proceed.
                    }
                  }
                  supervisoree.status.failures++;
                }
                break;
              case STOP:
                try {
                  lifecycleAware.stop();
                } catch (Throwable e) {
                  logger.error("Unable to stop " + lifecycleAware
                      + " - Exception follows.", e);
                  if (e instanceof Error) {
                    throw (Error) e;
                  }
                  supervisoree.status.failures++;
                }
                break;
              default:
                logger.warn("I refuse to acknowledge {} as a desired state",
                    supervisoree.status.desiredState);
            }

            if (!supervisoree.policy.isValid(lifecycleAware, supervisoree.status)) {
              logger.error(
                  "Policy {} of {} has been violated - supervisor should exit!",
                  supervisoree.policy, lifecycleAware);
            }
          }
        }
      } catch(Throwable t) {
        logger.error("Unexpected error", t);
      }
      logger.debug("Status check complete");
    }

注意：lifecycleAware.start(); 这个才是所有的核心,当判断状态后开始调用相关的start()方法。