Flume采用zookeeper管理配置

Flume支持通过zookeeper来管理Agent的配置，但是这是一个实验性的功能。配置文件必须先上传到zookeeper中。以下Agent在Zookeeper节点树的结构：

- /flume
 |- /a1 [Agent配置文件]
 |- /a2 [Agent配置文件]

处理配置文件的类：

org.apache.flume.node.PollingZooKeeperConfigurationProvider ： 如果zookeeper指定的路径有变更，就从Zookeeper重新获取配置文件。
org.apache.flume.node.StaticZooKeeperConfigurationProvider ： 启动Flume后，不会重新加载配置文件，即使Zookeeper的配置文件有变更。
org.apache.flume.agent.embedded.MemoryConfigurationProvider ： 从存储中读取配置文件。传入数据格式是Map。
org.apache.flume.node.PollingPropertiesFileConfigurationProvider ： 定时冲硬盘读取配置文件。

org.apache.flume.node.AbstractZooKeeperConfigurationProvider创建Zookeeper客户端：

  protected CuratorFramework createClient() {
    return CuratorFrameworkFactory.newClient(zkConnString,
        new ExponentialBackoffRetry(1000, 1));
  }

Flume采用Curator作为zookeeper的客户端，Curator是Netflix公司开源的一个Zookeeper客户端，与Zookeeper提供的原生客户端相比，Curator的抽象层次更高，简化了Zookeeper客户端的开发量。

Curator的maven配置：

    org.apache.curator
    apache-curator
    2.9.0

Zookeeper还有一个原生态的客户端，maven配置：

    org.apache.zookeeper
    zookeeper
    3.4.6

使用原生态的客户端，上传配置文件flume-zookeeper.properties到zookeeper集群：

	@Test
	public void uploadFileToZK() throws KeeperException, InterruptedException {
		String propFilePath = "D:\\flume-zookeeper.properties";

		ZooKeeper zk = null;
		try {
			zk = new ZooKeeper("10.0.1.85:2181,10.0.1.86:2181,10.0.1.87:2181", 300000, new Watcher() {
				// 监控所有被触发的事件
				public void process(WatchedEvent event) {
					System.out.println("已经触发了" + event.getType() + "事件！");
				}
			});
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		if (zk.exists("/flume", true) == null) {
			zk.create("/flume", null, Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
		}
		InputStream is = null;
		ByteArrayOutputStream bytestream = null;
		byte[] data = null;
		try {
			is = new FileInputStream(propFilePath);
			bytestream = new ByteArrayOutputStream();
			int ch;
			while ((ch = is.read()) != -1) {
				bytestream.write(ch);
			}
			data = bytestream.toByteArray();
			System.out.println(new String(data));
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			try {
				bytestream.close();
				is.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}

		// 创建一个目录节点
		Stat stat = zk.exists("/flume/a1", true);
		if (stat == null) {
			zk.create("/flume/a1", data, Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
		} else {
			zk.delete("/flume/a1", stat.getVersion());
			zk.create("/flume/a1", data, Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
		}
	}

	@Test
	public void get() throws KeeperException, InterruptedException {
		ZooKeeper zk = null;
		try {
			zk = new ZooKeeper("10.0.1.85:2181,10.0.1.86:2181,10.0.1.87:2181", 300000, new Watcher() {
				// 监控所有被触发的事件
				public void process(WatchedEvent event) {
					System.out.println("已经触发了" + event.getType() + "事件！");
				}
			});
		} catch (IOException e) {
			e.printStackTrace();
		}
		System.out.println(new String(zk.getData("/flume/a1", true, null)));
	}

flume-zookeeper.properties 配置文件内容：

a1.channels.c1.type = memory
a1.channels.c1.capacity = 1000
a1.channels.c1.transactionCapacity = 100
      
a1.sources.r1.channels = c1
a1.sources.r1.type = AVRO
a1.sources.r1.bind = 0.0.0.0
a1.sources.r1.port = 41414 

a1.sinks.k1.channel = c1
a1.sinks.k1.type = file_roll
a1.sinks.k1.sink.directory = /logs/
a1.sinks.k1.sink.rollInterval = 0

a1.channels = c1
a1.sources = r1
a1.sinks = k1

avro获取数据，通过Memory Channel写入文件中。

配置文件上传到Zookeeper后，通过如下命令启动Flume：

$ bin/flume-ng agent –conf conf -z 10.0.1.85:2181,10.0.1.86:2181,10.0.1.87:2181 -p /flume –name a1 -Dflume.root.logger=INFO,console

参数名称	默认值	描述
z	–	Zookeeper的连接字符串hostname:port列表通过逗号分隔。
p	/flume	Agent配置文件的根路径。

zookeeper中的配置如果有更新，Flume会通过PollingZooKeeperConfigurationProvider类的 refreshConfiguration 方法重新加载配置：

private void refreshConfiguration() throws IOException {
    LOGGER.info("Refreshing configuration from ZooKeeper");
    byte[] data = null;
    ChildData childData = agentNodeCache.getCurrentData();
    if (childData != null) {
      data = childData.getData();
    }
    flumeConfiguration = configFromBytes(data);
    eventBus.post(getConfiguration());
  }