Zookeeper-服务器端启动流程(单机模式)

背景介绍

ZooKeeper可以以standalone,伪分布式和分布式三种方式部署.standalone模式下只有一台机器作为服务器,丧失了ZooKeeper高可用的特点.伪分布式是在一台电脑上使用不同端口启动多个ZooKeeper服务器.分布式是使用多个机器,每台机器上部署一个ZooKeeper服务器,即使有服务器宕机,只要少于半数,ZooKeeper集群依然可以正常对外提供服务.
ZooKeeper以standalone模式启动只需启动对客户端提供服务的组件,无需启动集群内部通信组件,较为简单,因此先从standalone模式开始介绍.

整体架构

Zookeeper整体架构如上图,其中包括ServerCnxnFactory,SessionTracker,RequestProcessor,FileTxnSnapLog等众多组件,这些组件都会在日后一一介绍.

启动流程概述

standalone模式启动主要包括如下几个步骤:

1. 配置文件解析
2. 创建并启动历史文件清理器
3. 初始化数据管理器
4. 注册shutdownHandler
5. 启动Admin server
6. 创建并启动网络IO管理器
7. 启动ZooKeeperServer
8. 创建并启动secureCnxnFactory
9. 创建并启动ContainerManager

源码如下:

    protected void initializeAndRun(String[] args)
            throws ConfigException, IOException, AdminServerException {
        //1.解析配置文件
        QuorumPeerConfig config = new QuorumPeerConfig();
        if (args.length == 1) {
            config.parse(args[0]);
        }

        // Start and schedule the the purge task
        //2.创建并启动历史文件清理器(对事务日志和快照数据文件进行定时清理)
        DatadirCleanupManager purgeMgr = new DatadirCleanupManager(config
                .getDataDir(), config.getDataLogDir(), config
                .getSnapRetainCount(), config.getPurgeInterval());
        purgeMgr.start();

        if (args.length == 1 && config.isDistributed()) {
            //集群启动
            runFromConfig(config);
        } else {
            //单机启动
            LOG.warn("Either no config or no quorum defined in config, running "
                    + " in standalone mode");
            // there is only server in the quorum -- run as standalone
            ZooKeeperServerMain.main(args);
        }
    }

    /**
     * Run from a ServerConfig.
     *
     * @param config ServerConfig to use.
     * @throws IOException
     * @throws AdminServerException
     */
    public void runFromConfig(ServerConfig config)
            throws IOException, AdminServerException {
        LOG.info("Starting server");
        FileTxnSnapLog txnLog = null;
        try {
            //3.创建ZooKeeper数据管理器
            txnLog = new FileTxnSnapLog(config.dataLogDir, config.dataDir);
            final ZooKeeperServer zkServer = new ZooKeeperServer(txnLog,
                    config.tickTime, config.minSessionTimeout, config.maxSessionTimeout, null);
            txnLog.setServerStats(zkServer.serverStats());

            //4.注册shutdownHandler,在ZooKeeperServer的状态变化时调用shutdownHandler的handle()
            final CountDownLatch shutdownLatch = new CountDownLatch(1);
            zkServer.registerServerShutdownHandler(
                    new ZooKeeperServerShutdownHandler(shutdow