zk的启动模式分为单机模式和集群模式，本文分析的是单机模式下的zk启动过程。无论是单机模式还是集群模式，通过zkServer.sh，我们知道它的入口类都是org.apache.zookeeper.server.quorum.QuorumPeerMain。
从QuorumPeerMain的main类方法入手
public static void main(String[] args) {
QuorumPeerMain main = new QuorumPeerMain();
try {
main.initializeAndRun(args);
} catch (IllegalArgumentException e) {
LOG.error("Invalid arguments, exiting abnormally", e);
LOG.info(USAGE);
System.err.println(USAGE);
ZKAuditProvider.addServerStartFailureAuditLog();
ServiceUtils.requestSystemExit(ExitCode.INVALID_INVOCATION.getValue());
} catch (ConfigException e) {
LOG.error("Invalid config, exiting abnormally", e);
System.err.println("Invalid config, exiting abnormally");
ZKAuditProvider.addServerStartFailureAuditLog();
ServiceUtils.requestSystemExit(ExitCode.INVALID_INVOCATION.getValue());
} catch (DatadirException e) {
LOG.error("Unable to access datadir, exiting abnormally", e);
System.err.println("Unable to access datadir, exiting abnormally");
ZKAuditProvider.addServerStartFailureAuditLog();
ServiceUtils.requestSystemExit(ExitCode.UNABLE_TO_ACCESS_DATADIR.getValue());
} catch (AdminServerException e) {
LOG.error("Unable to start AdminServer, exiting abnormally", e);
System.err.println("Unable to start AdminServer, exiting abnormally");
ZKAuditProvider.addServerStartFailureAuditLog();
ServiceUtils.requestSystemExit(ExitCode.ERROR_STARTING_ADMIN_SERVER.getValue());
} catch (Exception e) {
LOG.error("Unexpected exception, exiting abnormally", e);
ZKAuditProvider.addServerStartFailureAuditLog();
ServiceUtils.requestSystemExit(ExitCode.UNEXPECTED_ERROR.getValue());
}
LOG.info("Exiting normally");
ServiceUtils.requestSystemExit(ExitCode.EXECUTION_FINISHED.getValue());
}
这个方法的主要逻辑是初始化一个本类的对象，并调用它的initializeAndRun，并将命令行参数传递过去。ZKAuditProvider提供审计日志的功能，ServiceUtils.requestSystemExit打印一条日志并通过System.exit退出程序。
接下来看QuorumPeerMain的initializeAndRun成员方法
protected void initializeAndRun(String[] args) throws ConfigException, IOException, AdminServerException {
QuorumPeerConfig config = new QuorumPeerConfig();
if (args.length == 1) {
config.parse(args[0]);
}
// Start and schedule the the purge task
DatadirCleanupManager purgeMgr = new DatadirCleanupManager(
config.getDataDir(),
config.getDataLogDir(),
config.getSnapRetainCount(),
config.getPurgeInterval());
purgeMgr.start();
if (args.length == 1 && config.isDistributed()) {
runFromConfig(config);
} else {
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);
}
}
主要包含以下步骤：
- 判断命令行参数的数目，若只有一个，将其视为配置文件名并加载配置。
- 初始化数据目录清理定时任务并开始。
- 判断处于单机模式还是集群模式，我们这里暂时只分析单机模式。单机模式下调用ZooKeeperServerMain的main方法，并将命令行参数传递过去。
接下来分析ZooKeeperServerMain类。
进入ZooKeeperServerMain的main类方法
public static void main(String[] args) {
ZooKeeperServerMain main = new ZooKeeperServerMain();
try {
main.initializeAndRun(args);
} catch (IllegalArgumentException e) {
LOG.error("Invalid arguments, exiting abnormally", e);
LOG.info(USAGE);
System.err.println(USAGE);
ZKAuditProvider.addServerStartFailureAuditLog();
ServiceUtils.requestSystemExit(ExitCode.INVALID_INVOCATION.getValue());
} catch (ConfigException e) {
LOG.error("Invalid config, exiting abnormally", e);
System.err.println("Invalid config, exiting abnormally");
ZKAuditProvider.addServerStartFailureAuditLog();
ServiceUtils.requestSystemExit(ExitCode.INVALID_INVOCATION.getValue());
} catch (DatadirException e) {
LOG.error("Unable to access datadir, exiting abnormally", e);
System.err.println("Unable to access datadir, exiting abnormally");
ZKAuditProvider.addServerStartFailureAuditLog();
ServiceUtils.requestSystemExit(ExitCode.UNABLE_TO_ACCESS_DATADIR.getValue());
} catch (AdminServerException e) {
LOG.error("Unable to start AdminServer, exiting abnormally", e);
System.err.println("Unable to start AdminServer, exiting abnormally");
ZKAuditProvider.addServerStartFailureAuditLog();
ServiceUtils.requestSystemExit(ExitCode.ERROR_STARTING_ADMIN_SERVER.getValue());
} catch (Exception e) {
LOG.error("Unexpected exception, exiting abnormally", e);
ZKAuditProvider.addServerStartFailureAuditLog();
ServiceUtils.requestSystemExit(ExitCode.UNEXPECTED_ERROR.getValue());
}
LOG.info("Exiting normally");
ServiceUtils.requestSystemExit(ExitCode.EXECUTION_FINISHED.getValue());
}
这个方法和QuorumPeerMain的main方法差不多。
进入ZooKeeperServerMain的initializeAndRun成员方法
protected void initializeAndRun(String[] args) throws ConfigException, IOException, AdminServerException {
try {
ManagedUtil.registerLog4jMBeans();
} catch (JMException e) {
LOG.warn("Unable to register log4j JMX control", e);
}
ServerConfig config = new ServerConfig();
if (args.length == 1) {
config.parse(args[0]);
} else {
config.parse(args);
}
runFromConfig(config);
}
主要包含以下步骤：
- 从命令行参数或者配置文件中加载配置。
- 将配置传给runFromConfig成员方法，并调用该方法。
进入ZooKeeperServerMain的runFromConfig成员方法
public void runFromConfig(ServerConfig config) throws IOException, AdminServerException {
LOG.info("Starting server");
FileTxnSnapLog txnLog = null;
try {
try {
metricsProvider = MetricsProviderBootstrap.startMetricsProvider(
config.getMetricsProviderClassName(),
config.getMetricsProviderConfiguration());
} catch (MetricsProviderLifeCycleException error) {
throw new IOException("Cannot boot MetricsProvider " + config.getMetricsProviderClassName(), error);
}
ServerMetrics.metricsProviderInitialized(metricsProvider);
// Note that this thread isn't going to be doing anything else,
// so rather than spawning another thread, we will just call
// run() in this thread.
// create a file logger url from the command line args
txnLog = new FileTxnSnapLog(config.dataLogDir, config.dataDir);
JvmPauseMonitor jvmPauseMonitor = null;
if (config.jvmPauseMonitorToRun) {
jvmPauseMonitor = new JvmPauseMonitor(config);
}
final ZooKeeperServer zkServer = new ZooKeeperServer(jvmPauseMonitor, txnLog, config.tickTime, config.minSessionTimeout, config.maxSessionTimeout, config.listenBacklog, null, config.initialConfig);
txnLog.setServerStats(zkServer.serverStats());
// Registers shutdown handler which will be used to know the
// server error or shutdown state changes.
final CountDownLatch shutdownLatch = new CountDownLatch(1);
zkServer.registerServerShutdownHandler(new ZooKeeperServerShutdownHandler(shutdownLatch));
// Start Admin server
adminServer = AdminServerFactory.createAdminServer();
adminServer.setZooKeeperServer(zkServer);
adminServer.start();
boolean needStartZKServer = true;
if (config.getClientPortAddress() != null) {
cnxnFactory = ServerCnxnFactory.createFactory();
cnxnFactory.configure(config.getClientPortAddress(), config.getMaxClientCnxns(), config.getClientPortListenBacklog(), false);
cnxnFactory.startup(zkServer);
// zkServer has been started. So we don't need to start it again in secureCnxnFactory.
needStartZKServer = false;
}
if (config.getSecureClientPortAddress() != null) {
secureCnxnFactory = ServerCnxnFactory.createFactory();
secureCnxnFactory.configure(config.getSecureClientPortAddress(), config.getMaxClientCnxns(), config.getClientPortListenBacklog(), true);
secureCnxnFactory.startup(zkServer, needStartZKServer);
}
containerManager = new ContainerManager(
zkServer.getZKDatabase(),
zkServer.firstProcessor,
Integer.getInteger("znode.container.checkIntervalMs", (int) TimeUnit.MINUTES.toMillis(1)),
Integer.getInteger("znode.container.maxPerMinute", 10000),
Long.getLong("znode.container.maxNeverUsedIntervalMs", 0)
);
containerManager.start();
ZKAuditProvider.addZKStartStopAuditLog();
// Watch status of ZooKeeper server. It will do a graceful shutdown
// if the server is not running or hits an internal error.
shutdownLatch.await();
shutdown();
if (cnxnFactory != null) {
cnxnFactory.join();
}
if (secureCnxnFactory != null) {
secureCnxnFactory.join();
}
if (zkServer.canShutdown()) {
zkServer.shutdown(true);
}
} catch (InterruptedException e) {
// warn, but generally this is ok
LOG.warn("Server interrupted", e);
} finally {
if (txnLog != null) {
txnLog.close();
}
if (metricsProvider != null) {
try {
metricsProvider.stop();
} catch (Throwable error) {
LOG.warn("Error while stopping metrics", error);
}
}
}
}
主要包含以下步骤：
- 根据配置初始化监控指标收集类，并开始收集指标信息。
- 初始化事务日志和快照日志。
- 初始化JVM暂停监控器。
- 初始化ZookeeperServer，注册相关钩子。
- 初始化AdminServer并启动。
- 启动ZookeeperServer。ServerCnxnFactory负责接受客户端请求，并调用ZookeeperServer的方法将请求传给ZookeeperServer处理。
- 初始化ContainerManager并启动。ContainerManager负责清理没有子节点的container节点(zk的一种节点类型)。