jedis-sentinel原理分析

原理

客户端通过连接到哨兵集群，通过发送Protocol.SENTINEL_GET_MASTER_ADDR_BY_NAME 命令，从哨兵机器中

询问master节点的信息，拿到master节点的ip和端口号以后，再到客户端发起连接。连接以后，需要在客户端建

立监听机制，当master重新选举之后，客户端需要重新连接到新的master节点

private HostAndPort initSentinels(Set<String> sentinels, final String masterName) {
HostAndPort master = null;
boolean sentinelAvailable = false;
log.info("Trying to find master from available Sentinels...");
// 有多个sentinels,遍历这些个sentinels
for (String sentinel : sentinels) {
// host:port表示的sentinel地址转化为一个HostAndPort对象。
final HostAndPort hap = HostAndPort.parseString(sentinel);
log.fine("Connecting to Sentinel " + hap);
Jedis jedis = null;
try {
// 连接到sentinel
jedis = new Jedis(hap.getHost(), hap.getPort());
// 根据masterName得到master的地址，返回一个list，host= list[0], port =// list[1]
List<String> masterAddr = jedis.sentinelGetMasterAddrByName(masterName);
// connected to sentinel...
sentinelAvailable = true;if (masterAddr == null || masterAddr.size() != 2) {
log.warning("Can not get master addr, master name: " + masterName + ".
Sentinel: " + hap
+ ".");
continue;
}
// 如果在任何一个sentinel中找到了master，不再遍历sentinels
master = toHostAndPort(masterAddr);
log.fine("Found Redis master at " + master);
break;
} catch (JedisException e) {
// resolves #1036, it should handle JedisException there's another chance
// of raising JedisDataException
log.warning("Cannot get master address from sentinel running @ " + hap + ".
Reason: " + e
+ ". Trying next one.");
} finally {
if (jedis != null) {
jedis.close();
}
}
}
// 到这里，如果master为null，则说明有两种情况，一种是所有的sentinels节点都down掉了，一种是master节
点没有被存活的sentinels监控到
if (master == null) {
if (sentinelAvailable) {
// can connect to sentinel, but master name seems to not
// monitored
throw new JedisException("Can connect to sentinel, but " + masterName
+ " seems to be not monitored...");
} else {
throw new JedisConnectionException("All sentinels down, cannot determine where is
"
+ masterName + " master is running...");
}
}
//如果走到这里，说明找到了master的地址
log.info("Redis master running at " + master + ", starting Sentinel listeners...");
//启动对每个sentinels的监听
//为每个sentinel都启动了一个监听者MasterListener。MasterListener本身是一个线程，它会去订阅sentinel
上关于master节点地址改变的消息。
for (String sentinel : sentinels) {
final HostAndPort hap = HostAndPort.parseString(sentinel);
MasterListener masterListener = new MasterListener(masterName, hap.getHost(),
hap.getPort());
// whether MasterListener threads are alive or not, process can be stopped
masterListener.setDaemon(true);
masterListeners.add(masterListener);
masterListener.start();
}
return master;
}
从哨兵节点获取master信息的方法

public List<String> sentinelGetMasterAddrByName(String masterName) {

client.sentinel(Protocol.SENTINEL_GET_MASTER_ADDR_BY_NAME, masterName);

final List<Object> reply = client.getObjectMultiBulkReply();

return BuilderFactory.STRING_LIST.build(reply);

}