Redis Sentinel高可用集群Java客户端

java客户端Jedis在2.2.2及以上版本实现了对Sentinel的支持，只要是通过命令：
redis-cli -h 192.168.110.71 -p 6000  sentinel get-master-addr-by-name shard_a
1) "192.168.110.71"
2) "6379"
查询分片shard_a的主服务器地址，实现代码如下：

private HostAndPort initSentinels(Set<String> sentinels, final String masterName) {    HostAndPort master = null;    boolean sentinelAvailable = false;    log.info("Trying to find master from available Sentinels...");    for (String sentinel : sentinels) {      final HostAndPort hap = toHostAndPort(Arrays.asList(sentinel.split(":")));      log.fine("Connecting to Sentinel " + hap);      Jedis jedis = null;      try {        jedis = new Jedis(hap.getHost(), hap.getPort());        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;        }        master = toHostAndPort(masterAddr);        log.fine("Found Redis master at " + master);        break;      } catch (JedisConnectionException e) {        log.warning("Cannot connect to sentinel running @ " + hap + ". Trying next one.");      } finally {        if (jedis != null) {          jedis.close();        }      }    }    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...");      }    }    log.info("Redis master running at " + master + ", starting Sentinel listeners...");    for (String sentinel : sentinels) {      final HostAndPort hap = toHostAndPort(Arrays.asList(sentinel.split(":")));      MasterListener masterListener = new MasterListener(masterName, hap.getHost(), hap.getPort());      masterListeners.add(masterListener);      masterListener.start();    }    return master;  }

关于在java应用中如何使用，请参考如下代码实例：

package cn.slimsmart.redis.demo.sentinel;import java.util.HashSet;import java.util.Set;import redis.clients.jedis.Jedis;import redis.clients.jedis.JedisSentinelPool;public class JedisSentinelTest {public static void main(String[] args) {Set<String> sentinels = new HashSet<String>();sentinels.add("192.168.100.90:6000");sentinels.add("192.168.110.71:6000");/** * masterName 分片的名称 * sentinels Redis Sentinel 服务地址列表 */JedisSentinelPool poolA = new JedisSentinelPool("shard_a", sentinels);JedisSentinelPool poolB = new JedisSentinelPool("shard_b", sentinels);//获取Jedis主服务器客户端实例Jedis jedisA = poolA.getResource();jedisA.set("key", "abc");Jedis jedisB = poolB.getResource();jedisB.set("key", "xyz");System.out.println("jedisA key:"+jedisA.get("key"));System.out.println("jedisB key:"+jedisB.get("key"));//输出结果//jedisA key:abc//jedisB key:xyz}}

由上面代码可以看出jedis的JedisSentinelPool需要指定分片名称即主服务名称（masterName），这样根据需求硬编码将缓存数据添加到对应的分片中，无法自动分片。若使用ShardedJedisPool，当分片发生主从切换无法获得通知，所有对那个分片的操作将会失败。下面我们介绍一个开源项目sharded-jedis-sentinel-pool，能及时感知所有分片主从切换行为，进行连接池重建。
项目源码：https://github.com/warmbreeze/sharded-jedis-sentinel-pool
一、ShardedJedisSentinelPool实现分析
1.构造函数
public ShardedJedisSentinelPool(final GenericObjectPoolConfig poolConfig, List<String> masters, Set<String> sentinels) 
类似之前的Jedis Pool的构造方法，需要参数poolConfig提供诸如maxIdle，maxTotal之类的配置，masters是一个List，用来保存所有分片Master在Sentinel中配置的名字（注意master的顺序不能改变，因为Shard算法是依据分片位置进行计算，如果顺序错误将导致数据存储混乱），sentinels是一个Set，其中存放所有Sentinel的地址(格式：IP:PORT，如127.0.0.1:26379)，顺序无关；
2.初始化连接池
在构造函数中，通过方法
private List<HostAndPort> initSentinels(Set<String> sentinels, final List<String> masters) 
取得当前所有分片的master地址(IP&PORT)，对每个分片，通过顺次连接Sentinel实例，获取该分片的master地址，如果无法获得，即所有Sentinel都无法连接，将休眠1秒后继续重试，直到取得所有分片的master地址，代码块如下： 

for (String masterName : masters) {HostAndPort master = null;boolean fetched = false;while (!fetched && sentinelRetry < MAX_RETRY_SENTINEL) {for (String sentinel : sentinels) {final HostAndPort hap = toHostAndPort(Arrays.asList(sentinel.split(":")));log.fine("Connecting to Sentinel " + hap);try {Jedis jedis = new Jedis(hap.getHost(), hap.getPort());master = masterMap.get(masterName);if (master == null) {List<String> hostAndPort = jedis.sentinelGetMasterAddrByName(masterName);if (hostAndPort != null && hostAndPort.size() > 0) {master = toHostAndPort(hostAndPort);log.fine("Found Redis master at " + master);shardMasters.add(master);masterMap.put(masterName, master);fetched = true;jedis.disconnect();break;}}} catch (JedisConnectionException e) {log.warning("Cannot connect to sentinel running @ " + hap + ". Trying next one.");}}if (null == master) {try {log.severe("All sentinels down, cannot determine where is " + masterName + " master is running... sleeping 1000ms, Will try again.");Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}fetched = false;sentinelRetry++;}}// Try MAX_RETRY_SENTINEL times.if (!fetched && sentinelRetry >= MAX_RETRY_SENTINEL) {log.severe("All sentinels down and try " + MAX_RETRY_SENTINEL + " times, Abort.");throw new JedisConnectionException("Cannot connect all sentinels, Abort.");}}

通过private void initPool(List<HostAndPort> masters)初始化连接池，到此连接池中的所有连接都指向分片的master。

3.监控每个Sentinel
在方法
public ShardedJedisSentinelPool(final GenericObjectPoolConfig poolConfig, List<String> masters, Set<String> sentinels)
最后，会为每个Sentinel启动一个Thread来监控Sentinel做出的更改： 
protected class MasterListener extends Thread
该线程的run方法通过Jedis Pub/Sub API（实现JedisPubSub接口，并通过jedis.subscribe进行订阅）向Sentinel实例订阅“+switch-master”频道，当Sentinel进行主从切换时，该线程会得到新Master地址的通知，通过master name判断哪个分片进行了切换，将新master地址替换原来位置的地址，并调用initPool(List masters)进行Jedis连接池重建；后续所有通过该连接池取得的连接都指向新Master地址，对应用程序透明。

二、应用实例

package cn.slimsmart.redis.demo.sentinel;import java.util.ArrayList;import java.util.HashSet;import java.util.List;import java.util.Set;import org.apache.commons.pool2.impl.GenericObjectPoolConfig;import redis.clients.jedis.ShardedJedis;public class ShardedJedisSentinelTest {public static void main(String[] args) {//连接池配置GenericObjectPoolConfig poolConfig = new GenericObjectPoolConfig();//分片配置List<String> masters = new ArrayList<String>();masters.add("shard_a");masters.add("shard_b");//sentinel服务节点Set<String> sentinels = new HashSet<String>();sentinels.add("192.168.100.90:6000");sentinels.add("192.168.110.71:6000");//创建分片连接池ShardedJedisSentinelPool pool = new ShardedJedisSentinelPool(poolConfig, masters, sentinels);ShardedJedis jedis = null;try {jedis = pool.getResource();jedis.set("key_sharded", "abc");System.out.println(jedis.get("key_sharded"));} finally {if (jedis != null){pool.returnResource(jedis);}pool.destroy();}}}

运行后，通过redis客户端查看：

redis 192.168.110.71:6379> get key_sharded
"abc"

redis 192.168.110.71:6380> get key_sharded
(nil)

可以看出key_sharded被添加到shard_a分片中。
集成spring配置参考：

<?xml version="1.0" encoding="UTF-8"?><beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"xmlns:tx="http://www.springframework.org/schema/tx" xmlns:aop="http://www.springframework.org/schema/aop"xmlns:context="http://www.springframework.org/schema/context"xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.0.xsdhttp://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd"default-lazy-init="false" default-autowire="byName"><bean id="shardedJedisPool" class="cn.slimsmart.redis.demo.sentinel.ShardedJedisSentinelPool"><constructor-arg index="0" ref="jedisPoolConfig" /><constructor-arg index="1"><list><value>shard_a</value><value>shard_b</value></list></constructor-arg><constructor-arg index="2"><set><value>192.168.100.90:6000</value><value>192.168.110.71:6000</value></set></constructor-arg></bean><bean id="jedisPoolConfig" class="redis.clients.jedis.JedisPoolConfig"><property name="maxTotal" value="200" /><property name="maxIdle" value="100" /><property name="maxWaitMillis" value="5000" /><property name="testOnBorrow" value="true" /></bean></beans>

参考文章：

1.基于Redis Sentinel的Redis集群(主从&Sharding)高可用方案

2.Redis主从复制和主从切换(spring 集成)