这个时候如果sentinel没有设置后台运行，可以在命令行窗口看到 master切换的情况日志。
# Sentinel ID is fd0634dc9876ec60da65db5ff1e50ebbeefdf5ce # +monitor master mymaster 127.0.0.1 63791 quorum 1 * +slave slave 127.0.0.1:63792 127.0.0.1 63792 @ mymaster 127.0.0.1 63791 * +slave slave 127.0.0.1:63793 127.0.0.1 63793 @ mymaster 127.0.0.1 63791 # +sdown master mymaster 127.0.0.1 63791 # +odown master mymaster 127.0.0.1 63791 #quorum 1/1 # +new-epoch 1 # +try-failover master mymaster 127.0.0.1 63791 # +vote-for-leader fd0634dc9876ec60da65db5ff1e50ebbeefdf5ce 1 # +elected-leader master mymaster 127.0.0.1 63791 # +failover-state-select-slave master mymaster 127.0.0.1 63791 # +selected-slave slave 127.0.0.1:63793 127.0.0.1 63793 @ mymaster 127.0.0.1 63791 * +failover-state-send-slaveof-noone slave 127.0.0.1:63793 127.0.0.1 63793 @ mymaster 127.0.0.1 63791 * +failover-state-wait-promotion slave 127.0.0.1:63793 127.0.0.1 63793 @ mymaster 127.0.0.1 63791 # +promoted-slave slave 127.0.0.1:63793 127.0.0.1 63793 @ mymaster 127.0.0.1 63791 # +failover-state-reconf-slaves master mymaster 127.0.0.1 63791 * +slave-reconf-sent slave 127.0.0.1:63792 127.0.0.1 63792 @ mymaster 127.0.0.1 63791 * +slave-reconf-inprog slave 127.0.0.1:63792 127.0.0.1 63792 @ mymaster 127.0.0.1 63791 * +slave-reconf-done slave 127.0.0.1:63792 127.0.0.1 63792 @ mymaster 127.0.0.1 63791 # +failover-end master mymaster 127.0.0.1 63791 # +switch-master mymaster 127.0.0.1 63791 127.0.0.1 63793 * +slave slave 127.0.0.1:63792 127.0.0.1 63792 @ mymaster 127.0.0.1 63793 * +slave slave 127.0.0.1:63791 127.0.0.1 63791 @ mymaster 127.0.0.1 63793 # +sdown slave 127.0.0.1:63791 127.0.0.1 63791 @ mymaster 127.0.0.1 63793 # -sdown slave 127.0.0.1:63791 127.0.0.1 63791 @ mymaster 127.0.0.1 63793 * +convert-to-slave slave 127.0.0.1:63791 127.0.0.1 63791 @ mymaster 127.0.0.1 63793上面的日志较多，仔细找找可以看到下面几行主要的：
初始情况下，1主2从 # +monitor master mymaster 127.0.0.1 63791 quorum 1 * +slave slave 127.0.0.1:63792 127.0.0.1 63792 @ mymaster 127.0.0.1 63791 * +slave slave 127.0.0.1:63793 127.0.0.1 63793 @ mymaster 127.0.0.1 63791 发现主挂了，准备 故障转移 # +try-failover master mymaster 127.0.0.1 63791 将主切换到了 63793 即redis03 # +switch-master mymaster 127.0.0.1 63791 127.0.0.1 63793这个日志比较晦涩，从代码运行效果看，如下：
14:45:20.675 [main] INFO redis.clients.jedis.JedisSentinelPool - Trying to find master from available Sentinels... 14:45:25.731 [main] DEBUG redis.clients.jedis.JedisSentinelPool - Connecting to Sentinel 192.168.1.106:26379 14:45:25.770 [main] DEBUG redis.clients.jedis.JedisSentinelPool - Found Redis master at 127.0.0.1:63792 14:45:25.771 [main] INFO redis.clients.jedis.JedisSentinelPool - Redis master running at 127.0.0.1:63792, starting Sentinel listeners... 14:45:25.871 [main] INFO redis.clients.jedis.JedisSentinelPool - Created JedisPool to master at 127.0.0.1:63792 ejahaeegig-->true deeeadejjf-->true [ exception happened]redis.clients.jedis.exceptions.JedisConnectionException: Could not get a resource from the pool [ exception happened]........ [ exception happened]........ [ exception happened]........ [ exception happened]........ [ exception happened]........ [ exception happened]........ [ exception happened]........ [ exception happened]........ [ exception happened]........ 14:46:02.737 [MasterListener-mymaster-[192.168.1.106:26379]] DEBUG redis.clients.jedis.JedisSentinelPool - Sentinel 192.168.1.106:26379 published: mymaster 127.0.0.1 63792 127.0.0.1 63793. 14:46:02.738 [MasterListener-mymaster-[192.168.1.106:26379]] INFO redis.clients.jedis.JedisSentinelPool - Created JedisPool to master at 127.0.0.1:63793 haiihiihbb-->true ifgebdcicd-->true aajhbjagag-->true Process finished with exit code 0从结果看出
开始正常操作redis，并设置了两次。
主redis挂了，jedis得不到连接，报错了JedisConnectionException：Could not get a resource from the pool
主redis没选好之前，程序持续报错。
主redis选好了，程序正常运行，最后结束。
我们看到最后一次运行设置的值是aajhbjagag,我们可以连接剩下的2台redis中的任意一台，get hello,结果肯定是一致的。
redis cluster上面的章节中，我们分别学习了redis 单点，redis主从，并增加了高可用的 sentinel 哨兵模式。我们所做的这些工作只是保证了数据备份以及高可用，目前为止我们的程序一直都是向1台redis写数据，其他的redis只是备份而已。实际场景中，单个redis节点可能不满足要求，因为：
单个redis并发有限
单个redis接收所有的数据，最终回导致内存太大，内存太大回导致rdb文件过大，从很大的rdb文件中同步恢复数据会很慢。
所有，我们需要redis cluster 即redis集群。
Redis 集群是一个提供在多个Redis间节点间共享数据的程序集。