Redis (15) -- master-slave replication of redis -- sentinel mode

11.5） Sentinel mode

11.5.1） brief introduction

The automatic version of anti guest oriented , Be able to monitor the failure of the host in the background , If it fails, it will automatically convert from the library to the main library according to the number of votes

11.5.2） Use steps

11.5.2.1） Adjust to one master and two servants mode

127.0.0.1:11079> info replication
# Replication
role:master
connected_slaves:2
slave0:ip=127.0.0.1,port=11081,state=online,offset=266,lag=1
slave1:ip=127.0.0.1,port=11080,state=online,offset=266,lag=1
master_failover_state:no-failover
master_replid:e504980f294d5cb1c873bf68464b81ce21294369
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:266
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:1
repl_backlog_histlen:266

11079 ： host

11080 、11081： Slave

11.5.2.2） New configuration file

Self defined /myredis New under the directory sentinel.conf file

sentinel monitor mymaster 127.0.0.1 11079 1

Execute startup command ：

redis-sentinel  /root/myredis/sentinel.conf

Successful launch ：

[root@VM-20-6-centos bin]# redis-sentinel  /root/myredis/sentinel.conf
17788:X 21 Apr 2022 00:31:15.637 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
17788:X 21 Apr 2022 00:31:15.637 # Redis version=6.2.6, bits=64, commit=00000000, modified=0, pid=17788, just started
17788:X 21 Apr 2022 00:31:15.637 # Configuration loaded
17788:X 21 Apr 2022 00:31:15.638 * monotonic clock: POSIX clock_gettime
                _._                                                  
           _.-``__ ''-._                                             
      _.-``    `.  `_.  ''-._           Redis 6.2.6 (00000000/0) 64 bit
  .-`` .-```.  ```\/    _.,_ ''-._                                  
 (    '      ,       .-`  | `,    )     Running in sentinel mode
 |`-._`-...-` __...-.``-._|'` _.-'|     Port: 26379
 |    `-._   `._    /     _.-'    |     PID: 17788
  `-._    `-._  `-./  _.-'    _.-'                                   
 |`-._`-._    `-.__.-'    _.-'_.-'|                                  
 |    `-._`-._        _.-'_.-'    |           https://redis.io       
  `-._    `-._`-.__.-'_.-'    _.-'                                   
 |`-._`-._    `-.__.-'    _.-'_.-'|                                  
 |    `-._`-._        _.-'_.-'    |                                  
  `-._    `-._`-.__.-'_.-'    _.-'                                   
      `-._    `-.__.-'    _.-'                                       
          `-._        _.-'                                           
              `-.__.-'                                               
​
17788:X 21 Apr 2022 00:31:15.639 # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of 128.
17788:X 21 Apr 2022 00:31:15.647 # Sentinel ID is cb52f79e99489e385a57361aef7982875b0384aa
17788:X 21 Apr 2022 00:31:15.647 # +monitor master mymaster 127.0.0.1 11079 quorum 1
17788:X 21 Apr 2022 00:31:15.648 * +slave slave 127.0.0.1:11081 127.0.0.1 11081 @ mymaster 127.0.0.1 11079
17788:X 21 Apr 2022 00:31:15.655 * +slave slave 127.0.0.1:11080 127.0.0.1 11080 @ mymaster 127.0.0.1 11079

11.5.2.3） test

Stop the host service ：

127.0.0.1:11079> shutdown
not connected> exit

Above redis-sentinel Interface ：

17788:X 21 Apr 2022 00:34:33.399 # +promoted-slave slave 127.0.0.1:11080 127.0.0.1 11080 @ mymaster 127.0.0.1 11079
17788:X 21 Apr 2022 00:34:33.399 # +failover-state-reconf-slaves master mymaster 127.0.0.1 11079
17788:X 21 Apr 2022 00:34:33.482 * +slave-reconf-sent slave 127.0.0.1:11081 127.0.0.1 11081 @ mymaster 127.0.0.1 11079
17788:X 21 Apr 2022 00:34:34.438 * +slave-reconf-inprog slave 127.0.0.1:11081 127.0.0.1 11081 @ mymaster 127.0.0.1 11079
17788:X 21 Apr 2022 00:34:34.438 * +slave-reconf-done slave 127.0.0.1:11081 127.0.0.1 11081 @ mymaster 127.0.0.1 11079
17788:X 21 Apr 2022 00:34:34.509 # +failover-end master mymaster 127.0.0.1 11079
17788:X 21 Apr 2022 00:34:34.509 # +switch-master mymaster 127.0.0.1 11079 127.0.0.1 11080
17788:X 21 Apr 2022 00:34:34.509 * +slave slave 127.0.0.1:11081 127.0.0.1 11081 @ mymaster 127.0.0.1 11080
17788:X 21 Apr 2022 00:34:34.509 * +slave slave 127.0.0.1:11079 127.0.0.1 11079 @ mymaster 127.0.0.1 11080

It can be seen that the slave 11080 Switch to host , Restart the host , see 11079 Service information ：

127.0.0.1:11079> info replication
# Replication
role:slave
master_host:127.0.0.1
master_port:11080
master_link_status:up
master_last_io_seconds_ago:1

see 11080 Service information ：

127.0.0.1:11080> info replication
# Replication
role:master
connected_slaves:2
slave0:ip=127.0.0.1,port=11081,state=online,offset=32883,lag=0
slave1:ip=127.0.0.1,port=11079,state=online,offset=32869,lag=0
master_failover_state:no-failover
master_replid:e2db42e820ac3d927269cd59ef3bc775e7e5405f
master_replid2:e504980f294d5cb1c873bf68464b81ce21294369
master_repl_offset:32883
second_repl_offset:12586
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:225
repl_backlog_histlen:32659

It is found that the above has automatically removed the host from 11079 Switch to a 11080 了

11.5.3） Replication delay

Because all write operations are performed on the host first (Master) On the operation , Then synchronize the update to the slave (Slave) On , So from the host (Master) Synchronize to slave (Slave) There is a certain delay , When the system is busy , The delay problem will be more serious , Slave (Slave) The increase in the number of machines will make the problem more serious .

11.5.4） Fault recovery （ Election rules ）

1、 The priority is redis.conf The default , The lower the value, the higher the priority ;

 

replica-priority 100

 

2、 Offset ： It refers to the one that obtains the most complete data of the original host ;

3、 Every redis After the instance is started, it will generate one randomly 40 Bit runid;

11.5.5）Jedis Implement sentinel mode

    private static JedisSentinelPool jedisSentinelPool = null;
​
    public static Jedis getJedisFromSentinel() {
        if (jedisSentinelPool == null) {
            Set<String> sentinelSet = new HashSet<>();
            sentinelSet.add("127.0.0.1:26379");
            JedisPoolConfig jedisPoolConfig = new JedisPoolConfig();
            jedisPoolConfig.setMaxTotal(10); // Maximum number of connections available 
            jedisPoolConfig.setMaxIdle(5); // Maximum number of idle connections 
            jedisPoolConfig.setMinIdle(5); // Minimum number of idle connections 
            jedisPoolConfig.setBlockWhenExhausted(true); // Whether the connection is exhausted and wait 
            jedisPoolConfig.setMaxWaitMillis(2000); // Waiting time 
            jedisPoolConfig.setTestOnBorrow(true); // Test the connection  ping pong
            jedisSentinelPool = new JedisSentinelPool("mymaster", sentinelSet, jedisPoolConfig);
            return jedisSentinelPool.getResource();
        } else {
            return jedisSentinelPool.getResource();
        }
    }