Redis Sentinel Deployment Process

Keywords: Programming Redis Jedis Java CentOS

Edition

CentOS 8.1.1911(VMWare)
redis 5.0.8

Essential information

Server IP: 192.168.31.68
 Redis port: 7000 (primary) 7001,7002 (slave)
Sentinel port: 27000 27001 27002

The key code or command represents this

Configure Redis

master7000.conf

bind 0.0.0.0
port 7000
daemonize yes
dir /home/misty/redis-data/sentinel01
pidfile /var/run/redis_7000.pid
logfile "7000.log"
dbfilename dump7000.rdb

slave7001.conf

bind 0.0.0.0
port 7001
daemonize yes
dir /home/misty/redis-data/sentinel01
pidfile /var/run/redis_7001.pid
logfile "7001.log"
dbfilename dump7001.rdb
slaveof 192.168.31.68 7000

slave7002.conf

bind 0.0.0.0
port 7002
daemonize yes
dir /home/misty/redis-data/sentinel01
pidfile /var/run/redis_7002.pid
logfile "7002.log"
dbfilename dump7002.rdb
slaveof 192.168.31.68 7000

Start Redis Service

Start redis

redis-server master7000.conf
redis-server slave7001.conf
redis-server slave7002.conf

Validation service started

$ ps -ef | grep redis-server | grep -v grep
misty      4633   2639  0 03:16 ?        00:00:00 redis-server 0.0.0.0:7000
misty      4649   2639  0 03:16 ?        00:00:00 redis-server 0.0.0.0:7001
misty      4663   2639  0 03:16 ?        00:00:00 redis-server 0.0.0.0:7002

Redis automatically establishes a master-slave relationship

redis:7000> info replication
# Replication
role:master
connected_slaves:2
slave0:ip=192.168.31.68,port=7001,state=online,offset=630,lag=0
slave1:ip=192.168.31.68,port=7002,state=online,offset=630,lag=1
master_replid:187ff0474ccd0303571db1ca94174c46c2476dba
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:630

The master knows two slave node information.Notable is offset, where the master and slave nodes determine whether they are synchronized or not.

redis:7001> info replication
# Replication
role:slave
master_host:192.168.31.68
master_port:7000
master_link_status:up
master_last_io_seconds_ago:6
master_sync_in_progress:0
slave_repl_offset:882
slave_priority:100
slave_read_only:1
connected_slaves:0
master_replid:187ff0474ccd0303571db1ca94174c46c2476dba
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:882

Note here that slave_priority, in sentinel mode, if master is down, sentinel first decides who to promote to master based on slave_priority.

By default, slave_priority is the same for all nodes, so the largest choice is based on offset.

If no successor can be selected, choose master with the smallest runID (oldest seniority).

The runID is viewed through info server.

At this point we think shutdown drops the master node, and the slave node shows that the master node is down.The slave node is not automatically promoted to master.

# Replication
role:slave
master_host:192.168.31.68
master_port:7000
master_link_status:down
master_last_io_seconds_ago:-1

Restart master node and restore state to up

Configure Sentinel

sentinel27000.conf

port 27000
daemonize yes
pidfile /var/run/redis-sentinel.pid
logfile "sentinel27000.log"
dir /home/misty/redis-data/sentinel01
sentinel monitor mymaster 192.168.31.68 7000 2
sentinel down-after-milliseconds mymaster 30000
sentinel parallel-syncs mymaster 1
sentinel failover-timeout mymaster 180000
sentinel deny-scripts-reconfig yes

Since the profiles only have different port numbers, only one profile is posted.Can be created in batches with the sed command

sentinel27001.conf

sed "s/27000/27001/g" sentinel27000.conf > sentinel27001.conf

We will note that sentinel's configuration information does not identify the presence of other sentinels, only the master node's information.When sentinel service is started, the presence of other sentinel and slave nodes is automatically perceived through the master node between sentinel nodes.

sentinel will modify the configuration file after it is started. It is recommended that you back up the configuration file.

Start sentinel

redis-sentinel sentinel27000.conf
redis-sentinel sentinel27001.conf
redis-sentinel sentinel27002.conf

Verify sentinel started successfully:

> ps -ef | grep redis-sentinel | grep -v grep
misty      5516   2639  0 03:59 ?        00:00:00 redis-sentinel *:27000 [sentinel]
misty      5528   2639  0 04:00 ?        00:00:00 redis-sentinel *:27001 [sentinel]
misty      5539   2639  0 04:00 ?        00:00:00 redis-sentinel *:27002 [sentinel]

Connect to any sentinel using redis-cli and run info sentinel to get the same information

# Sentinel
sentinel_masters:1
sentinel_tilt:0
sentinel_running_scripts:0
sentinel_scripts_queue_length:0
sentinel_simulate_failure_flags:0
master0:name=mymaster,status=ok,address=192.168.31.68:7000,slaves=2,sentinels=3

A sentinel group can manage multiple redis master-slave groups, distinguished by master:name

Test Master-Slave Switching

We shutdown down the 7000 nodes and wait a moment to see that the primary node has switched to 7001.

sentinel:27000> info sentinel
...
master0:name=mymaster,status=ok,address=192.168.31.68:7001,slaves=2,sentinels=3

Show that there are still two slaves, when looking at the 7001 node, we found that there is only one slave with 7002 left

redis:7001> info replication
# Replication
...
slave0:ip=192.168.31.68,port=7002,state=online,offset=227471,lag=0

When the redis:7000 service is restarted, it is automatically set to slave redis:7001

redis:7001> info replication
# Replication
...
slave0:ip=192.168.31.68,port=7002,state=online,offset=299880,lag=0
slave1:ip=192.168.31.68,port=7000,state=online,offset=299880,lag=1

complete

At this point, a basic EDIS Sentinel group has been set up.

The redis sentinel node is only responsible for monitoring, not for the forwarding of commands such as add-delete checks, and the client still needs to connect to the actual Redis master node for operation.(different from Cluster)

Appendix: Java Connection Redis Sentinel

import org.apache.commons.pool2.impl.GenericObjectPoolConfig;
import redis.clients.jedis.JedisSentinelPool;

import java.util.HashSet;

public class Sentinel {
  public static void main(String[] args) {
    var poolConfig = new GenericObjectPoolConfig<>();
    poolConfig.setMaxTotal(10);
    var sentinels = new HashSet<String>();
    sentinels.add("192.168.31.68:27000");
    sentinels.add("192.168.31.68:27001");
    sentinels.add("192.168.31.68:27002");

    var sentinelPool = new JedisSentinelPool("mymaster", sentinels, poolConfig, 30000);
    try (var jedis = sentinelPool.getResource()) {
      jedis.set("hello", "world");
      System.out.println(jedis.get("hello"));
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}

If Redis is unable to connect, modify the server firewall to open related ports

Client Principles

Select an available Sentinel node
Visit sentinel to get master information: sentinel get-master-addr-by-name mymaster
Verify master node:role
Create connection pool
Listen for sentinel and rebuild connection pool after master node changes

Posted by DJP1986 on Sun, 19 Apr 2020 03:20:08 -0700

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