Redis master-slave replication

One 、Redis Master slave replication overview

（1） Master slave replication overview

• In order to share the Redis The pressure of reading and writing ,Redis Support master-slave replication ,Redis The master-slave structure of can adopt one master-slave or cascade structure
• Redis The synchronization types of master-slave replication are divided into full synchronization and incremental synchronization

Full amount of synchronization

Redis The full synchronization of generally occurs in Slave Server initialization phase , That is, just joined the cluster or Slave After downtime and restart , This is the time Slave Need to put Master Synchronize all data on , The following is the process of synchronization ：（ The command of synchronization is write command ）

1. **Slave Server connection Master The server , send out SYNC（ Sync ） command ,Slave The first time the server sends Master When the server synchronizes , It won't affect Master The server receives the request from the client **
2. Master The server receives Slave Server's SYNC After the command , Start execution bgsave Command to take a database snapshot to generate RDB File and use a buffer to record all commands executed since , in other words Master Will take a snapshot of the current database , Then it will put all the subsequent commands into its own cache
3. Master Server bgsave After command execution , To all Slave Server send RDB file , And continue to record the executed commands to its own cache during sending
4. Slave The server is receiving Master Server's RDB After the document , You will lose all your data , Then load RDB file , In fact, at this time Slave The full backup has been completed , But because RDB There are also executed commands after the file , So we need to Master Commands executed after server synchronization
5. Master Server to the Slave The server sends the executed command in the cache
6. Slave The server has finished checking RDB After loading the file , Will continue to receive Master The command of the cache sent by the server is synchronized

Once the above operations are completed Slave Initialization from the server , At this time, the server can receive the read request from the user , Then synchronize Master The data of the primary server is incremental synchronization

The incremental synchronization

Redis Incremental synchronization of occurs in Slave When the server starts to work normally after the initialization phase is completed ,Master The write operation of the primary server will be synchronized to Slave Process from server

Master Every time the master server receives a write operation , Will give you Slave Send the same write operation from the server , then Slave Synchronize from the server

（2）Redis Master slave synchronization strategy

• Redis The master connected from the beginning ,Slave The slave server will perform full synchronization
• After full synchronization ,Slave The synchronization after the server is incremental
• If necessary ,Slave The server can be fully synchronized at any time
• Redis Our synchronization strategy is ： in any case ,Slave The server will first try to perform incremental synchronization , If synchronization fails , be Slave Full synchronization from the server
• Recommended Opening Master Persistence function of the master server , Because in many stations Slave When the server goes down and needs to be restarted , After restart, each Slave From the server to Master The master server sends SYNC（ Sync ） Request , and Master The server performs full synchronization , And that leads to Master Of the main server IO Rapid increase leads to Master Main server down

Two 、 To configure Redis Master-slave replication of

（1） Experimental environment

System	ip	Host name	redis edition	Play a role
Centos7.4	192.168.100.202	master	redis-5.0.4	master master server
Centos7.4	192.168.100.203	slave	redis-5.0.4	slave From the server

（2） The experiment purpose

Realization Redis Master slave copy

（3） The experimental steps

Configure two servers Redis, install Redis The two servers are the same , Different host names 、ip Different , It's just master Configuration of

[[email protected] ~]# hostnamectl set-hostname master
[[email protected] ~]# su
[[email protected] ~]# systemctl stop firewalld
[[email protected] ~]# setenforce 0
setenforce: SELinux is disabled
[[email protected] ~]# mount /dev/cdrom /mnt/
mount: /dev/sr0  Write protect , Will mount... As read-only 
mount: /dev/sr0  Already mounted or  /mnt  busy 
       /dev/sr0  It has been attached to  /mnt  On 
[[email protected] ~]# ll
 Total usage  1928
-rw-------. 1 root root    1264 1 month   12 18:27 anaconda-ks.cfg
-rw-r--r--  1 root root 1966337 6 month    9 01:16 redis-5.0.4.tar.gz
[[email protected] ~]# tar xf redis-5.0.4.tar.gz
[[email protected] ~]# cd redis-5.0.4
[[email protected] redis-5.0.4]# make
[[email protected] redis-5.0.4]# mkdir -p /usr/local/redis
[[email protected] redis-5.0.4]# cp /root/redis-5.0.4/src/redis-server /usr/local/redis/
[[email protected] redis-5.0.4]# cp /root/redis-5.0.4/src/redis-cli /usr/local/redis/
[[email protected] redis-5.0.4]# cp /root/redis-5.0.4/redis.conf /usr/local/redis/ 
[[email protected] redis-5.0.4]# vim /usr/local/redis/redis.conf # modify 
......
  68 # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  69 bind 192.168.100.202  # Change to local address , If 127.0.0.1 You can only access it locally 
  70 
......
  87 # are explicitly listed using the "bind" directive.
  88 protected-mode no  # close redis Protection mode of , If yes Other clients cannot connect to this server 
  89 
......
 135 # Note that Redis will write a pid file in /var/run/redis.pid when daemonized.
 136 daemonize yes  # Turn on redis Background daemon for , That is to say redis After it is turned on, it runs in the background 
 137 
......
 262 # Note that you must specify a directory here, not a file name.
 263 dir /usr/local/redis/rdb
 264 
......
 506 #
 507 requirepass 123123  # Remove annotations , modify redis The password for 123123
 508 
# Save and exit 
[[email protected] redis-5.0.4]# mkdir /usr/local/redis/rdb
[[email protected] redis-5.0.4]# vim /etc/init.d/redis
#!/bin/sh
# chkconfig: 2345 80 90
# description: Start and Stop redis
#PATH=/usr/local/bin:/sbin:/usr/bin:/bin
REDISPORT=6379
EXEC=/usr/local/redis/redis-server
REDIS_CLI=/usr/local/redis/redis-cli
PIDFILE=/var/run/redis_6379.pid
CONF="/usr/local/redis/redis.conf"
AUTH="123123"
LISTEN_IP=$(netstat -utpln |grep redis-server |awk '{print $4}'|awk -F':' '{print $1}')

case "$1" in
    start)
        if [ -f $PIDFILE ]
        then
                echo "$PIDFILE exists, process is already running or crashed"
        else
                echo "Starting Redis server..."
                $EXEC $CONF
        fi
        if [ "$?"="0" ]
        then
              echo "Redis is running..."
        fi
        ;;
    stop)
        if [ ! -f $PIDFILE ]
        then
                echo "$PIDFILE does not exist, process is not running"
        else
                PID=$(cat $PIDFILE)
                echo "Stopping ..."
                $REDIS_CLI -h $LISTEN_IP -p $REDISPORT -a $AUTH SHUTDOWN
                while [ -x ${PIDFILE} ]
               do
                    echo "Waiting for Redis to shutdown ..."
                    sleep 1
                done
                echo "Redis stopped"
        fi
        ;;
   restart|force-reload)
        ${0} stop
        ${0} start
        ;;
  *)
    echo "Usage: /etc/init.d/redis {start|stop|restart|force-reload}" >&2
        exit 1
esac
[[email protected] redis-5.0.4]# chkconfig --add redis
[[email protected] redis-5.0.4]# chmod 755 /etc/init.d/redis
[[email protected] redis-5.0.4]# ln -s /usr/local/redis/* /usr/local/bin/
[[email protected] redis-5.0.4]# /etc/init.d/redis start 
Starting Redis server...
5233:C 09 Jun 2021 01:25:53.069 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
5233:C 09 Jun 2021 01:25:53.069 # Redis version=5.0.4, bits=64, commit=00000000, modified=0, pid=5233, just started
5233:C 09 Jun 2021 01:25:53.069 # Configuration loaded
Redis is running...
[[email protected] redis-5.0.4]# netstat -anpt | grep 6379
tcp        0      0 192.168.100.202:6379    0.0.0.0:*               LISTEN      5234/redis-server 1 

To configure master Server master profile

[[email protected] redis-5.0.4]# vim /usr/local/redis/redis.conf # modify 
......
 456 #
 457  min-replicas-to-write 1 # Set up slave Number of servers , When slave When the number of servers is less than this ,Master The master server will stop receiving all write requests from the client 
 458  min-replicas-max-lag 10 # Set the timeout for synchronizing data between the master server and the slave server , When this time is exceeded ,master The master server will stop all write operations on the client , The unit is in seconds 
 459 #
......
[[email protected] redis-5.0.4]# /etc/init.d/redis restart # restart redis
Stopping ...
Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe.
Redis stopped
Starting Redis server...
5291:C 09 Jun 2021 02:04:39.132 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
5291:C 09 Jun 2021 02:04:39.132 # Redis version=5.0.4, bits=64, commit=00000000, modified=0, pid=5291, just started
5291:C 09 Jun 2021 02:04:39.132 # Configuration loaded
Redis is running...

To configure slave Server master profile

[[email protected] redis-5.0.4]# vim /usr/local/redis/redis.conf 
......
 285 #
 286 replicaof 192.168.100.202 6379  # Specify the master server on the slave server ip And port 
 287 
......
 292 #
 293 masterauth 123123  # Specify the primary server redis Password 
 294
......
# Save and exit 
[[email protected] redis-5.0.4]# /etc/init.d/redis restart # Restart the service 
Stopping ...
Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe.
Redis stopped
Starting Redis server...
5304:C 09 Jun 2021 02:11:32.241 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
5304:C 09 Jun 2021 02:11:32.241 # Redis version=5.0.4, bits=64, commit=00000000, modified=0, pid=5304, just started
5304:C 09 Jun 2021 02:11:32.241 # Configuration loaded
Redis is running...

Verify master-slave replication

******（1） Log in to the main server redis, establish key
[[email protected] ~]# redis-cli -h 192.168.100.202 -a 123123
Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe.
192.168.100.202:6379> keys *
(empty list or set)
192.168.100.202:6379> set aaa bbb
OK
192.168.100.202:6379> keys *
1) "aaa"
192.168.100.202:6379> 

******（2） Switch to... From the server reids, See if it's syncing , And whether it can be written 
[[email protected] redis-5.0.4]# redis-cli -h 192.168.100.203 -a 123123
Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe.
192.168.100.203:6379> keys *
1) "aaa"
192.168.100.203:6379> set bbb ccc
(error) READONLY You can't write against a read only replica.  # Found unable to write data 


————————————————————————————————————————————————————
 Use info Command to view the replication information from the master server 
192.168.100.202:6379> info replication
# Replication
role:master
connected_slaves:1
min_slaves_good_slaves:1
slave0:ip=192.168.100.203,port=6379,state=online,offset=712,lag=0  #slave Information about 
master_replid:2550f57c98e18e6cb41d2c9172cc5ee5d2bbebfd
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:712
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:1
repl_backlog_histlen:712