Redis 主从复制可以实现数据库的读写分离，即主节点负责接收写请求、从节点负责接收读请求，是高性能 Redis 服务的基础。所以配置 Redis 主从复制应当作为开发者的技能之一，后文内容包括：

  1. 单机配置一主二从的主从复制服务
  2. 服务验证；

环境信息

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 20.04.2 LTS
Release:        20.04
Codename:       focal

$ redis-server -v
Redis server v=6.2.6 sha=00000000:0 malloc=jemalloc-5.1.0 bits=64 build=9c9e426e2f96cc51

配置过程

主节点使用 6379 端口，两个从节点分别使用 6380 和 6381 端口。

Redis 配置文件

复制两份 Redis 配置文件分别为两个从节点的配置文件：

cp -a /etc/redis/redis.conf /etc/redis/redis-server-6380.conf
cp -a /etc/redis/redis.conf /etc/redis/redis-server-6381.conf

修改两个配置文件的内容，修改及新增内容如下：

# redis-6380.conf
# 修改项
port 6380
pidfile /run/redis/redis-server-6380.pid
logfile /var/log/redis/redis-server-6380.log
dbfilename dump-6380.rdb
# 新增项
slaveof 127.0.0.1 6379

# redis-6381.conf
# 修改项
port 6381
pidfile /run/redis/redis-server-6381.pid
logfile /var/log/redis/redis-server-6381.log
dbfilename dump-6381.rdb
# 新增项
slaveof 127.0.0.1 6379

systemd 配置文件

复制两份 systemd 配置文件分别作为两个从节点的服务启动文件：

cp -a /lib/systemd/system/redis-server.service  /lib/systemd/system/redis-server-6380.service
cp -a /lib/systemd/system/redis-server.service  /lib/systemd/system/redis-server-6381.service

修改两个配置文件的内容，均为修改项，如下：

# redis-server-6380.service
[Service]
ExecStart=/usr/bin/redis-server /etc/redis/redis-server-6380.conf
PIDFile=/run/redis/redis-server-6380.pid

# redis-server-6381.service
[Service]
ExecStart=/usr/bin/redis-server /etc/redis/redis-server-6381.conf
PIDFile=/run/redis/redis-server-6381.pid

修改之后，需要执行如下命令进行重新加载：

systemctl daemon-reload

启动服务

配置完成后，通过 systemd 的管理命令分别在 3 个终端各启动 1 个服务，命令及显示如下：

# 主节点
$ systemctl start redis-server.service
$ redis-cli -p 6379
127.0.0.1:6379> INFO Replication
# Replication
role:master
connected_slaves:2
slave0:ip=127.0.0.1,port=6380,state=online,offset=308,lag=0
slave1:ip=127.0.0.1,port=6381,state=online,offset=308,lag=1
# 其它 ...

# 从节点 6380
$ systemctl start redis-server-6380.service
$ redis-cli -p 6380
127.0.0.1:6380> INFO Replication
# Replication
role:slave
master_host:127.0.0.1
master_port:6379
# 其它 ...

# 从节点 6381
$ systemctl start redis-server-6381.service
$ redis-cli -p 6381
127.0.0.1:6381> INFO Replication
# Replication
role:slave
master_host:127.0.0.1
master_port:6379
# 其它 ...

读写 Redis 数据库

是否发生主从复制，可按如下的命令依次执行进行验证。

# 主节点
127.0.0.1:6379> SET topic master-slave-replication
OK
# 从节点 6380
127.0.0.1:6380> GET topic
"master-slave-replication"
# 从节点 6381
127.0.0.1:6381> GET topic
"master-slave-replication"

其它

systemd 是 Linux 服务器管理服务的其中一种方式，服务的启动与关闭也可以通过 redis-server 命令或其它方式进行实现。Redis 使用到的目录及文件信息包括：

  • /run/redis/：存放 Redis 服务的 pid 文件，由 pidfile 配置项决定；
  • /var/log/redis/：存放 Redis 服务的日志文件，由 logfile 配置项决定；
  • /var/lib/redis：存放 RDB 文件，由 dir 和 dbfilename 配置项决定；

完整脚本

#!/bin/bash

SLAVE1_PORT=6380
SLAVE2_PORT=6381

cat /etc/redis/redis.conf | \
sed "s/^port\ 6379/port\ $SLAVE1_PORT/g" | \
sed "s/^pidfile \/run\/redis\/redis-server\.pid/pidfile \/run\/redis\/redis-server-$SLAVE1_PORT\.pid/g" | \
sed "s/^logfile \/var\/log\/redis\/redis-server\.log/logfile \/var\/log\/redis\/redis-server-$SLAVE1_PORT\.log/g" | \
sed "s/^dbfilename dump\.rdb/dbfilename dump-$SLAVE1_PORT\.rdb/g" | \
sed "\$a\\slaveof 127.0.0.1 6379\\" > /etc/redis/redis-server-$SLAVE1_PORT.conf
chown redis.redis /etc/redis/redis-server-$SLAVE1_PORT.conf

cat /etc/redis/redis.conf | \
sed "s/^port\ 6379/port\ $SLAVE2_PORT/g" | \
sed "s/^pidfile \/run\/redis\/redis-server\.pid/pidfile \/run\/redis\/redis-server-$SLAVE2_PORT\.pid/g" | \
sed "s/^logfile \/var\/log\/redis\/redis-server\.log/logfile \/var\/log\/redis\/redis-server-$SLAVE2_PORT\.log/g" | \
sed "s/^dbfilename dump\.rdb/dbfilename dump-$SLAVE2_PORT\.rdb/g" | \
sed "\$a\\slaveof 127.0.0.1 6379\\" > /etc/redis/redis-server-$SLAVE2_PORT.conf
chown redis.redis /etc/redis/redis-server-$SLAVE2_PORT.conf

cat /lib/systemd/system/redis-server.service | \
sed "s/\/etc\/redis\/redis\.conf/\/etc\/redis\/redis-server-$SLAVE1_PORT\.conf/g" | \
sed "s/\/run\/redis\/redis-server\.pid/\/run\/redis\/redis-server-$SLAVE1_PORT\.pid/g" > /lib/systemd/system/redis-server-$SLAVE1_PORT.service
chown root.root /lib/systemd/system/redis-server-$SLAVE1_PORT.service

cat /lib/systemd/system/redis-server.service | \
sed "s/\/etc\/redis\/redis\.conf/\/etc\/redis\/redis-server-$SLAVE2_PORT\.conf/g" | \
sed "s/\/run\/redis\/redis-server\.pid/\/run\/redis\/redis-server-$SLAVE2_PORT\.pid/g" > /lib/systemd/system/redis-server-$SLAVE2_PORT.service
chown root.root /lib/systemd/system/redis-server-$SLAVE2_PORT.service

systemctl daemon-reload

systemctl start redis-server.service
systemctl start redis-server-$SLAVE1_PORT.service
systemctl start redis-server-$SLAVE2_PORT.service

总结

  1. Redis 主从复制的配置过程；
  2. Redis 服务相关配置项说明；