docker compose部署主从复制的实现

受限于 redis 单点性能，加上我们对数据天生就有的备份的需求，因此 redis 提供了主从复制的服务。

本文记录了通过 docker compose 搭建一主双从的 redis 服务。

配置解析

################################# replication #################################

# 【slave】连接 master 的配置
# slaveof 172.25.0.101 6379

# 【slave】只读模式
# slave-read-only yes

# 【slave】密码
# masterauth <master-password>

# 【slave】复制期间是否允许响应查询，可能会返回脏数据
# slave-serve-stale-data yes

# 【slave】slave 晋级为 master 的优先级，仅哨兵模式下生效
# slave-priority 100

# 【slave】slave 向 master 报告的自己的 ip
# slave-announce-ip 5.5.5.5

# 【slave】slave 向 master 报告的自己的端口
# slave-announce-port 1234

# 【slave】slave ping master 的时间间隔
# repl-ping-slave-period 10

# 【master/slave】超时时间
# repl-timeout 60

# 【master】diskless 就是直接将要复制的 rdb 文件写入到 socket 中，而不会先存储到磁盘上
repl-diskless-sync no

# 【master】若开启 diskless，会等待指定秒之后再进行复制，以便让更多客户端可以在窗口期内连接，并行传送
# repl-diskless-sync-delay 5

# 【master】是否开启 nagle 算法，可以减少流量占用，但会同步得慢些
repl-disable-tcp-nodelay no

# 【master】环形缓冲日志的大小，给 slave 断开之后重连使用，避免全量复制，默认 1mb
# repl-backlog-size 1mb

# 【master】当 master 断连所有 slave 指定时间后，master 会清空 backlog
# repl-backlog-ttl 3600

# 【master】当低于指定个 slave 连接时，master 拒绝所有写操作
# min-slaves-to-write 3

# 【master】当延迟高于指定秒数时，master 拒绝所有写操作
# min-slaves-max-lag 10

服务搭建

目录结构

replication/
├── docker-compose.yml
├── master
│   ├── data
│   └── redis.conf
├── slave1
│   ├── data
│   └── redis.conf
└── slave2
    ├── data
    └── redis.conf

compose file

定义了一个子网，方便操作，对外暴露 6371（master）、6372、6373 端口。

version: "3"

networks:
  redis-replication:
    driver: bridge
    ipam:
      config:
        - subnet: 172.25.0.0/24

services:
  master:
    image: redis
    container_name: redis-master
    ports:
      - "6371:6379"
    volumes:
      - "./master/redis.conf:/etc/redis.conf"
      - "./master/data:/data"
    command: ["redis-server", "/etc/redis.conf"]
    restart: always
    networks:
      redis-replication:
        ipv4_address: 172.25.0.101

  slave1:
    image: redis
    container_name: redis-slave-1
    ports:
      - "6372:6379"
    volumes:
      - "./slave1/redis.conf:/etc/redis.conf"
      - "./slave1/data:/data"
    command: ["redis-server", "/etc/redis.conf"]
    restart: always
    networks:
      redis-replication:
        ipv4_address: 172.25.0.102

  slave2:
    image: redis
    container_name: redis-slave-2
    ports:
      - "6373:6379"
    volumes:
      - "./slave2/redis.conf:/etc/redis.conf"
      - "./slave2/data:/data"
    command: ["redis-server", "/etc/redis.conf"]
    restart: always
    networks:
      redis-replication:
        ipv4_address: 172.25.0.103

实例配置

master：

基本不用配置，最简单的是指定一个端口就好了。

port 6379
protected-mode no

repl-diskless-sync no
repl-disable-tcp-nodelay no

slave：

实例的配置保持一致就可以了，因为定义了子网，不存在端口冲突。

port 6379
protected-mode no

slaveof 172.25.0.101 6379
slave-read-only yes
slave-serve-stale-data yes

启动服务

ocker-compose up -d
creating network "replication_redis-replication" with driver "bridge"
creating redis-slave-1 ... done
creating redis-master  ... done
creating redis-slave-2 ... done

查看 master 日志，可以看到接受了两个 slave 的复制请求：

1:m 18 aug 2021 15:50:31.772 * replica 172.25.0.102:6379 asks for synchronization
1:m 18 aug 2021 15:50:31.772 * full resync requested by replica 172.25.0.102:6379
1:m 18 aug 2021 15:50:31.772 * replication backlog created, my new replication ids are '5d27746f14ee9be9694d794f96de6ba14a669dd1' and '0000000000000000000000000000000000000000'
1:m 18 aug 2021 15:50:31.772 * starting bgsave for sync with target: disk
1:m 18 aug 2021 15:50:31.773 * background saving started by pid 19
19:c 18 aug 2021 15:50:31.777 * db saved on disk
19:c 18 aug 2021 15:50:31.777 * rdb: 0 mb of memory used by copy-on-write
1:m 18 aug 2021 15:50:31.822 * background saving terminated with success
1:m 18 aug 2021 15:50:31.823 * synchronization with replica 172.25.0.102:6379 succeeded
1:m 18 aug 2021 15:50:32.170 * replica 172.25.0.103:6379 asks for synchronization
1:m 18 aug 2021 15:50:32.170 * full resync requested by replica 172.25.0.103:6379
1:m 18 aug 2021 15:50:32.170 * starting bgsave for sync with target: disk
1:m 18 aug 2021 15:50:32.171 * background saving started by pid 20
20:c 18 aug 2021 15:50:32.175 * db saved on disk
20:c 18 aug 2021 15:50:32.175 * rdb: 0 mb of memory used by copy-on-write
1:m 18 aug 2021 15:50:32.225 * background saving terminated with success
1:m 18 aug 2021 15:50:32.226 * synchronization with replica 172.25.0.103:6379 succeeded

查看 slave 日志，可以看到连接建立的全过程：

1:s 18 aug 2021 15:50:31.771 * connecting to master 172.25.0.101:6379
1:s 18 aug 2021 15:50:31.771 * master <-> replica sync started
1:s 18 aug 2021 15:50:31.771 * non blocking connect for sync fired the event.
1:s 18 aug 2021 15:50:31.771 * master replied to ping, replication can continue...
1:s 18 aug 2021 15:50:31.772 * partial resynchronization not possible (no cached master)
1:s 18 aug 2021 15:50:31.773 * full resync from master: 5d27746f14ee9be9694d794f96de6ba14a669dd1:0
1:s 18 aug 2021 15:50:31.823 * master <-> replica sync: receiving 175 bytes from master to disk
1:s 18 aug 2021 15:50:31.823 * master <-> replica sync: flushing old data
1:s 18 aug 2021 15:50:31.823 * master <-> replica sync: loading db in memory
1:s 18 aug 2021 15:50:31.828 * loading rdb produced by version 6.2.5
1:s 18 aug 2021 15:50:31.828 * rdb age 0 seconds
1:s 18 aug 2021 15:50:31.828 * rdb memory usage when created 1.83 mb
1:s 18 aug 2021 15:50:31.829 * master <-> replica sync: finished with success

测试

登录 master，尝试写入新 key。

127.0.0.1:6371> set hello world
ok

登录 slave，查看能否读取到：

127.0.0.1:6372> get hello
"world"

slave 尝试写操作：

127.0.0.1:6372> set hello redis
(error) readonly you can't write against a read only replica.

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