一 副本集介绍

集群中每个节点有心跳检测

如果由于资源限制，可以部署一主一从一仲裁

副本集集群可以实现主从的自动切换

Read Preference

在客户端连接中，可以实现读取优先，就是连接器会自动判断，把读取请求发送到副本集中的从节点，默认读写都发送到主节点。

二 部署

下面使用部署 3 成员的副本集集群为例介绍副本集的部署。
并且假设，部署方式是 docker-compose

参考官方连接 https:///docs/manual/tutorial/deploy-replica-set-with-keyfile-access-control/

compose 文档内容如下:

version: '3.9'
services:
  # mongodb server
  mongo:
    labels:
      co.elastic.logs/module: mongodb
    image: mongo:6.0.4
    command: --replSet rs0 --bind_ip localhost,<hostname> --wiredTigerCacheSizeGB 2 --keyFile /etc/keyfile.key
    network_mode: host
    restart: always
    environment:
      # 管理员用户
      MONGO_INITDB_ROOT_USERNAME: mongoadmin

      # 管理员密码
      MONGO_INITDB_ROOT_PASSWORD: password
    volumes:
      - "/etc/localtime:/etc/localtime"
      - "./data:/data/db"
      - "./keyfile.key:/etc/keyfile.key"
    expose:
      - "27017:27017"

<hostname> 是每个节点的主机名

生成 密钥文件 用于集群成员之间的认证。 6.0 版本使用认证所必须的

openssl rand -base64 756 >

应该将集群的每个节点部署在不同的服务器上，这里假设部署的服务器主机名为： node1,node2,node3

mongdb 的 docker-compose 目前结构

mongodb:
  |- data
  |- keyfile.key
  |_ compose.yml

将 mongodb 目录传输到每个节点，并修改 keyfile.key 权限

chmod 400 keyfile.key
chown 999.999 keyfile.key  data

启动每个节点的 mongo 后，停 35 秒左右之后,只需在其中 任意一个节点执行如下命令初始化集群即可：

docker-compose exec mongo mongosh -u mongoadmin -p password --eval
          "rs.initiate({_id : 'rs0', members: [{ _id : 0, host: 'node1:27017' },{ _id : 1, host : 'node2:27017' },{ _id : 2, host : 'node3:27017' }]})"

检查集群状态
任意一个节点执行如下命令即可

docker-compose exec mongo mongosh -u root -p mongo123 --eval "rs.status()"

输出示例：
主要观察 stateStr 字段的值: PRIMARY|SECONDARY

...
 members: [
    {
      _id: 0,
      name: 'node1:27017',
      health: 1,
      state: 1,
      stateStr: 'PRIMARY',
      uptime: 1874,
      optime: { ts: Timestamp({ t: 1675232833, i: 1 }), t: Long("1") },
      optimeDate: ISODate("2023-02-01T06:27:13.000Z"),
      lastAppliedWallTime: ISODate("2023-02-01T06:27:13.799Z"),
      lastDurableWallTime: ISODate("2023-02-01T06:27:13.799Z"),
      syncSourceHost: '',
      syncSourceId: -1,
      infoMessage: '',
      electionTime: Timestamp({ t: 1675231003, i: 1 }),
      electionDate: ISODate("2023-02-01T05:56:43.000Z"),
      configVersion: 1,
      configTerm: 1,
      self: true,
      lastHeartbeatMessage: ''
    },
    {
      _id: 1,
      name: 'node2:27017',
      health: 1,
      state: 2,
      stateStr: 'SECONDARY',
      uptime: 1847,
      optime: { ts: Timestamp({ t: 1675232833, i: 1 }), t: Long("1") },
      optimeDurable: { ts: Timestamp({ t: 1675232833, i: 1 }), t: Long("1") },
      optimeDate: ISODate("2023-02-01T06:27:13.000Z"),
      optimeDurableDate: ISODate("2023-02-01T06:27:13.000Z"),
      lastAppliedWallTime: ISODate("2023-02-01T06:27:13.799Z"),
      lastDurableWallTime: ISODate("2023-02-01T06:27:13.799Z"),
      lastHeartbeat: ISODate("2023-02-01T06:27:19.573Z"),
      lastHeartbeatRecv: ISODate("2023-02-01T06:27:18.571Z"),
      pingMs: Long("0"),
      lastHeartbeatMessage: '',
      syncSourceHost: 'node1:27017',
      syncSourceId: 0,
      infoMessage: '',
      configVersion: 1,
      configTerm: 1
    },
    {
      _id: 2,
      name: 'node3:27017',
      health: 1,
      state: 2,
      stateStr: 'SECONDARY',
      uptime: 1847,
      optime: { ts: Timestamp({ t: 1675232833, i: 1 }), t: Long("1") },
      optimeDurable: { ts: Timestamp({ t: 1675232833, i: 1 }), t: Long("1") },
      optimeDate: ISODate("2023-02-01T06:27:13.000Z"),
      optimeDurableDate: ISODate("2023-02-01T06:27:13.000Z"),
      lastAppliedWallTime: ISODate("2023-02-01T06:27:13.799Z"),
      lastDurableWallTime: ISODate("2023-02-01T06:27:13.799Z"),
      lastHeartbeat: ISODate("2023-02-01T06:27:19.565Z"),
      lastHeartbeatRecv: ISODate("2023-02-01T06:27:18.593Z"),
      pingMs: Long("0"),
      lastHeartbeatMessage: '',
      syncSourceHost: 'node1:27017',
      syncSourceId: 0,
      infoMessage: '',
      configVersion: 1,
      configTerm: 1
    }
  ],
  ok: 1,
  '$clusterTime': {
    clusterTime: Timestamp({ t: 1675232833, i: 1 }),
    signature: {
      hash: Binary(Buffer.from("5d771f4d9b817a799ab4c221590e12a6da31c9b6", "hex"), 0),
      keyId: Long("7195062371130277893")
    }
  },
  operationTime: Timestamp({ t: 1675232833, i: 1 })
}