Mongodb副本集添加节点，你学会了吗？

1、准备工作

有一套mongodb 副本集的集群，部署方式参考 mongodb 4.0副本集搭建。

准备一个新节点，使用和原副本集版本一致的mongodb。

拷贝原副本集中的配置文件、keyfile文件，并注意修改keyfile文件的权限（600）。

节点	角色
192.168.56.199:27017	PRIMARY
192.168.56.198:27018	SECONDARY
192.168.56.199:27018	ARBITER

准备加入的新节点： 192.168.56.197:27017。

2、添加节点

（1）启动新节点

例如，原节点的版本是4.2.8，新节点版本一致，路径一致，然后启动新节点。

/usr/local/mongodb/bin/mongod -f /data/mongodb/27017/etc/mongodb.conf

（2）主库上查看当前节点及配置信息

使用rs.config()查看配置信息。

test12:PRIMARY>rs.config()
{
"_id" : "test12",
"version" : 1,
"protocolVersion" : NumberLong(1),
"writeConcernMajorityJournalDefault" : true,
"members" : [
    {
"_id" : 0,
"host" : "192.168.56.198:27017",
"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : false,
"priority" : 1,
"tags" : {


      },
"slaveDelay" : NumberLong(0),
"votes" : 1
    },
    {
"_id" : 1,
"host" : "192.168.56.199:27017",
"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : false,
"priority" : 1,
"tags" : {


      },
"slaveDelay" : NumberLong(0),
"votes" : 1
    },
    {
"_id" : 2,
"host" : "192.168.56.199:27018",
"arbiterOnly" : true,
"buildIndexes" : true,
"hidden" : false,
"priority" : 0,
"tags" : {


      },
"slaveDelay" : NumberLong(0),
"votes" : 1
    }
  ],
"settings" : {
"chainingAllowed" : true,
"heartbeatIntervalMillis" : 2000,
"heartbeatTimeoutSecs" : 10,
"electionTimeoutMillis" : 10000,
"catchUpTimeoutMillis" : -1,
"catchUpTakeoverDelayMillis" : 30000,
"getLastErrorModes" : {


    },
"getLastErrorDefaults" : {
"w" : 1,
"wtimeout" : 0
    },
"replicaSetId" : ObjectId("61b86af0a21015e69623e18d")
  }
}

rs.status() 查看状态信息。

test12:PRIMARY>rs.status()
{
"set" : "test12",
"date" : ISODate("2021-12-14T10:07:46.561Z"),
"myState" : 1,
"term" : NumberLong(1),
"syncingTo" : "",
"syncSourceHost" : "",
"syncSourceId" : -1,
"heartbeatIntervalMillis" : NumberLong(2000),
"majorityVoteCount" : 2,
"writeMajorityCount" : 2,
"optimes" : {
"lastCommittedOpTime" : {
"ts" : Timestamp(1639476462, 1),
"t" : NumberLong(1)
    },
"lastCommittedWallTime" : ISODate("2021-12-14T10:07:42.560Z"),
"readConcernMajorityOpTime" : {
"ts" : Timestamp(1639476462, 1),
"t" : NumberLong(1)
    },
"readConcernMajorityWallTime" : ISODate("2021-12-14T10:07:42.560Z"),
"appliedOpTime" : {
"ts" : Timestamp(1639476462, 1),
"t" : NumberLong(1)
    },
"durableOpTime" : {
"ts" : Timestamp(1639476462, 1),
"t" : NumberLong(1)
    },
"lastAppliedWallTime" : ISODate("2021-12-14T10:07:42.560Z"),
"lastDurableWallTime" : ISODate("2021-12-14T10:07:42.560Z")
  },
"lastStableRecoveryTimestamp" : Timestamp(1639476442, 1),
"lastStableCheckpointTimestamp" : Timestamp(1639476442, 1),
"electionCandidateMetrics" : {
"lastElectionReason" : "electionTimeout",
"lastElectionDate" : ISODate("2021-12-14T09:59:22.407Z"),
"electionTerm" : NumberLong(1),
"lastCommittedOpTimeAtElection" : {
"ts" : Timestamp(0, 0),
"t" : NumberLong(-1)
    },
"lastSeenOpTimeAtElection" : {
"ts" : Timestamp(1639475952, 1),
"t" : NumberLong(-1)
    },
"numVotesNeeded" : 2,
"priorityAtElection" : 1,
"electionTimeoutMillis" : NumberLong(10000),
"numCatchUpOps" : NumberLong(0),
"newTermStartDate" : ISODate("2021-12-14T09:59:22.431Z"),
"wMajorityWriteAvailabilityDate" : ISODate("2021-12-14T09:59:23.493Z")
  },
"members" : [
    {
"_id" : 0,
"name" : "192.168.56.198:27017",
"health" : 1,
"state" : 2,
"stateStr" : "SECONDARY",
"uptime" : 514,
"optime" : {
"ts" : Timestamp(1639476462, 1),
"t" : NumberLong(1)
      },
"optimeDurable" : {
"ts" : Timestamp(1639476462, 1),
"t" : NumberLong(1)
      },
"optimeDate" : ISODate("2021-12-14T10:07:42Z"),
"optimeDurableDate" : ISODate("2021-12-14T10:07:42Z"),
"lastHeartbeat" : ISODate("2021-12-14T10:07:45.153Z"),
"lastHeartbeatRecv" : ISODate("2021-12-14T10:07:46.542Z"),
"pingMs" : NumberLong(1),
"lastHeartbeatMessage" : "",
"syncingTo" : "192.168.56.199:27017",
"syncSourceHost" : "192.168.56.199:27017",
"syncSourceId" : 1,
"infoMessage" : "",
"configVersion" : 1
    },
    {
"_id" : 1,
"name" : "192.168.56.199:27017",
"health" : 1,
"state" : 1,
"stateStr" : "PRIMARY",
"uptime" : 1001,
"optime" : {
"ts" : Timestamp(1639476462, 1),
"t" : NumberLong(1)
      },
"optimeDate" : ISODate("2021-12-14T10:07:42Z"),
"syncingTo" : "",
"syncSourceHost" : "",
"syncSourceId" : -1,
"infoMessage" : "",
"electionTime" : Timestamp(1639475962, 1),
"electionDate" : ISODate("2021-12-14T09:59:22Z"),
"configVersion" : 1,
"self" : true,
"lastHeartbeatMessage" : ""
    },
    {
"_id" : 2,
"name" : "192.168.56.199:27018",
"health" : 1,
"state" : 7,
"stateStr" : "ARBITER",
"uptime" : 514,
"lastHeartbeat" : ISODate("2021-12-14T10:07:44.896Z"),
"lastHeartbeatRecv" : ISODate("2021-12-14T10:07:44.896Z"),
"pingMs" : NumberLong(0),
"lastHeartbeatMessage" : "",
"syncingTo" : "",
"syncSourceHost" : "",
"syncSourceId" : -1,
"infoMessage" : "",
"configVersion" : 1
    }
  ],
"ok" : 1,
"$clusterTime" : {
"clusterTime" : Timestamp(1639476462, 1),
"signature" : {
"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
"keyId" : NumberLong(0)
    }
  },
"operationTime" : Timestamp(1639476462, 1)
}

（3）将新节点添加至集群

在主库上执行rs.add()将新节点添加进集群中.

生产环境添加节点时，建议将priority及votes设为0,即不会选为主（priority默认1），也没有投票特性（votes默认1，有投票权）。

test12:PRIMARY> rs.add( { host: "192.168.56.197:27017", priority: 0, votes: 0 } )
{
  "ok" : 1,
  "$clusterTime" : {
    "clusterTime" : Timestamp(1639476997, 1),
    "signature" : {
      "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
      "keyId" : NumberLong(0)
    }
  },
  "operationTime" : Timestamp(1639476997, 1)
}

另外，生产环境是从主库拉取全量数据，如果数据量较大，则需要观察主库的压力及对线上业务的影响。

同步数据的过程中，新节点的状态stateStr 为STARTUP2，待同步完成后会变为SECONDARY。

（4）重置新节点的属性

此时再用rs.config()查看新节点状态，priority及votes是之前设的0，可以使用 rs.recofig()命令进行调整

test12:PRIMARY>rs.config()
{
"_id" : "test12",
"version" : 2,
"protocolVersion" : NumberLong(1),
"writeConcernMajorityJournalDefault" : true,
"members" : [
    {
"_id" : 0,
"host" : "192.168.56.198:27017",
"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : false,
"priority" : 1,
"tags" : {

      },
"slaveDelay" : NumberLong(0),
"votes" : 1
    },
    {
"_id" : 1,
"host" : "192.168.56.199:27017",
"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : false,
"priority" : 1,
"tags" : {

      },
"slaveDelay" : NumberLong(0),
"votes" : 1
    },
    {
"_id" : 2,
"host" : "192.168.56.199:27018",
"arbiterOnly" : true,
"buildIndexes" : true,
"hidden" : false,
"priority" : 0,
"tags" : {

      },
"slaveDelay" : NumberLong(0),
"votes" : 1
    },
    {
"_id" : 3,
"host" : "192.168.56.197:27017",
"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : false,
"priority" : 0,
"tags" : {

      },
"slaveDelay" : NumberLong(0),
"votes" : 0
    }
  ],
"settings" : {
"chainingAllowed" : true,
"heartbeatIntervalMillis" : 2000,
"heartbeatTimeoutSecs" : 10,
"electionTimeoutMillis" : 10000,
"catchUpTimeoutMillis" : -1,
"catchUpTakeoverDelayMillis" : 30000,
"getLastErrorModes" : {

    },
"getLastErrorDefaults" : {
"w" : 1,
"wtimeout" : 0
    },
"replicaSetId" : ObjectId("61b86af0a21015e69623e18d")
  }
}

从上面可以看到新节点的id为3 ，则可以通过如下命令调整对应的属性。

varcfg=rs.conf()
cfg.members[3].priority=1
cfg.members[3].votes=1
rs.reconfig(cfg)

调整后再查看，属性已调整。

test12:PRIMARY>rs.config()
{
"_id" : "test12",
"version" : 3,
"protocolVersion" : NumberLong(1),
"writeConcernMajorityJournalDefault" : true,
"members" : [
    {
"_id" : 0,
"host" : "192.168.56.198:27017",
"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : false,
"priority" : 1,
"tags" : {

      },
"slaveDelay" : NumberLong(0),
"votes" : 1
    },
    {
"_id" : 1,
"host" : "192.168.56.199:27017",
"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : false,
"priority" : 1,
"tags" : {

      },
"slaveDelay" : NumberLong(0),
"votes" : 1
    },
    {
"_id" : 2,
"host" : "192.168.56.199:27018",
"arbiterOnly" : true,
"buildIndexes" : true,
"hidden" : false,
"priority" : 0,
"tags" : {

      },
"slaveDelay" : NumberLong(0),
"votes" : 1
    },
    {
"_id" : 3,
"host" : "192.168.56.197:27017",
"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : false,
"priority" : 1,
"tags" : {

      },
"slaveDelay" : NumberLong(0),
"votes" : 1
    }
  ],
"settings" : {
"chainingAllowed" : true,
"heartbeatIntervalMillis" : 2000,
"heartbeatTimeoutSecs" : 10,
"electionTimeoutMillis" : 10000,
"catchUpTimeoutMillis" : -1,
"catchUpTakeoverDelayMillis" : 30000,
"getLastErrorModes" : {

    },
"getLastErrorDefaults" : {
"w" : 1,
"wtimeout" : 0
    },
"replicaSetId" : ObjectId("61b86af0a21015e69623e18d")
  }
}

至此，新节点便加入了副本集中。

3、注意点总结

一个副本集，最多可以拥有50个secondary，最多可以有7个投票成员，在副本集里面添加一个新成员，如果之前副本集已经有了7个成员，那么可以设置成非投票成员，或者你从移除之前一个投票成员出来。
新节点的版本、配置建议与原集群一致。
注意添加新节点前确定网络互通。
如果集群数据量较大，则选择业务低峰期添加节点，并观察压力情况。
新节点加入时建议将priority及votes设为0。

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