mongodb副本集添加节点
mongodb副本集架构运行一段时间后如果业务发展需要新增新的成员，或者迁移集群，则可以参考本文处理
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
2.1 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.conf2.2 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")}}
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,"$clusterTime" : {"clusterTime" : Timestamp(1639476462, 1),"signature" : {"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),"keyId" : NumberLong(0)}},"operationTime" : Timestamp(1639476462, 1)}
2.3 将新节点添加至集群
在主库上执行rs.add()将新节点添加进集群中
生产环境添加节点时，建议将priority及votes设为0,即不会选为主（priority默认1），也没有投票特性（votes默认1，有投票权）
test12:PRIMARY> rs.add( { host: "192.168.56.197:27017", priority: 0, votes: 0 } ){"ok" : 1,"$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。
2.4 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
var cfg = rs.conf()cfg.members[3].priority = 1cfg.members[3].votes = 1rs.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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