MongoDB副本集调整节点
MongoDB的副本集（Replica Set）是一个高可用性、可扩展性和冗余性的数据库解决方案。它能够确保数据库的高可用性，同时保障了数据的安全性。在本文中，我们将探讨如何在一个已经包含三个数据节点的副本集集群中，添加一个仲裁节点，并同时删除原先的一个数据节点。
1、副本集的基本概念
MongoDB副本集由多个数据节点+若干个仲裁节点（可以没有）组成，其中一个数据节点被选举为主节点(Primary），其余节点为次要节点（Secondary）。在故障时，副本集会自动进行主节点的切换，确保服务的高可用性。副本集中的仲裁节点（Arbiter）不存储数据，仅用于选举过程，帮助副本集进行决策。
例如，当前配置一个3节点的数据节点集群，组件集群命令如下：
> use admin > rs.initiate( {_id: "test1",members: [{ _id: 0, host: "192.168.122.36:27017" },{ _id: 1, host: "192.168.122.36:27018" },{ _id: 2, host: "192.168.122.36:27019" } ] })
查看状态：
test1:PRIMARY> use admin switched to db admin test1:PRIMARY> rs.status() { "set" : "test1", "date" : ISODate("2023-10-23T02:31:02.345Z"), "myState" : 1, "term" : NumberLong(1), "syncingTo" : "", "syncSourceHost" : "", "syncSourceId" : -1, "heartbeatIntervalMillis" : NumberLong(2000), "majorityVoteCount" : 2, "writeMajorityCount" : 2, "optimes" : { "lastCommittedOpTime" : { "ts" : Timestamp(1698028254, 1), "t" : NumberLong(1) }, "lastCommittedWallTime" : ISODate("2023-10-23T02:30:54.919Z"), "readConcernMajorityOpTime" : { "ts" : Timestamp(1698028254, 1), "t" : NumberLong(1) }, "readConcernMajorityWallTime" : ISODate("2023-10-23T02:30:54.919Z"), "appliedOpTime" : { "ts" : Timestamp(1698028254, 1), "t" : NumberLong(1) }, "durableOpTime" : { "ts" : Timestamp(1698028254, 1), "t" : NumberLong(1) }, "lastAppliedWallTime" : ISODate("2023-10-23T02:30:54.919Z"), "lastDurableWallTime" : ISODate("2023-10-23T02:30:54.919Z") }, "lastStableRecoveryTimestamp" : Timestamp(1698028224, 3), "lastStableCheckpointTimestamp" : Timestamp(1698028224, 3), "electionCandidateMetrics" : { "lastElectionReason" : "electionTimeout", "lastElectionDate" : ISODate("2023-10-23T02:30:24.838Z"), "electionTerm" : NumberLong(1), "lastCommittedOpTimeAtElection" : { "ts" : Timestamp(0, 0), "t" : NumberLong(-1) }, "lastSeenOpTimeAtElection" : { "ts" : Timestamp(1698028214, 1), "t" : NumberLong(-1) }, "numVotesNeeded" : 2, "priorityAtElection" : 1, "electionTimeoutMillis" : NumberLong(10000), "numCatchUpOps" : NumberLong(0), "newTermStartDate" : ISODate("2023-10-23T02:30:24.912Z"), "wMajorityWriteAvailabilityDate" : ISODate("2023-10-23T02:30:25.497Z") }, "members" : [ { "_id" : 0, "name" : "192.168.122.36:27017", "health" : 1, "state" : 1, "stateStr" : "PRIMARY", "uptime" : 183, "optime" : { "ts" : Timestamp(1698028254, 1), "t" : NumberLong(1) }, "optimeDate" : ISODate("2023-10-23T02:30:54Z"), "syncingTo" : "", "syncSourceHost" : "", "syncSourceId" : -1, "infoMessage" : "could not find member to sync from", "electionTime" : Timestamp(1698028224, 1), "electionDate" : ISODate("2023-10-23T02:30:24Z"), "configVersion" : 1, "self" : true, "lastHeartbeatMessage" : "" }, { "_id" : 1, "name" : "192.168.122.36:27018", "health" : 1, "state" : 2, "stateStr" : "SECONDARY", "uptime" : 47, "optime" : { "ts" : Timestamp(1698028254, 1), "t" : NumberLong(1) }, "optimeDurable" : { "ts" : Timestamp(1698028254, 1), "t" : NumberLong(1) }, "optimeDate" : ISODate("2023-10-23T02:30:54Z"), "optimeDurableDate" : ISODate("2023-10-23T02:30:54Z"), "lastHeartbeat" : ISODate("2023-10-23T02:31:00.889Z"), "lastHeartbeatRecv" : ISODate("2023-10-23T02:31:01.443Z"), "pingMs" : NumberLong(0), "lastHeartbeatMessage" : "", "syncingTo" : "192.168.122.36:27017", "syncSourceHost" : "192.168.122.36:27017", "syncSourceId" : 0, "infoMessage" : "", "configVersion" : 1 }, { "_id" : 2, "name" : "192.168.122.36:27019", "health" : 1, "state" : 2, "stateStr" : "SECONDARY", "uptime" : 47, "optime" : { "ts" : Timestamp(1698028254, 1), "t" : NumberLong(1) }, "optimeDurable" : { "ts" : Timestamp(1698028254, 1), "t" : NumberLong(1) }, "optimeDate" : ISODate("2023-10-23T02:30:54Z"), "optimeDurableDate" : ISODate("2023-10-23T02:30:54Z"), "lastHeartbeat" : ISODate("2023-10-23T02:31:00.890Z"), "lastHeartbeatRecv" : ISODate("2023-10-23T02:31:01.446Z"), "pingMs" : NumberLong(0), "lastHeartbeatMessage" : "", "syncingTo" : "192.168.122.36:27017", "syncSourceHost" : "192.168.122.36:27017", "syncSourceId" : 0, "infoMessage" : "", "configVersion" : 1 } ], "ok" : 1, "$clusterTime" : { "clusterTime" : Timestamp(1698028254, 1), "signature" : { "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId" : NumberLong(0) } }, "operationTime" : Timestamp(1698028254, 1) }
此时可以用一个程序验证集群的可用情况：
from pymongo import MongoClient from pymongo.errors import ConnectionFailure # MongoDB副本集的连接信息 replica_set = "test1" mongo_host = ["192.168.122.36:27017", "192.168.122.36:27018", "192.168.122.36:27019"] # 主机和端口号列表 # 尝试连接MongoDB副本集 try: client = MongoClient(mongo_host, replicaSet=replica_set, serverSelectinotallow=5000) db = client["testdb"] print("Successfully connected to MongoDB replica set.") collection = db['test1'] data = {"b":2} result = collection.insert_one(data) except ConnectionFailure: print("Failed to connect to MongoDB replica set. Please check your connection settings.")
运行结果如下：
查看数据库中运行结果：
2、添加节点
要添加一个仲裁节点，我们需要在现有副本集中的任一节点上执行如下操作：
rs.add( { host: "IP:PORT", arbiterOnly:true } )执行这个命令后，MongoDB将会在副本集中添加一个仲裁节点，增加了选主的稳定性，同时不会增加数据存储的压力。具体实际案例如下
test1:PRIMARY> use admin switched to db admin test1:PRIMARY> rs.add( { host: "192.168.122.36:27020", arbiterOnly:true } ) { "ok" : 1, "$clusterTime" : { "clusterTime" : Timestamp(1698030806, 1), "signature" : { "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId" : NumberLong(0) } }, "operationTime" : Timestamp(1698030806, 1) } test1:PRIMARY> rs.status(); { "set" : "test1", "date" : ISODate("2023-10-23T03:13:32.511Z"), "myState" : 1, "term" : NumberLong(1), "syncingTo" : "", "syncSourceHost" : "", "syncSourceId" : -1, "heartbeatIntervalMillis" : NumberLong(2000), "majorityVoteCount" : 3, "writeMajorityCount" : 3, "optimes" : { "lastCommittedOpTime" : { "ts" : Timestamp(1698030806, 1), "t" : NumberLong(1) }, "lastCommittedWallTime" : ISODate("2023-10-23T03:13:26.379Z"), "readConcernMajorityOpTime" : { "ts" : Timestamp(1698030806, 1), "t" : NumberLong(1) }, "readConcernMajorityWallTime" : ISODate("2023-10-23T03:13:26.379Z"), "appliedOpTime" : { "ts" : Timestamp(1698030806, 1), "t" : NumberLong(1) }, "durableOpTime" : { "ts" : Timestamp(1698030806, 1), "t" : NumberLong(1) }, "lastAppliedWallTime" : ISODate("2023-10-23T03:13:26.379Z"), "lastDurableWallTime" : ISODate("2023-10-23T03:13:26.379Z") }, "lastStableRecoveryTimestamp" : Timestamp(1698030805, 1), "lastStableCheckpointTimestamp" : Timestamp(1698030805, 1), "electionCandidateMetrics" : { "lastElectionReason" : "electionTimeout", "lastElectionDate" : ISODate("2023-10-23T02:30:24.838Z"), "electionTerm" : NumberLong(1), "lastCommittedOpTimeAtElection" : { "ts" : Timestamp(0, 0), "t" : NumberLong(-1) }, "lastSeenOpTimeAtElection" : { "ts" : Timestamp(1698028214, 1), "t" : NumberLong(-1) }, "numVotesNeeded" : 2, "priorityAtElection" : 1, "electionTimeoutMillis" : NumberLong(10000), "numCatchUpOps" : NumberLong(0), "newTermStartDate" : ISODate("2023-10-23T02:30:24.912Z"), "wMajorityWriteAvailabilityDate" : ISODate("2023-10-23T02:30:25.497Z") }, "members" : [ { "_id" : 0, "name" : "192.168.122.36:27017", "health" : 1, "state" : 1, "stateStr" : "PRIMARY", "uptime" : 2733, "optime" : { "ts" : Timestamp(1698030806, 1), "t" : NumberLong(1) }, "optimeDate" : ISODate("2023-10-23T03:13:26Z"), "syncingTo" : "", "syncSourceHost" : "", "syncSourceId" : -1, "infoMessage" : "", "electionTime" : Timestamp(1698028224, 1), "electionDate" : ISODate("2023-10-23T02:30:24Z"), "configVersion" : 2, "self" : true, "lastHeartbeatMessage" : "" }, { "_id" : 1, "name" : "192.168.122.36:27018", "health" : 1, "state" : 2, "stateStr" : "SECONDARY", "uptime" : 2597, "optime" : { "ts" : Timestamp(1698030806, 1), "t" : NumberLong(1) }, "optimeDurable" : { "ts" : Timestamp(1698030806, 1), "t" : NumberLong(1) }, "optimeDate" : ISODate("2023-10-23T03:13:26Z"), "optimeDurableDate" : ISODate("2023-10-23T03:13:26Z"), "lastHeartbeat" : ISODate("2023-10-23T03:13:32.393Z"), "lastHeartbeatRecv" : ISODate("2023-10-23T03:13:32.420Z"), "pingMs" : NumberLong(1), "lastHeartbeatMessage" : "", "syncingTo" : "", "syncSourceHost" : "", "syncSourceId" : -1, "infoMessage" : "", "configVersion" : 2 }, { "_id" : 2, "name" : "192.168.122.36:27019", "health" : 1, "state" : 2, "stateStr" : "SECONDARY", "uptime" : 2597, "optime" : { "ts" : Timestamp(1698030806, 1), "t" : NumberLong(1) }, "optimeDurable" : { "ts" : Timestamp(1698030806, 1), "t" : NumberLong(1) }, "optimeDate" : ISODate("2023-10-23T03:13:26Z"), "optimeDurableDate" : ISODate("2023-10-23T03:13:26Z"), "lastHeartbeat" : ISODate("2023-10-23T03:13:32.393Z"), "lastHeartbeatRecv" : ISODate("2023-10-23T03:13:32.445Z"), "pingMs" : NumberLong(1), "lastHeartbeatMessage" : "", "syncingTo" : "", "syncSourceHost" : "", "syncSourceId" : -1, "infoMessage" : "", "configVersion" : 2 }, { "_id" : 3, "name" : "192.168.122.36:27020", "health" : 1, "state" : 7, "stateStr" : "ARBITER", "uptime" : 6, "lastHeartbeat" : ISODate("2023-10-23T03:13:32.405Z"), "lastHeartbeatRecv" : ISODate("2023-10-23T03:13:32.455Z"), "pingMs" : NumberLong(4), "lastHeartbeatMessage" : "", "syncingTo" : "", "syncSourceHost" : "", "syncSourceId" : -1, "infoMessage" : "", "configVersion" : 2 } ], "ok" : 1, "$clusterTime" : { "clusterTime" : Timestamp(1698030806, 1), "signature" : { "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId" : NumberLong(0) } }, "operationTime" : Timestamp(1698030806, 1) }
此时修改python中程序（插入的数据），运行结果如下：
3、删除数据节点
如果你需要删除一个数据节点，首先，你要确保副本集的健康状态，然后执行如下操作来删除一个Secondary节点。
rs.remove("IP:PORT");执行这个命令后，MongoDB将从副本集中移除该数据节点，副本集会重新进行选举，确保副本集的高可用性。
test1:PRIMARY> rs.remove("192.168.122.36:27019") { "ok" : 1, "$clusterTime" : { "clusterTime" : Timestamp(1698038888, 1), "signature" : { "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId" : NumberLong(0) } }, "operationTime" : Timestamp(1698038888, 1) } test1:PRIMARY> rs.status function() { return db._adminCommand("replSetGetStatus"); # 选举中 } test1:PRIMARY> rs.status() { "set" : "test1", "date" : ISODate("2023-10-23T05:28:15.398Z"), "myState" : 1, "term" : NumberLong(1), "syncingTo" : "", "syncSourceHost" : "", "syncSourceId" : -1, "heartbeatIntervalMillis" : NumberLong(2000), "majorityVoteCount" : 2, "writeMajorityCount" : 2, "optimes" : { "lastCommittedOpTime" : { "ts" : Timestamp(1698038888, 1), "t" : NumberLong(1) }, "lastCommittedWallTime" : ISODate("2023-10-23T05:28:08.335Z"), "readConcernMajorityOpTime" : { "ts" : Timestamp(1698038888, 1), "t" : NumberLong(1) }, "readConcernMajorityWallTime" : ISODate("2023-10-23T05:28:08.335Z"), "appliedOpTime" : { "ts" : Timestamp(1698038888, 1), "t" : NumberLong(1) }, "durableOpTime" : { "ts" : Timestamp(1698038888, 1), "t" : NumberLong(1) }, "lastAppliedWallTime" : ISODate("2023-10-23T05:28:08.335Z"), "lastDurableWallTime" : ISODate("2023-10-23T05:28:08.335Z") }, "lastStableRecoveryTimestamp" : Timestamp(1698038845, 1), "lastStableCheckpointTimestamp" : Timestamp(1698038845, 1), "electionCandidateMetrics" : { "lastElectionReason" : "electionTimeout", "lastElectionDate" : ISODate("2023-10-23T02:30:24.838Z"), "electionTerm" : NumberLong(1), "lastCommittedOpTimeAtElection" : { "ts" : Timestamp(0, 0), "t" : NumberLong(-1) }, "lastSeenOpTimeAtElection" : { "ts" : Timestamp(1698028214, 1), "t" : NumberLong(-1) }, "numVotesNeeded" : 2, "priorityAtElection" : 1, "electionTimeoutMillis" : NumberLong(10000), "numCatchUpOps" : NumberLong(0), "newTermStartDate" : ISODate("2023-10-23T02:30:24.912Z"), "wMajorityWriteAvailabilityDate" : ISODate("2023-10-23T02:30:25.497Z") }, "members" : [ { "_id" : 0, "name" : "192.168.122.36:27017", "health" : 1, "state" : 1, "stateStr" : "PRIMARY", "uptime" : 10816, "optime" : { "ts" : Timestamp(1698038888, 1), "t" : NumberLong(1) }, "optimeDate" : ISODate("2023-10-23T05:28:08Z"), "syncingTo" : "", "syncSourceHost" : "", "syncSourceId" : -1, "infoMessage" : "", "electionTime" : Timestamp(1698028224, 1), "electionDate" : ISODate("2023-10-23T02:30:24Z"), "configVersion" : 3, "self" : true, "lastHeartbeatMessage" : "" }, { "_id" : 1, "name" : "192.168.122.36:27018", "health" : 1, "state" : 2, "stateStr" : "SECONDARY", "uptime" : 10680, "optime" : { "ts" : Timestamp(1698038888, 1), "t" : NumberLong(1) }, "optimeDurable" : { "ts" : Timestamp(1698038888, 1), "t" : NumberLong(1) }, "optimeDate" : ISODate("2023-10-23T05:28:08Z"), "optimeDurableDate" : ISODate("2023-10-23T05:28:08Z"), "lastHeartbeat" : ISODate("2023-10-23T05:28:14.347Z"), "lastHeartbeatRecv" : ISODate("2023-10-23T05:28:15.388Z"), "pingMs" : NumberLong(1), "lastHeartbeatMessage" : "", "syncingTo" : "", "syncSourceHost" : "", "syncSourceId" : -1, "infoMessage" : "", "configVersion" : 3 }, { "_id" : 3, "name" : "192.168.122.36:27020", "health" : 1, "state" : 7, "stateStr" : "ARBITER", "uptime" : 8088, "lastHeartbeat" : ISODate("2023-10-23T05:28:14.342Z"), "lastHeartbeatRecv" : ISODate("2023-10-23T05:28:14.369Z"), "pingMs" : NumberLong(0), "lastHeartbeatMessage" : "", "syncingTo" : "", "syncSourceHost" : "", "syncSourceId" : -1, "infoMessage" : "", "configVersion" : 3 } ], "ok" : 1, "$clusterTime" : { "clusterTime" : Timestamp(1698038888, 1), "signature" : { "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId" : NumberLong(0) } }, "operationTime" : Timestamp(1698038888, 1) }
注意：复制集将会短暂的关闭连接并进入选举，选举出一个新的主节点。接口将会自动重连。接口可能将会报错 DBClientCursor::init call() failed 。
