从节点宕机 集群依然可以正常使用，可以读写操作。
docker ps三个容器均工作正常 （mongo01为主库，mongo02，mongo01为复制库） 此时手动停止mongo02容器
docker stop mongo02进入容器，测试读写是否正常 主库插入
rs0:PRIMARY> use test switched to db test rs0:PRIMARY> db.user.insert({"id":1002,"name":"lisi"}) WriteResult({ "nInserted" : 1 })复制库读取
rs0:SECONDARY> use test switched to db test rs0:SECONDARY> db.user.find() { "_id" : ObjectId("5f90f9c2d5a6806dd78d4879"), "id" : 1001, "name" : "zhangsan" } { "_id" : ObjectId("5f90fce6eaa4dcf95a6efb6f"), "id" : 1002, "name" : "lisi" }主节点宕机 选举出新的主节点继续提供服务 我们开启mongo02
docker start mongo02关闭主库
docker stop mongo01进入容器，查看复制集状态
docker exec -it mongo02 /bin/bash mongo rs.status()响应如下，可以看到节点一已经下线了，节点二被选举为主节点
{ "set" : "rs0", "date" : ISODate("2020-10-22T03:36:10.917Z"), "myState" : 1, "term" : NumberLong(2), "syncSourceHost" : "", "syncSourceId" : -1, "heartbeatIntervalMillis" : NumberLong(2000), "majorityVoteCount" : 2, "writeMajorityCount" : 2, "votingMembersCount" : 3, "writableVotingMembersCount" : 3, "optimes" : { "lastCommittedOpTime" : { "ts" : Timestamp(1603337761, 1), "t" : NumberLong(2) }, "lastCommittedWallTime" : ISODate("2020-10-22T03:36:01.825Z"), "readConcernMajorityOpTime" : { "ts" : Timestamp(1603337761, 1), "t" : NumberLong(2) }, "readConcernMajorityWallTime" : ISODate("2020-10-22T03:36:01.825Z"), "appliedOpTime" : { "ts" : Timestamp(1603337761, 1), "t" : NumberLong(2) }, "durableOpTime" : { "ts" : Timestamp(1603337761, 1), "t" : NumberLong(2) }, "lastAppliedWallTime" : ISODate("2020-10-22T03:36:01.825Z"), "lastDurableWallTime" : ISODate("2020-10-22T03:36:01.825Z") }, "lastStableRecoveryTimestamp" : Timestamp(1603337705, 1), "electionCandidateMetrics" : { "lastElectionReason" : "stepUpRequestSkipDryRun", "lastElectionDate" : ISODate("2020-10-22T03:34:00.775Z"), "electionTerm" : NumberLong(2), "lastCommittedOpTimeAtElection" : { "ts" : Timestamp(1603337639, 1), "t" : NumberLong(1) }, "lastSeenOpTimeAtElection" : { "ts" : Timestamp(1603337639, 1), "t" : NumberLong(1) }, "numVotesNeeded" : 2, "priorityAtElection" : 1, "electionTimeoutMillis" : NumberLong(10000), "priorPrimaryMemberId" : 0, "numCatchUpOps" : NumberLong(0), "newTermStartDate" : ISODate("2020-10-22T03:34:01.808Z"), "wMajorityWriteAvailabilityDate" : ISODate("2020-10-22T03:34:02.794Z") }, "members" : [ { "_id" : 0, "name" : "192.168.130.128:27017", "health" : 0, "state" : 8, "stateStr" : "(not reachable/healthy)", "uptime" : 0, "optime" : { "ts" : Timestamp(0, 0), "t" : NumberLong(-1) }, "optimeDurable" : { "ts" : Timestamp(0, 0), "t" : NumberLong(-1) }, "optimeDate" : ISODate("1970-01-01T00:00:00Z"), "optimeDurableDate" : ISODate("1970-01-01T00:00:00Z"), "lastHeartbeat" : ISODate("2020-10-22T03:36:10.024Z"), "lastHeartbeatRecv" : ISODate("2020-10-22T03:34:00.276Z"), "pingMs" : NumberLong(0), "lastHeartbeatMessage" : "Error connecting to 192.168.130.128:27017 :: caused by :: Connection refused", "syncSourceHost" : "", "syncSourceId" : -1, "infoMessage" : "", "configVersion" : 1, "configTerm" : 1 }, { "_id" : 1, "name" : "192.168.130.128:27018", "health" : 1, "state" : 1, "stateStr" : "PRIMARY", "uptime" : 176, "optime" : { "ts" : Timestamp(1603337761, 1), "t" : NumberLong(2) }, "optimeDate" : ISODate("2020-10-22T03:36:01Z"), "syncSourceHost" : "", "syncSourceId" : -1, "infoMessage" : "", "electionTime" : Timestamp(1603337640, 1), "electionDate" : ISODate("2020-10-22T03:34:00Z"), "configVersion" : 1, "configTerm" : 2, "self" : true, "lastHeartbeatMessage" : "" }, { "_id" : 2, "name" : "192.168.130.128:27019", "health" : 1, "state" : 2, "stateStr" : "SECONDARY", "uptime" : 174, "optime" : { "ts" : Timestamp(1603337761, 1), "t" : NumberLong(2) }, "optimeDurable" : { "ts" : Timestamp(1603337761, 1), "t" : NumberLong(2) }, "optimeDate" : ISODate("2020-10-22T03:36:01Z"), "optimeDurableDate" : ISODate("2020-10-22T03:36:01Z"), "lastHeartbeat" : ISODate("2020-10-22T03:36:09.922Z"), "lastHeartbeatRecv" : ISODate("2020-10-22T03:36:10.907Z"), "pingMs" : NumberLong(0), "lastHeartbeatMessage" : "", "syncSourceHost" : "192.168.130.128:27018", "syncSourceId" : 1, "infoMessage" : "", "configVersion" : 1, "configTerm" : 2 } ], "ok" : 1, "$clusterTime" : { "clusterTime" : Timestamp(1603337761, 1), "signature" : { "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId" : NumberLong(0) } }, "operationTime" : Timestamp(1603337761, 1) }停止集群中的2个节点 当前集群无法选举出Priamry，无法提供写操作，只能进行读操作 此时已经只有两个节点（一主一从） 我们停止主节点
docker stop mongo02进入mongo03容器
docker exec -it mongo03 /bin/bash mongo可以看到节点三仍然是从节点。
增加arbiter节点 当集群中的节点数为偶数时，如一主一从情况下，任意一节点宕机都无法选举出Priamry，无法提供写操作，加入 arbiter节点后即可解决该问题。 我们开启mongo02，mongo01容器
docker start mongo02此时为一主两从 创建一个新的容器作为arbiter节点
docker create --name mongo04 -p 27020:27017 -v mongo-data-04:/data/db mongo -replSet "rs0" --bind_ip_all docker start mongo04在主节点移除一个节点
rs.remove("192.168.130.128:27017")响应
{ "ok" : 1, "$clusterTime" : { "clusterTime" : Timestamp(1603338733, 1), "signature" : { "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId" : NumberLong(0) } }, "operationTime" : Timestamp(1603338733, 1) }ps:添加节点
rs.add("192.168.130.128:27017");此时为一主一从（mongo03为主节点） 加入arbiter节点
rs.addArb("192.168.130.128:27020")响应
{ "ok" : 1, "$clusterTime" : { "clusterTime" : Timestamp(1603338259, 1), "signature" : { "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId" : NumberLong(0) } }, "operationTime" : Timestamp(1603338259, 1) }此时停止主节点(mongo03)
docker stop mongo03进入mongo02
docker exec -it mongo02 /bin/bash mongo已成为主节点
