MongoDB提供两种复制风格：主从复制、副本集
- 两种方式都是在一个主节点进行写操作（写入的数据被异步地同步到所有的从节点），并从节点上读取数据。
- 副本集保证自动故障转移，如果主节点由于某种原因下线，可能的花，会自动将一哥从节点提升为主节点。
- 只有一种情况需要选择MongoDB的主从复制，即需要超过11个从节点时，因为副本集不能包含12个以上的成员。
为副本集的每个成员创建数据目录：
[root@vhost2 ~]# mkdir -p /data/mongo1[root@vhost2 ~]# mkdir -p /data/mongo2[root@vhost2 ~]# mkdir -p /data/mongo3启动mongod[root@vhost2 ~]# mongod --replSet myapp --dbpath /data/mongo1 --port 40001 &[root@vhost2 ~]# mongod --replSet myapp --dbpath /data/mongo2 --port 40002 &[root@vhost2 ~]# mongod --replSet myapp --dbpath /data/mongo3 --port 40003 &配置副本集，先连接到一个刚启动的非冲裁节点的mongod上,[root@vhost2 ~]# mongo 127.0.0.1:40001/adminMongoDB Enterprise > rs.initiate()
{ "info2" : "no configuration specified. Using a default configuration for the set", "me" : "vhost2:40001", "ok" : 1}MongoDB Enterprise myapp:OTHER> 1分钟之后，配置了拥有一个单成员的副本集，通过rs.add()添加其他两个成员：MongoDB Enterprise myapp:PRIMARY> rs.add("vhost2:40002"){ "ok" : 1 }MongoDB Enterprise myapp:PRIMARY> rs.add("vhost2.local:40003",{arbiterOnly:true}){ "ok" : 1 }#arbiterOnly,创建仲裁节点，1分钟之后，所有成员都在线db.isMaster():获取副本集状态的摘要信息MongoDB Enterprise myapp:PRIMARY> db.isMaster()
{ "hosts" : [ "vhost2:40001", "vhost2:40002" ], "arbiters" : [ "vhost2:40003" ], "setName" : "myapp", "setVersion" : 5, "ismaster" : true, "secondary" : false, "primary" : "vhost2:40001", "me" : "vhost2:40001", "electionId" : ObjectId("7fffffff0000000000000001"), "lastWrite" : { "opTime" : { "ts" : Timestamp(1512824958, 1), "t" : NumberLong(1) }, "lastWriteDate" : ISODate("2017-12-09T13:09:18Z") }, "maxBsonObjectSize" : 16777216, "maxMessageSizeBytes" : 48000000, "maxWriteBatchSize" : 1000, "localTime" : ISODate("2017-12-09T13:09:24.062Z"), "maxWireVersion" : 5, "minWireVersion" : 0, "readOnly" : false, "ok" : 1} #rs.status()提供详细的系统信息，除非MongoDB数据库中包含数据量比较大，否则副本集能在30s内上线，在此期间，每个节点的
statStr字段应该会从RECOVERING变为PRIMARY,SECONDARY或ARBITER。MongoDB Enterprise myapp:PRIMARY> rs.status() { "set" : "myapp", "date" : ISODate("2017-12-09T13:08:41.030Z"), "myState" : 1, "term" : NumberLong(1), "heartbeatIntervalMillis" : NumberLong(2000), "optimes" : { "lastCommittedOpTime" : { "ts" : Timestamp(1512824918, 1), "t" : NumberLong(1) }, "appliedOpTime" : { "ts" : Timestamp(1512824918, 1), "t" : NumberLong(1) }, "durableOpTime" : { "ts" : Timestamp(1512824918, 1), "t" : NumberLong(1) } }, "members" : [ { "_id" : 0, "name" : "vhost2:40001", "health" : 1, "state" : 1, "stateStr" : "PRIMARY", "uptime" : 4026, "optime" : { "ts" : Timestamp(1512824918, 1), "t" : NumberLong(1) }, "optimeDate" : ISODate("2017-12-09T13:08:38Z"), "electionTime" : Timestamp(1512820966, 2), "electionDate" : ISODate("2017-12-09T12:02:46Z"), "configVersion" : 5, "self" : true }, { "_id" : 1, "name" : "vhost2:40002", "health" : 1, "state" : 2, "stateStr" : "SECONDARY", "uptime" : 3501, "optime" : { "ts" : Timestamp(1512824918, 1), "t" : NumberLong(1) }, "optimeDurable" : { "ts" : Timestamp(1512824918, 1), "t" : NumberLong(1) }, "optimeDate" : ISODate("2017-12-09T13:08:38Z"), "optimeDurableDate" : ISODate("2017-12-09T13:08:38Z"), "lastHeartbeat" : ISODate("2017-12-09T13:08:39.445Z"), "lastHeartbeatRecv" : ISODate("2017-12-09T13:08:40.483Z"), "pingMs" : NumberLong(0), "syncingTo" : "vhost2:40001", "configVersion" : 5 }, { "_id" : 2, "name" : "vhost2:40003", "health" : 1, "state" : 7, "stateStr" : "ARBITER", "uptime" : 2942, "lastHeartbeat" : ISODate("2017-12-09T13:08:40.900Z"), "lastHeartbeatRecv" : ISODate("2017-12-09T13:08:39.725Z"), "pingMs" : NumberLong(0), "configVersion" : 5 } ], "ok" : 1} MongoDB Enterprise myapp:PRIMARY>
主节点插入数据[root@vhost2 ~]# mongo vhost2:40001/adminMongoDB Enterprise myapp:PRIMARY> use bookstore;switched to db bookstoreMongoDB Enterprise myapp:PRIMARY> db.books.insert({title:"Oliver Twist"})WriteResult({ "nInserted" : 1 })MongoDB Enterprise myapp:PRIMARY> show dbs;admin 0.000GBbookstore 0.000GBlocal 0.000GBMongoDB Enterprise myapp:PRIMARY> db.books.find(){ "_id" : ObjectId("5a2be17a65e2395a10373f77"), "title" : "Oliver Twist" }从节点：[root@vhost2 ~]# mongo vhost2:40002MongoDB Enterprise myapp:SECONDARY> show dbs;2017-12-09T08:16:59.482-0500 E QUERY [thread1] Error: listDatabases failed:{ "ok" : 0, "errmsg" : "not master and slaveOk=false", "code" : 13435, "codeName" : "NotMasterNoSlaveOk"} :_getErrorWithCode@src/mongo/shell/utils.js:25:13Mongo.prototype.getDBs@src/mongo/shell/mongo.js:62:1shellHelper.show@src/mongo/shell/utils.js:781:19shellHelper@src/mongo/shell/utils.js:671:15@(shellhelp2):1:1MongoDB Enterprise myapp:SECONDARY>SECONDARY是不允许读写的，如果非要解决，方法如下：rs.slaveOk();MongoDB Enterprise myapp:SECONDARY> rs.slaveOk();MongoDB Enterprise myapp:SECONDARY> show dbs;admin 0.000GBbookstore 0.000GBlocal 0.000GBMongoDB Enterprise myapp:SECONDARY> use bookstoreswitched to db bookstoreMongoDB Enterprise myapp:SECONDARY> db.books.find(){ "_id" : ObjectId("5a2be17a65e2395a10373f77"), "title" : "Oliver Twist" }冲裁节点：[root@vhost2 ~]# mongo vhost2:40003MongoDB Enterprise myapp:ARBITER> rs.slaveOk();MongoDB Enterprise myapp:ARBITER> show dbs;local 0.000GB切换：关闭主节点，CTRL-C、kill -2 或在SHELL中运行db.shutdownServer()[root@vhost2 ~]# kill -2 26036[root@vhost2 ~]# mongo vhost2:40002MongoDB Enterprise myapp:PRIMARY> show dbs;admin 0.000GBbookstore 0.000GBlocal 0.000GBMongoDB Enterprise myapp:PRIMARY> rs.status() { "set" : "myapp", "date" : ISODate("2017-12-09T14:22:06.153Z"), "myState" : 1, "term" : NumberLong(2), "heartbeatIntervalMillis" : NumberLong(2000), "optimes" : { "lastCommittedOpTime" : { "ts" : Timestamp(1512829209, 1), "t" : NumberLong(1) }, "appliedOpTime" : { "ts" : Timestamp(1512829322, 1), "t" : NumberLong(2) }, "durableOpTime" : { "ts" : Timestamp(1512829322, 1), "t" : NumberLong(2) } }, "members" : [ { "_id" : 0, "name" : "vhost2:40001", "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("2017-12-09T14:22:04.668Z"), "lastHeartbeatRecv" : ISODate("2017-12-09T14:20:08.573Z"), "pingMs" : NumberLong(0), "lastHeartbeatMessage" : "Connection refused", "configVersion" : -1 }, { "_id" : 1, "name" : "vhost2:40002", "health" : 1, "state" : 1, "stateStr" : "PRIMARY", "uptime" : 8409, "optime" : { "ts" : Timestamp(1512829322, 1), "t" : NumberLong(2) }, "optimeDate" : ISODate("2017-12-09T14:22:02Z"), "infoMessage" : "could not find member to sync from", "electionTime" : Timestamp(1512829220, 1), "electionDate" : ISODate("2017-12-09T14:20:20Z"), "configVersion" : 5, "self" : true }, { "_id" : 2, "name" : "vhost2:40003", "health" : 1, "state" : 7, "stateStr" : "ARBITER", "uptime" : 7304, "lastHeartbeat" : ISODate("2017-12-09T14:22:04.428Z"), "lastHeartbeatRecv" : ISODate("2017-12-09T14:22:05.986Z"), "pingMs" : NumberLong(0), "configVersion" : 5 } ], "ok" : 1}MongoDB Enterprise myapp:PRIMARY> 故障转移后，副本集就只有两个节点，仲裁节点没有数据。假设旧的主节点正常关闭，启动该节点，
它将以从节点的身份重新键入副本集：重启主节点：[root@vhost2 ~]# mongo vhost2:40001/adminMongoDB Enterprise myapp:SECONDARY> show dbs;2017-12-09T09:24:34.262-0500 E QUERY [thread1] Error: listDatabases failed:{ "ok" : 0, "errmsg" : "not master and slaveOk=false", "code" : 13435, "codeName" : "NotMasterNoSlaveOk"} :_getErrorWithCode@src/mongo/shell/utils.js:25:13Mongo.prototype.getDBs@src/mongo/shell/mongo.js:62:1shellHelper.show@src/mongo/shell/utils.js:781:19shellHelper@src/mongo/shell/utils.js:671:15@(shellhelp2):1:1MongoDB Enterprise myapp:SECONDARY> rs.slaveOk()MongoDB Enterprise myapp:SECONDARY> show dbs;admin 0.000GBbookstore 0.000GBlocal 0.000GBMongoDB Enterprise myapp:SECONDARY> rs.strs.status( rs.stepDown(MongoDB Enterprise myapp:SECONDARY> rs.status(){ "set" : "myapp", "date" : ISODate("2017-12-09T14:24:47.063Z"), "myState" : 2, "term" : NumberLong(2), "syncingTo" : "vhost2:40002", "heartbeatIntervalMillis" : NumberLong(2000), "optimes" : { "lastCommittedOpTime" : { "ts" : Timestamp(1512829482, 1), "t" : NumberLong(2) }, "appliedOpTime" : { "ts" : Timestamp(1512829482, 1), "t" : NumberLong(2) }, "durableOpTime" : { "ts" : Timestamp(1512829482, 1), "t" : NumberLong(2) } }, "members" : [ { "_id" : 0, "name" : "vhost2:40001", "health" : 1, "state" : 2, "stateStr" : "SECONDARY", "uptime" : 77, "optime" : { "ts" : Timestamp(1512829482, 1), "t" : NumberLong(2) }, "optimeDate" : ISODate("2017-12-09T14:24:42Z"), "syncingTo" : "vhost2:40002", "configVersion" : 5, "self" : true }, { "_id" : 1, "name" : "vhost2:40002", "health" : 1, "state" : 1, "stateStr" : "PRIMARY", "uptime" : 63, "optime" : { "ts" : Timestamp(1512829482, 1), "t" : NumberLong(2) }, "optimeDurable" : { "ts" : Timestamp(1512829482, 1), "t" : NumberLong(2) }, "optimeDate" : ISODate("2017-12-09T14:24:42Z"), "optimeDurableDate" : ISODate("2017-12-09T14:24:42Z"), "lastHeartbeat" : ISODate("2017-12-09T14:24:45.594Z"), "lastHeartbeatRecv" : ISODate("2017-12-09T14:24:47.010Z"), "pingMs" : NumberLong(0), "electionTime" : Timestamp(1512829220, 1), "electionDate" : ISODate("2017-12-09T14:20:20Z"), "configVersion" : 5 }, { "_id" : 2, "name" : "vhost2:40003", "health" : 1, "state" : 7, "stateStr" : "ARBITER", "uptime" : 63, "lastHeartbeat" : ISODate("2017-12-09T14:24:45.598Z"), "lastHeartbeatRecv" : ISODate("2017-12-09T14:24:46.216Z"), "pingMs" : NumberLong(0), "configVersion" : 5 } ], "ok" : 1}MongoDB Enterprise myapp:SECONDARY>