方法1 只需要直接将主机的配置信息priority改成比其他节点大即可

过几秒钟，members[0]就变成主库了，原主机就变成备库了。

方法2 把不想成为主库的节点暂时冻结。然后把主库降级。

现有节点：

1 primary

2 secondary

3 secondary

4 arbiter

在2号执行

(冻结200秒，200秒内不能参与投票)

rs0:SECONDARY> rs.freeze(200) { "ok" : 1 }

在1号执行

(主库降级为备库，并且在200秒之内不能参与投票)

rs0:PRIMARY> rs.stepDown(200) 2015-03-18T13:54:46.217+0800 I NETWORK  DBClientCursor::init call() failed 2015-03-18T13:54:46.235+0800 E QUERY    Error: error doing query: failed     at DBQuery._exec (src/mongo/shell/query.js:83:36)     at DBQuery.hasNext (src/mongo/shell/query.js:240:10)     at DBCollection.findOne (src/mongo/shell/collection.js:186:19)     at DB.runCommand (src/mongo/shell/db.js:58:41)     at DB.adminCommand (src/mongo/shell/db.js:66:41)     at Function.rs.stepDown (src/mongo/shell/utils.js:1001:43)     at (shell):1:4 at src/mongo/shell/query.js:83 2015-03-18T13:54:46.237+0800 I NETWORK  trying reconnect to 127.0.0.1:4444 (127.0.0.1) failed 2015-03-18T13:54:46.238+0800 I NETWORK  reconnect 127.0.0.1:4444 (127.0.0.1) ok

3号节点变成主库

rs0:PRIMARY> rs.isMaster() {         "setName" : "rs0",         "setVersion" : 10,         "ismaster" : true,         "secondary" : false,         "hosts" : [                 "db11:4444",                 "1.1.1.101:4001",                 "1.1.1.102:4002"         ],         "arbiters" : [                 "1.1.1.100:4000"         ],         "primary" : "1.1.1.102:4002",         "me" : "1.1.1.102:4002",         "electionId" : ObjectId("550913287121d6dc4a60de08"),         "maxBsonObjectSize" : 16777216,         "maxMessageSizeBytes" : 48000000,         "maxWriteBatchSize" : 1000,         "localTime" : ISODate("2015-03-18T05:55:34.651Z"),         "maxWireVersion" : 3,         "minWireVersion" : 0,         "ok" : 1 }