MongoDB复制集——如何将单节点转换成复制集

具体步骤如下：

1. 停止单节点的mongod

我们可以从mongo shell里运行db.shutdownServer()命令来停止mongod

[javascript] 
> use admin;  
switched to db admin  
> db.shutdownServer()

2. 使用--replSet的选项加上新的复制集的名字来重新启动这个mongod

[javascript] 
bash-3.2$ mongod --dbpath /data/db --logpath /data/mongod.log --logappend --fork --port 30000 --replSet rs0  
about to fork child process, waiting until server is ready for connections.  
forked process: 3092  
all output going to: /data/mongod.log  
child process started successfully, parent exiting

3. 连接刚才启动的数据库

[javascript] 
bash-3.2$ mongo --port 30000  
MongoDB shell version: 2.4.5  
connecting to: 127.0.0.1:30000/test  
Server has startup warnings:   
Mon Jul 29 11:28:02.291 [initandlisten]   
Mon Jul 29 11:28:02.291 [initandlisten] ** WARNING: soft rlimits too low. Number of files is 256, should be at least 1000

4. 在mongo shell里创建一个包含复制集配置信息的对象

[javascript] 
rsconf = {  
           _id: "rs0",  
           members: [  
                      {  
                       _id: 0,  
                       host: "localhost:30000"  
                      }  
                    ]  
         }

5. 用rs.initiate()来初始化复制集

[javascript] 
> rs.initiate( rsconf )  
{  
    "info" : "Config now saved locally.  Should come online in about a minute.",  
    "ok" : 1  
}

6. 初始化完毕后，我们可以用rs.conf()来查看复制集的配置

[javascript] 
> rs.conf()  
{  
    "_id" : "rs0",  
    "version" : 1,  
    "members" : [  
        {  
            "_id" : 0,  
            "host" : "localhost:30000"  
        }  
    ]  
}

7. 我们还可以用rs.status()来查看复制集的运行状态

[javascript] 
rs0:PRIMARY> rs.status()  
{  
    "set" : "rs0",  
    "date" : ISODate("2013-07-29T02:15:07Z"),  
    "myState" : 1,  
    "members" : [  
        {  
            "_id" : 0,  
            "name" : "localhost:30000",  
            "health" : 1,  
            "state" : 1,  
            "stateStr" : "PRIMARY",  
            "uptime" : 2185,  
            "optime" : Timestamp(1375062044, 1),  
            "optimeDate" : ISODate("2013-07-29T01:40:44Z"),  
            "self" : true  
        }  
    ],  
    "ok" : 1  
}

8. 启动一个新的mongod服务

[javascript] 
bash-3.2$ mkdir -p /data/db2  
bash-3.2$ mongod --dbpath /data/db2 --logpath /data/db2/mongod.log --logappend --fork --port 30001 --replSet rs0  
about to fork child process, waiting until server is ready for connections.  
forked process: 3118  
all output going to: /data/db2/mongod.log  
child process started successfully, parent exiting

9. 将新的mongod添加到复制集里

[javascript] 
rs0:PRIMARY> rs.add("localhost:30001")  
{ "ok" : 1 }

10. 再启动一个新的mongod服务来作为仲裁节点

[javascript] 
bash-3.2$ mkdir -p /data/arb  
bash-3.2$ mongod --dbpath /data/arb --logpath /data/arb/mongod.log --logappend --fork --port 30002 --replSet rs0  
about to fork child process, waiting until server is ready for connections.  
forked process: 3124  
all output going to: /data/arb/mongod.log  
child process started successfully, parent exiting

11. 将新启动的mongod服务作为仲裁节点添加到复制集中

[javascript] 
rs0:PRIMARY> rs.addArb("localhost:30002")  
{ "ok" : 1 }

12. 查看复制集的状态

[javascript] 
rs0:PRIMARY> rs.status()  
{  
    "set" : "rs0",  
    "date" : ISODate("2013-07-29T02:18:20Z"),  
    "myState" : 1,  
    "members" : [  
        {  
            "_id" : 0,  
            "name" : "localhost:30000",  
            "health" : 1,  
            "state" : 1,  
            "stateStr" : "PRIMARY",  
            "uptime" : 2378,  
            "optime" : Timestamp(1375064276, 1),  
            "optimeDate" : ISODate("2013-07-29T02:17:56Z"),  
            "self" : true  
        },  
        {  
            "_id" : 1,  
            "name" : "localhost:30001",  
            "health" : 1,  
            "state" : 2,  
            "stateStr" : "SECONDARY",  
            "uptime" : 34,  
            "optime" : Timestamp(1375064276, 1),  
            "optimeDate" : ISODate("2013-07-29T02:17:56Z"),  
            "lastHeartbeat" : ISODate("2013-07-29T02:18:18Z"),  
            "lastHeartbeatRecv" : ISODate("2013-07-29T02:18:18Z"),  
            "pingMs" : 0,  
            "syncingTo" : "localhost:30000"  
        },  
        {  
            "_id" : 2,  
            "name" : "localhost:30002",  
            "health" : 1,  
            "state" : 7,  
            "stateStr" : "ARBITER",  
            "uptime" : 24,  
            "lastHeartbeat" : ISODate("2013-07-29T02:18:18Z"),  
            "lastHeartbeatRecv" : ISODate("2013-07-29T02:18:19Z"),  
            "pingMs" : 0  
        }  
    ],  
    "ok" : 1  
}

从上面的步骤我们可以看到，只需要先停止单节点的mongod，再用复制集的参数来启动mongod，然后初始化复制集，就可以把一个单节点的mongod转换成含有一个节点的复制集，随后就可以往这个复制集里添加从节点和仲裁节点。有了这么一个复制集的环境，我们就可以开始学习如何管理操作复制集了。