MongoDB 高可用可用分两种:
Master-Slave 主从复制：：
只需要在某一个服务启动时加上–master 参数，而另一个服务加上–slave 与–source 参数，
即可实现同步。 MongoDB 的最新版本已不再推荐此方案。
Replica Sets 复制集：：
MongoDB 在 1.6 版本对开发了新功能 replica set，这比之前的 replication 功能要强大一
些，增加了故障自动切换和自动修复成员节点，各个 DB 之间数据完全一致，大大降低了维
护成功。 auto shard 已经明确说明不支持 replication paris，建议使用 replica set， replica set
故障切换完全自动。

1、创建数据文件存储路径

[root@localhost ~]# mkdir -p /data/data/r0
[root@localhost ~]# mkdir -p /data/data/r1
[root@localhost ~]# mkdir -p /data/data/r2

2、创建日志文件路径

[root@localhost ~]# mkdir -p /data/log

3、创建主从 key 文件，用于标识集群的私钥的完整路径，如果各个实例的 key file 内容不一
致，程序将不能正常用。

[root@localhost ~]# mkdir -p /data/key
[root@localhost ~]# echo "this is rs1 super secret key" > /data/key/r0
[root@localhost ~]# echo "this is rs1 super secret key" > /data/key/r1
[root@localhost ~]# echo "this is rs1 super secret key" > /data/key/r2
[root@localhost ~]# chmod 600 /data/key/r*

4、启动 3 个实例

[root@localhost ~]# /Apps/mongo/bin/mongod --replSet rs1 --keyFile /data/key/r0 --fork --port
28010 --dbpath /data/data/r0 --logpath=/data/log/r0.log --logappend
all output going to: /data/log/r0.log
forked process: 6573
[root@localhost ~]# /Apps/mongo/bin/mongod --replSet rs1 --keyFile /data/key/r1 --fork --port
28011 --dbpath /data/data/r1 --logpath=/data/log/r1.log --logappend
all output going to: /data/log/r1.log
forked process: 6580
[root@localhost ~]# /Apps/mongo/bin/mongod --replSet rs1 --keyFile /data/key/r2 --fork --port
28012 --dbpath /data/data/r2 --logpath=/data/log/r2.log --logappend
all output going to: /data/log/r2.log
forked process: 6585

5、配置及初始化 Replica Sets

[root@localhost bin]# /Apps/mongo/bin/mongo -port 28010
MongoDB shell version: 1.8.1
connecting to: 127.0.0.1:28010/test
> config_rs1 = {_id: 'rs1', members: [
... {_id: 0, host: 'localhost:28010', priority:1}, --成员 IP 及端口,最好是写ip那样就可以跨机器， priority=1 指 PRIMARY
... {_id: 1, host: 'localhost:28011'},
... {_id: 2, host: 'localhost:28012'}]
... }
{
"_id" : "rs1",
"members" : [
{
"_id" : 0,
"host" : "localhost:28010"
},
{
"_id" : 1,
"host" : "localhost:28011"
},
{
"_id" : 2,
"host" : "localhost:28012"
}
]
}
> rs.initiate(config_rs1); --初始化配置
{
"info" : "Config now saved locally. Should come online in about a minute.",
"ok" : 1
}

6查看复制集状态
> rs.status()

{
"set" : "rs1",
"date" : ISODate("2012-05-31T09:49:57Z"),
"myState" : 1,
"members" : [
{
"_id" : 0,
"name" : "localhost:28010",
"health" : 1, --1 表明正常; 0 表明异常
"state" : 1, -- 1 表明是 Primary; 2 表明是 Secondary;
"stateStr" : "PRIMARY", --表明此机器是主库
"optime" : {
"t" : 1338457763000,
"i" : 1
},
"optimeDate" : ISODate("2012-05-31T09:49:23Z"),
"self" : true
},
{
"_id" : 1,
"name" : "localhost:28011",
"health" : 1,
65 / 91
"state" : 2,
"stateStr" : "SECONDARY",
"uptime" : 23,
"optime" : {
"t" : 1338457763000,
"i" : 1
},
"optimeDate" : ISODate("2012-05-31T09:49:23Z"),
"lastHeartbeat" : ISODate("2012-05-31T09:49:56Z")
},
{
"_id" : 2,
"name" : "localhost:28012",
"health" : 1,
"state" : 2,
"stateStr" : "SECONDARY",
"uptime" : 23,
"optime" : {
"t" : 1338457763000,
"i" : 1
},
"optimeDate" : ISODate("2012-05-31T09:49:23Z"),
"lastHeartbeat" : ISODate("2012-05-31T09:49:56Z")
}
],
"ok" : 1
}

还可以用 isMaster 查看 Replica Sets 状态。

rs1:PRIMARY> rs.isMaster()
{
"setName" : "rs1",
"ismaster" : true,
"secondary" : false,
"hosts" : [
"localhost:28010",
"localhost:28012",
"localhost:28011"
],
"maxBsonObjectSize" : 16777216,
"ok" : 1
}

rs1:PRIMARY>rs.conf()
shard1:SECONDARY> use local
switched to db local
shard1:SECONDARY> db.system.replset.find()

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