MongoDB復(fù)制原理就是主節(jié)點(diǎn)記錄在其上的所有操作oplog，從節(jié)點(diǎn)定期輪詢主節(jié)點(diǎn)獲取這些操作，然后對(duì)自己的數(shù)據(jù)副本執(zhí)行這些操作，從而保證從節(jié)點(diǎn)的數(shù)據(jù)與主節(jié)點(diǎn)一致。
那什么是副本集呢？主從模式一主一從就是一個(gè)副本。MongoDB復(fù)制提供了數(shù)據(jù)的冗余備份，并在多個(gè)服務(wù)器上存儲(chǔ)數(shù)據(jù)副本，提高了數(shù)據(jù)的可用性， 并可以保證數(shù)據(jù)的安全性;復(fù)制還允許您從硬件故障和服務(wù)中斷中恢復(fù)數(shù)據(jù)。副本集具有多個(gè)副本保證了容錯(cuò)性，就算一個(gè)副本掛掉了還有很多副本存在，并且解決了之前的問題“主節(jié)點(diǎn)掛掉了，整個(gè)集群內(nèi)會(huì)自動(dòng)切換”。
副本集特征：
· N 個(gè)節(jié)點(diǎn)的集群
· 任何節(jié)點(diǎn)可作為主節(jié)點(diǎn)
· 所有寫入操作都在主節(jié)點(diǎn)上
· 自動(dòng)故障轉(zhuǎn)移
· 自動(dòng)恢復(fù)
副本集還有以下幾個(gè)需要注意的地方：
1. 最小構(gòu)成是：primary，secondary，arbiter，一般部署是：primary，2 secondary。
2. 成員數(shù)應(yīng)該為奇數(shù)，如果為偶數(shù)的情況下添加arbiter，arbiter不保存數(shù)據(jù)，只投票。
3. 最大50 members，但是只能有 7 voting members，其他是non-voting members。
借用網(wǎng)上找的兩張架構(gòu)圖說明一下：
由圖可以看到客戶端連接到整個(gè)副本集，不關(guān)心具體哪一臺(tái)機(jī)器是否掛掉。主服務(wù)器負(fù)責(zé)整個(gè)副本集的讀寫，副本集定期同步數(shù)據(jù)備份，一但主節(jié)點(diǎn)掛掉，副本節(jié)點(diǎn)就會(huì)選舉一個(gè)新的主服務(wù)器，這一切對(duì)于應(yīng)用服務(wù)器不需要關(guān)心。我們看一下主服務(wù)器掛掉后的架構(gòu)：
3. 創(chuàng)建三個(gè)節(jié)點(diǎn)的配置文件
[root@MidApp mongodb]# cat mongodb1.conf
dbpath=/data/db1
logpath=/usr/local/mongodb/logs/mongodb1.log
logappend=true
port=27017
fork=true
auth=false
nohttpinterface=false
bind_ip=192.168.221.161
journal=true
quiet=true
replSet=repset
[root@MidApp mongodb]# cat mongodb2.conf
dbpath=/data/db2
logpath=/usr/local/mongodb/logs/mongodb2.log
logappend=true
port=27018
fork=true
auth=false
nohttpinterface=false
bind_ip=192.168.221.161
journal=true
quiet=true
replSet=repset
[root@MidApp mongodb]# cat mongodb3.conf
dbpath=/data/db3
logpath=/usr/local/mongodb/logs/mongodb3.log
logappend=true
port=27019
fork=true
auth=false
nohttpinterface=false
bind_ip=192.168.221.161
journal=true
quiet=true
replSet=repset
4. 分別啟動(dòng)三個(gè)節(jié)點(diǎn)
mongod -f mongodb1.conf
mongod -f mongodb2.conf
mongod -f mongodb3.conf
查看日志輸出，沒有找到replica的配置信息
2017-11-13T16:34:46.212-0800 I CONTROL [initandlisten] options: { config: "mongodb1.conf", net: { bindIp: "192.168.221.160", http: { enabled: true }, port: 27017 }, processManagement: { fork: true }, replication: { replSet: "repset" }, security: { authorization: "disabled" }, storage: { dbPath: "/data/db1", journal: { enabled: true } }, systemLog: { destination: "file", logAppend: true, path: "/usr/local/mongodb/logs/mongodb1.log", quiet: true } }
2017-11-13T16:34:46.214-0800 I INDEX [initandlisten] allocating new ns file /data/db1/local.ns, filling with zeroes...
2017-11-13T16:34:46.216-0800 I JOURNAL [journal writer] Journal writer thread started
2017-11-13T16:34:46.492-0800 I STORAGE [FileAllocator] allocating new datafile /data/db1/local.0, filling with zeroes...
2017-11-13T16:34:46.492-0800 I STORAGE [FileAllocator] creating directory /data/db1/_tmp
2017-11-13T16:34:46.501-0800 I STORAGE [FileAllocator] done allocating datafile /data/db1/local.0, size: 64MB, took 0.001 secs
2017-11-13T16:34:46.520-0800 I REPL [initandlisten] Did not find local replica set configuration document at startup; NoMatchingDocument Did not find replica set configuration document in local.system.replset
5. 初始化副本集
任選一個(gè)節(jié)點(diǎn)登錄進(jìn)去，可以看到show dbs是不可用，因?yàn)檫€沒初始化副本集
[root@MidApp mongodb]# mongo 192.168.221.161
MongoDB shell version: 3.0.6
connecting to: 192.168.221.161/test
Welcome to the MongoDB shell.
For interactive help, type "help".
For more comprehensive documentation, see
http://docs.mongodb.org/
Questions? Try the support group
http://groups.google.com/group/mongodb-user
> show dbs
2017-11-13T16:39:33.235-0800 E QUERY Error: listDatabases failed:{ "note" : "from execCommand", "ok" : 0, "errmsg" : "not master" }
at Error (<anonymous>)
at Mongo.getDBs (src/mongo/shell/mongo.js:47:15)
at shellHelper.show (src/mongo/shell/utils.js:630:33)
at shellHelper (src/mongo/shell/utils.js:524:36)
at (shellhelp2):1:1 at src/mongo/shell/mongo.js:47
> use admin
switched to db admin
定義副本集配置變量，這里的 _id:”repset” 和上面配置文件的參數(shù)“ –replSet repset” 要保持一樣
>config= {_id:"repset",members:[
{_id:0,host:"192.168.221.161:27017"},
{_id:1,host:"192.168.221.161:27018"},
{_id:2,host:"192.168.221.161:27019"}]
}
查看輸出信息：
{
"_id" : "repset",
"members" : [
{
"_id" : 0,
"host" : "192.168.221.161:27017"
},
{
"_id" : 1,
"host" : "192.168.221.161:27018"
},
{
"_id" : 2,
"host" : "192.168.221.161:27019"
}
]
}
初始化副本集配置
12 > rs.initiate(config);
{ "ok" : 1 }
查看集群節(jié)點(diǎn)狀態(tài)：
repset:OTHER> rs.status()
{
"set" : "repset",
"date" : ISODate("2017-11-14T00:49:25.782Z"),
"myState" : 1,
"members" : [
{
"_id" : 0,
"name" : "192.168.221.161:27017",
"health" : 1,
"state" : 1,
"stateStr" : "PRIMARY",
"uptime" : 695,
"optime" : Timestamp(1510620540, 1),
"optimeDate" : ISODate("2017-11-14T00:49:00Z"),
"electionTime" : Timestamp(1510620544, 1),
"electionDate" : ISODate("2017-11-14T00:49:04Z"),
"configVersion" : 1,
"self" : true
},
{
"_id" : 1,
"name" : "192.168.221.161:27018",
"health" : 1,
"state" : 2,
"stateStr" : "SECONDARY",
"uptime" : 25,
"optime" : Timestamp(1510620540, 1),
"optimeDate" : ISODate("2017-11-14T00:49:00Z"),
"lastHeartbeat" : ISODate("2017-11-14T00:49:24.739Z"),
"lastHeartbeatRecv" : ISODate("2017-11-14T00:49:24.762Z"),
"pingMs" : 0,
"configVersion" : 1
},
{
"_id" : 2,
"name" : "192.168.221.161:27019",
"health" : 1,
"state" : 2,
"stateStr" : "SECONDARY",
"uptime" : 25,
"optime" : Timestamp(1510620540, 1),
"optimeDate" : ISODate("2017-11-14T00:49:00Z"),
"lastHeartbeat" : ISODate("2017-11-14T00:49:24.739Z"),
"lastHeartbeatRecv" : ISODate("2017-11-14T00:49:24.762Z"),
"pingMs" : 0,
"configVersion" : 1
}
],
"ok" : 1
}
整個(gè)副本及已經(jīng)搭建成功了！
6. 測(cè)試副本集數(shù)據(jù)復(fù)制功能
在主節(jié)點(diǎn)登錄mongodb
[root@MidApp mongodb]# mongo 192.168.221.161:27017
MongoDB shell version: 3.0.6
connecting to: 192.168.221.161:27017/test
repset:PRIMARY> use test;
switched to db test
repset:PRIMARY> db.testdb.insert({"test1":"item1"})
WriteResult({ "nInserted" : 1 })
repset:PRIMARY> exit
bye
在副本節(jié)點(diǎn)登錄查看數(shù)據(jù)：
[root@MidApp logs]# mongo 192.168.221.161:27018
MongoDB shell version: 3.0.6
connecting to: 192.168.221.161:27018/test
repset:SECONDARY> use test
switched to db test
repset:SECONDARY> db.getMongo().setSlaveOk();#mongodb默認(rèn)是從主節(jié)點(diǎn)讀寫數(shù)據(jù)的，副本節(jié)點(diǎn)上不允許讀，需要設(shè)置副本節(jié)點(diǎn)可以讀
repset:SECONDARY> db.testdb.find()
{ "_id" : ObjectId("5a0a3e8d40637405ab003b39"), "test1" : "item1" }
7. 測(cè)試副本集failover功能
手動(dòng)把現(xiàn)在的主節(jié)點(diǎn)停掉，查看集群狀態(tài)：
repset:SECONDARY> rs.status()
{
"set" : "repset",
"date" : ISODate("2017-11-14T00:57:14.753Z"),
"myState" : 2,
"members" : [
{
"_id" : 0,
"name" : "192.168.221.161:27017",
"health" : 0,
"state" : 8,
"stateStr" : "(not reachable/healthy)",
"uptime" : 0,
"optime" : Timestamp(0, 0),
"optimeDate" : ISODate("1970-01-01T00:00:00Z"),
"lastHeartbeat" : ISODate("2017-11-14T00:57:13.304Z"),
"lastHeartbeatRecv" : ISODate("2017-11-14T00:57:09.285Z"),
"pingMs" : 0,
"lastHeartbeatMessage" : "Failed attempt to connect to 192.168.221.161:27017; couldn't connect to server 192.168.221.161:27017 (192.168.221.161), connection attempt failed",
"configVersion" : -1
},
{
"_id" : 1,
"name" : "192.168.221.161:27018",
"health" : 1,
"state" : 2,
"stateStr" : "SECONDARY",
"uptime" : 1167,
"optime" : Timestamp(1510620813, 2),
"optimeDate" : ISODate("2017-11-14T00:53:33Z"),
"infoMessage" : "could not find member to sync from",
"configVersion" : 1,
"self" : true
},
{
"_id" : 2,
"name" : "192.168.221.161:27019",
"health" : 1,
"state" : 1,
"stateStr" : "PRIMARY",
"uptime" : 17,
"optime" : Timestamp(1510620813, 2),
"optimeDate" : ISODate("2017-11-14T00:53:33Z"),
"lastHeartbeat" : ISODate("2017-11-14T00:57:13.317Z"),
"lastHeartbeatRecv" : ISODate("2017-11-14T00:57:13.330Z"),
"pingMs" : 0,
"electionTime" : Timestamp(1510621032, 1),
"electionDate" : ISODate("2017-11-14T00:57:12Z"),
"configVersion" : 1
}
],
"ok" : 1
}
可以看到原來(lái)的主節(jié)點(diǎn)狀態(tài)現(xiàn)在已經(jīng)變成了不可達(dá)，192.168.221.161:27019已經(jīng)變成新的主節(jié)點(diǎn)
8. 再次啟動(dòng)原來(lái)的主節(jié)點(diǎn)，發(fā)現(xiàn)192.168.221.161:27017還是SECONDARY
repset:SECONDARY> rs.status()
{
"set" : "repset",
"date" : ISODate("2017-11-14T17:02:13.837Z"),
"myState" : 2,
"members" : [
{
"_id" : 0,
"name" : "192.168.221.161:27017",
"health" : 1,
"state" : 2,
"stateStr" : "SECONDARY",
"uptime" : 5,
"optime" : Timestamp(1510620813, 2),
"optimeDate" : ISODate("2017-11-14T00:53:33Z"),
"lastHeartbeat" : ISODate("2017-11-14T17:02:12.642Z"),
"lastHeartbeatRecv" : ISODate("2017-11-14T17:02:11.902Z"),
"pingMs" : 0,
"configVersion" : 1
},
{
"_id" : 1,
"name" : "192.168.221.161:27018",
"health" : 1,
"state" : 2,
"stateStr" : "SECONDARY",
"uptime" : 59066,
"optime" : Timestamp(1510620813, 2),
"optimeDate" : ISODate("2017-11-14T00:53:33Z"),
"configVersion" : 1,
"self" : true
},
{
"_id" : 2,
"name" : "192.168.221.161:27019",
"health" : 1,
"state" : 1,
"stateStr" : "PRIMARY",
"uptime" : 57916,
"optime" : Timestamp(1510620813, 2),
"optimeDate" : ISODate("2017-11-14T00:53:33Z"),
"lastHeartbeat" : ISODate("2017-11-14T17:02:12.308Z"),
"lastHeartbeatRecv" : ISODate("2017-11-14T17:02:12.080Z"),
"pingMs" : 0,
"electionTime" : Timestamp(1510621032, 1),
"electionDate" : ISODate("2017-11-14T00:57:12Z"),
"configVersion" : 1
}
],
"ok" : 1
}
現(xiàn)在，mongodb的副本集群已經(jīng)完成了。
接下來(lái)是關(guān)于mongodb的讀寫分離和分片的內(nèi)容
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