MongoDB复制集的选举原理详解以及复制集管理简介

前言介绍

复制的原理：

复制操作是基于oplog，类似mysql中的bin-log，只记录发生改变的记录。

选举的原理：

节点分为：标准节点、被动节点和仲裁节点。

• 标准节点（priority值高）：只有标准节点才可成为primary；

• 被动节点（priority值低）：被动节点只能是secondary；

• 仲裁节点：不能复制数据、不可成为活跃点、只有选举权；

选举结果：票数高者获胜；若票数相同，数据新者获胜

一、复制集选举实验介绍

实验步骤

1. 查看oplog日志

2. 配置复制集的优先级

3. 模拟主节点故障

4. 模拟所有标准节点故障

二、复制集选举实验内容

---------------------------查看oplog日志-------------------------

> use schoolswitched to db school> db.info.insert({"id":1,"name":"tom"})WriteResult({ "nInserted" : 1 })> db.info.find(){ "_id" : ObjectId("5b9a0873692de658bd931c64"), "id" : 1, "name" : "tom" }> use localswitched to db local> show collectionsmeoplog.rs…> db.oplog.rs.find()                { "ts" : Timestamp(1536723445, 3), … : { "create" : "transactions", "idIndex" : { "v" : 2, "key" : { "_id" : 1 }, "name" : "_id_", "ns" : "config.transactions" } } }{ "ts" : Timestamp(1536723445, 5), …: { "create" : "system.keys", "idIndex" : { "v" : 2, "key" : { "_id" : 1 }, "name" : "_id_", "ns" : "admin.system.keys" } } }

------------------------配置复制集的优先级----------------------------

cfg={"_id":"yandada","members": [{"_id":0,"host":"192.168.218.149:27017","priority":100},{"_id":1,"host":"192.168.218.149:27018","priority":100},{"_id":2,"host":"192.168.218.149:27019","priority":0},{"_id":3,"host":"192.168.218.149:27020","arbiterOnly":true}]}

rs.reconfig(cfg)

{ "ok" : 1 } //显示OK:1时表示节点配置成功

rs.status() //查看状态信息

rs.isMaster() //查看节点信息

{ //显示信息如下
"hosts" : [
"192.168.218.149:27017",
"192.168.218.149:27018"
],
"passives" : [
"192.168.218.149:27019"
],
"arbiters" : [
"192.168.218.149:27020"
]

------------------------模拟主节点故障----------------------------

关闭主节点服务器

yandada:PRIMARY> use admin #进入admin集合才能进行下一步操作
switched to db admin
yandada:PRIMARY> db.shutdownServer() #关闭服务器
server should be down…

以上操作等同于[root@yandada3 ~]# mongod -f /etc/mongod.conf --shutdown

[root@yandada3 ~]# mongo --port 27018

yandada:PRIMARY> rs.status()

查看状态信息后会发现MongoDB复制集会选举第二个标准节点作为主节点

---------------------------模拟所有标准节点故障------------------------

[root@yandada3 ~]# mongod -f /etc/mongod.conf --shutdown
killing process with pid: 4238

[root@yandada3 ~]# mongo --port 27019

yandada:SECONDARY> rs.status()

查看查看状态信息后会发现无primary节点，被动节点无法成为主节点

三、复制集管理简介

1.配置允许从节点读取数据

yandada:SECONDARY> rs.slaveOk()

2.查看复制集状态信息

rs.help()

yandada:PRIMARY> rs.printReplicationInfo()
configured oplog size: 990MB #oplog存储大小为990MB
log length start to end: 101403secs (28.17hrs)
oplog first event time: Wed Sep 12 2018 11:37:13 GMT+0800 (CST)
oplog last event time: Thu Sep 13 2018 15:47:16 GMT+0800 (CST)
now: Thu Sep 13 2018 15:47:17 GMT+0800 (CST)
yandada:PRIMARY> rs.printSlaveReplicationInfo()
source: 192.168.218.149:27018
syncedTo: Thu Sep 13 2018 15:47:26 GMT+0800 (CST)
0 secs (0 hrs) behind the primary
source: 192.168.218.149:27019
syncedTo: Thu Sep 13 2018 15:47:26 GMT+0800 (CST)
0 secs (0 hrs) behind the primary

3.更改oplog大小

1.第一步，退出复制集

yandada:PRIMARY> use admin
switched to db admin
yandada:PRIMARY> db.shutdownServer()
server should be down…

2.第二步，更改端口(复制集中含有源端口)，关闭配置文件中复制集名称，启动mongod

vim /etc/mongod.conf

net:
port: 2

#replication:
# replSetName: yandada

mongod -f /etc/mongod.conf

3.第三步，更改oplog大小

[root@yandada3 ~]# mongo --port 27028

> use local
switched to db local
> db.oplog.rs.drop()
true
> db.runCommand({create:"oplog.rs",capped:true,size:(2*2048*2048*2048)})
{ "ok" : 1 }

[root@yandada3 ~]# mongod -f /etc/mongod.conf --shutdown
killing process with pid: 8296
[root@yandada3 ~]# vim /etc/mongod.conf

net:
port: 27017

replication:
replSetName: yandada
oplogSizeMB: 16384

[root@yandada3 ~]# mongod -f /etc/mongod.conf

[root@yandada3 ~]# mongo

yandada:SECONDARY> rs.printReplicationInfo()

configured oplog size: 16384MB #oplog大小更改为16G

4.认证部署

1.第一步，创建认证用户

yandada:PRIMARY> use admin
switched to db admin
yandada:PRIMARY> db.createUser({"user":"root","pwd":"123","roles":["root"]})
Successfully added user: { "user" : "root", "roles" : [ "root" ] }

2.第二步，编辑认证配置

vim /etc/mongod.conf

security:

keyFile: /usr/bin/kgcrskey1

clusterAuthMode:keyFile 注：需要与上一行齐平

同理，修改mongod[2,3,4]文件

[root@yandada3 ~]# echo "kgcrs key" > /usr/bin/kgcrskey[1,2,3,4]

[root@yandada3 bin]# echo "kgcrs key" > /usr/bin/kgcrskey1
[root@yandada3 bin]# echo "kgcrs key" > /usr/bin/kgcrskey2
[root@yandada3 bin]# echo "kgcrs key" > /usr/bin/kgcrskey3
[root@yandada3 bin]# echo "kgcrs key" > /usr/bin/kgcrskey4

[root@yandada3 bin]# chmod 600 /usr/bin/kgcrskey{1,2,3,4}

3.第三步，重启服务

[root@yandada3 bin]# mongod -f /etc/mongod.conf --shutdown

[root@yandada3 bin]# mongod -f /etc/mongod.conf

同理，重启mongod[2,3,4]

4.第四步，查看配置状况

yandada:PRIMARY> show dbs

"ok" : 0 #无权查看

yandada:PRIMARY> use admin
switched to db admin
yandada:PRIMARY> db.auth("root","123")
1 #返回值为1，表示授权成功
yandada:PRIMARY> show dbs
admin 0.000GB
config 0.000GB
local 0.000GB
school 0.000GB