如果只有一个节点或者使用Master-Slave模式，存在主机挂掉后“单点失效”的问题。通过使用Mongo DB副本集，可以提高容错性和可用性~~
Areplica setin MongoDB is a group of
mongodprocesses that maintain the same data set. Replica sets provide redundancy and high availability
什么是副本集( Repilca Set )？
副本集在Mongo DB中就是一组mongod维护相同的数据集，副本集提供冗余和高可用~~
一个三个节点的副本集如下图所示：
本篇博文主要给出一个搭建三个节点Mongo DB副本集的示例，只要5个步骤即可~废话不说了，直接来战~~~
第一步 - 准备环境
准备三个虚拟机，其中一个用作Primary，另外两个用作Secondary。如上图展示的那样~
虚拟机信息如下：
Primary -172.xx.xx.107
Secondary -172.xx.xx.105和172.xx.xx.106
本文的虚拟机装的是CentOS 6.7 ~
第二步 - yum安装Mongo
本文使用yum install mongodb-org命令来安装。
如果遇到No package mongodb-org available.的问题，如：
Loaded plugins: fastestmirror Setting up Install Process Loading mirror speeds from cached hostfile No package mongodb-org available. Error: Nothing to do
在/etc/yum.repos.d/目录下，创建一个mongodb.repo文件，指定MongoDB资源库即可。
使用vim /etc/yum.repos.d/mongodb.repo命令，创建并打开文件mongodb.repo，
[mongodb-org-3.4] name=MongoDB Repository baseurl=https://repo.mongodb.org/yum/redhat/$releasever/mongodb-org/3.4/x86_64/ gpgcheck=1 enabled=1 gpgkey=https://www.mongodb.org/static/pgp/server-3.4.asc
然后，重新使用yum install mongodb-org命令安装即可。
第三步 - 配置副本集
使用vim /etc/mongod.conf配置，每一台虚拟机上的Mongod配置文件。
在replication选项中添加oplogSizeMB 和 replSetName两个属性~
replication: oplogSizeMB: 1024 replSetName: wang
配置文件mongod.conf如下所示：
# mongod.conf
# for documentation of all options,see:
# http://docs.mongodb.org/manual/reference/configuration-options/
# where to write logging data.
systemLog:
destination: file
logAppend: true
path: /var/log/mongodb/mongod.log
# Where and how to store data.
storage:
dbPath: /var/lib/mongo
journal:
enabled: true
# engine:
# mmapv1:
# wiredTiger:
# how the process runs
processManagement:
fork: true # fork and run in background
pidFilePath: /var/run/mongodb/mongod.pid # location of pidfile
# network interfaces
net:
port: 27017
bindIp: 0.0.0.0 # Listen to local interface only,comment to listen on all interfaces.
#security:
#operationProfiling:
replication:
oplogSizeMB: 1024
replSetName: wang
#sharding:
## Enterprise-Only Options
#auditLog:
#snmp:
注意：
3台虚拟机，MongoDB配置文件mongod.conf中的replSetName名字要保持一致，
在本例中，replSetName的名字为wang，这个名字可以随便取~~
第四步 - 启动
配置好副本集之后，通过mongod --config /etc/mongod.conf命令启动三个虚拟机中的Mongo服务~，如：
[root@dev04 mongodb]# mongod --config /etc/mongod.conf about to fork child process,waiting until server is ready for connections. forked process: 30799 child process started successfully,parent exiting
因为107端口的虚拟机安装的MongoDB要用作Primary节点，所以，我们可以使用mongo命令来连接~
[root@dev04 mongodb]# mongo MongoDB shell version v3.4.2 connecting to: mongodb://127.0.0.1:27017 MongoDB server version: 3.4.2 Server has startup warnings: 2017-02-17T09:19:20.240+0800 I STORAGE [initandlisten] 2017-02-17T09:19:20.240+0800 I STORAGE [initandlisten] ** WARNING: Using the XFS filesystem is strongly recommended with the WiredTiger storage engine 2017-02-17T09:19:20.240+0800 I STORAGE [initandlisten] ** See http://dochub.mongodb.org/core/prodnotes-filesystem 2017-02-17T09:19:20.964+0800 I CONTROL [initandlisten] 2017-02-17T09:19:20.964+0800 I CONTROL [initandlisten] ** WARNING: Access control is not enabled for the database. 2017-02-17T09:19:20.964+0800 I CONTROL [initandlisten] ** Read and write access to data and configuration is unrestricted. 2017-02-17T09:19:20.964+0800 I CONTROL [initandlisten] ** WARNING: You are running this process as the root user,which is not recommended. 2017-02-17T09:19:20.965+0800 I CONTROL [initandlisten] 2017-02-17T09:19:20.965+0800 I CONTROL [initandlisten] 2017-02-17T09:19:20.965+0800 I CONTROL [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/enabled is 'always'. 2017-02-17T09:19:20.965+0800 I CONTROL [initandlisten] ** We suggest setting it to 'never' 2017-02-17T09:19:20.965+0800 I CONTROL [initandlisten] 2017-02-17T09:19:20.965+0800 I CONTROL [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/defrag is 'always'. 2017-02-17T09:19:20.965+0800 I CONTROL [initandlisten] ** We suggest setting it to 'never' 2017-02-17T09:19:20.965+0800 I CONTROL [initandlisten]
使用use admin,切换到时admin数据库，
> use admin switched to db admin
然后通过config配置设置副本集节点成员~~
config={_id:"wang",members:[{_id:0,host:"172.xxx.xxx.107:27017"},{_id:1,host:"172.xxx.xxx.106:27017"},{_id:2,host:"172.xxx.xxx.105:27017"}]}
注：
_id:"wang",wang是副本集中取得名字。
members中添加每个副本集Mongod的_id和host信息
执行完上述信息，会出现如下信息：
> config={_id:"wang",host:"172.xxx.xxx.105:27017"}]}
{
"_id" : "wang","members" : [
{
"_id" : 0,"host" : "172.xxx.xxx.107:27017"
},{
"_id" : 1,"host" : "172.xxx.xxx.106:27017"
},{
"_id" : 2,"host" : "172.xxx.xxx.105:27017"
}
]
}
>
然后，执行配置初始化，看到{ "ok" : 1 }，则表明初始化成功~
> rs.initiate(config)
{ "ok" : 1 }
使用rs.status()查看副本节点状态~~
wang:PRIMARY> rs.status()
{
"set" : "wang","date" : ISODate("2017-02-17T01:30:53.128Z"),"myState" : 1,"term" : NumberLong(1),"heartbeatIntervalMillis" : NumberLong(2000),"optimes" : {
"lastCommittedOpTime" : {
"ts" : Timestamp(1487295047,1),"t" : NumberLong(1)
},"appliedOpTime" : {
"ts" : Timestamp(1487295047,"durableOpTime" : {
"ts" : Timestamp(1487295047,"t" : NumberLong(1)
}
},"name" : "172.xxx.xxx.107:27017","health" : 1,"state" : 1,"stateStr" : "PRIMARY","uptime" : 693,"optime" : {
"ts" : Timestamp(1487295047,"t" : NumberLong(1)
},"optimeDate" : ISODate("2017-02-17T01:30:47Z"),"infoMessage" : "could not find member to sync from","electionTime" : Timestamp(1487294966,"electionDate" : ISODate("2017-02-17T01:29:26Z"),"configVersion" : 1,"self" : true
},"name" : "172.xxx.xxx.106:27017","state" : 2,"stateStr" : "SECONDARY","uptime" : 96,"optimeDurable" : {
"ts" : Timestamp(1487295047,"optimeDurableDate" : ISODate("2017-02-17T01:30:47Z"),"lastHeartbeat" : ISODate("2017-02-17T01:30:52.708Z"),"lastHeartbeatRecv" : ISODate("2017-02-17T01:30:51.674Z"),"pingMs" : NumberLong(0),"syncingTo" : "172.xxx.xxx.107:27017","configVersion" : 1
},"name" : "172.xxx.xxx.105:27017","lastHeartbeatRecv" : ISODate("2017-02-17T01:30:51.745Z"),"syncingTo" : "172.xxx.xxx.106:27017","configVersion" : 1
}
],"ok" : 1
}
wang:PRIMARY>
从上图圈出来的信息可以看出，一个Primary 和两个Secondary的副本集已经完成~~~
第五步 - 验证
最后一步就是用来验证了,看看数据能否同步过来~~~
写的操作是在Primary节点上操作的。
在107节点上，创建一个messages的数据库，然后在message Collection中插入两条message。
wang:PRIMARY> show dbs
admin 0.000GB
local 0.000GB
wang:PRIMARY> use messages
switched to db messages
wang:PRIMARY> db.message.insert({"name":"This is a test message"})
WriteResult({ "nInserted" : 1 })
wang:PRIMARY> show dbs
admin 0.000GB
local 0.000GB
messages 0.000GB
wang:PRIMARY> db.message.insert({"name":"This is a test message111"})
WriteResult({ "nInserted" : 1 })
wang:PRIMARY>
通过可视化工具查看，Secondary节点105和106上是否可以同步Primary节点107上messages数据库的信息~~
详细信息如下：
从可视化工具的截图可以看出，两个Secondary节点105和106，与Primary节点107，拥有同样的数据集~~ 至此，Mongo DB副本集的环境搭建完成~~~
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