Mongodb Replica Set集群简介

Mongodb ReplicaSet 集群由Primary,Secondary,Arbiter这3个角色组成，如下图所示：

• Primary:主节点，可读可写，负责数据的写入，并将数据同步复制到Secondary节点上
• Secondary：从节点，只能提供数据的读取操作，当主节点异常时可以迅速切换为主节点。
• Arbiter：观察者节点，负责投票选举出主节点。
  这3类节点之间通过互相发送心跳包保持连接记录相互之间的状态。当主节点崩溃时，观察者节点负责投票选举出合适的从节点为主节点，保证整个集群的可用性。

Mongodb集群搭建

环境准备

假设有3台机器，如下所示

安装Mongodb

从Mongodb的官方网站上下载Mongodb，在192.168.0.109服务器上执行如下操作

[root@localhost software]# wget https://fastdl.mongodb.org/linux/mongodb-linux-x86_64-rhel70-4.4.6.tgz
[root@localhost software]# tar -xvf mongodb-linux-x86_64-rhel70-4.4.6.tgz 
mongodb-linux-x86_64-rhel70-4.4.6/LICENSE-Community.txt
mongodb-linux-x86_64-rhel70-4.4.6/MPL-2
mongodb-linux-x86_64-rhel70-4.4.6/README
mongodb-linux-x86_64-rhel70-4.4.6/THIRD-PARTY-NOTICES
mongodb-linux-x86_64-rhel70-4.4.6/bin/install_compass
mongodb-linux-x86_64-rhel70-4.4.6/bin/mongo
mongodb-linux-x86_64-rhel70-4.4.6/bin/mongod
mongodb-linux-x86_64-rhel70-4.4.6/bin/mongos
[root@localhost software]# ls
mongodb-linux-x86_64-rhel70-4.4.6  mongodb-linux-x86_64-rhel70-4.4.6.tgz
[root@localhost software]# mv mongodb-linux-x86_64-rhel70-4.4.6 mongodb-4.4.6
[root@localhost software]# mv mongodb-4.4.6/ /home/
[root@localhost software]# cd /home/mongodb-4.4.6/
[root@localhost mongodb-4.4.6]# ls
bin  LICENSE-Community.txt  MPL-2  README  THIRD-PARTY-NOTICES
[root@localhost mongodb-4.4.6]# mkdir conf 
[root@localhost mongodb-4.4.6]# mkdir data
[root@localhost mongodb-4.4.6]# mkdir log
[root@localhost mongodb-4.4.6]# cd conf 
[root@localhost conf]# touch mongodb.conf
#编辑配置文件
[root@localhost conf]# vi mongodb.conf

mongodb.conf配置文件

配置文件内容如下：

dbpath=/home/mongodb/data
logpath=/home/mongodb/log/mongodb.log
directoryperdb=true
logappend=true
replSet=Zealink   
bind_ip=0.0.0.0
port=27017
oplogSize=10000
fork=true

说明：

• replSet 为集群的名称
• dbpath 为数据文件存放的目录
• logpath 为日志文件存放的位置，此处是一个完整的文件的地址，不是目录
• bind_ip 服务绑定的ip地址
• port mongdb监听的端口号，默认是27017
• fork=true 以守护进程的方式运行

启动mongdb服务器

[root@localhost bin]# /home/mongodb-4.4.6/bin/mongod -f /home/mongodb-4.4.6/conf/mongodb.conf 

如此，mongodb服务安装完毕，在其他两台服务器上执行上述操作。

集群初始化

在3台服务器上随便选择一台，使用mongo客户端连接到mongodb服务器

[root@localhost bin]#/home/mongodb-4.4.6/bin/mongo -port 28010
MongoDB shell version:1.8.1
connecting to:127.0.0.1:28010/test
>config_rs1={_id:'Zealink',members:[
...{_id:0,host:'192.168.0.109:27017',priority:2},
...{_id:1,host:'192.168.0.109:27017',priority:1},
...{_id:2,host:'192.168.0.109:27017',arbiterOnly:true}]
...
}
>rs.initiate(config_rs1);
{
"info":"Config now saved locally.Should come online in about a minute.",
"ok":1
}
>rs.status()
{
	"set" : "Zealink",
	"date" : ISODate("2021-08-26T16:49:53.176Z"),
	"myState" : 1,
	"term" : NumberLong(5),
	"syncSourceHost" : "",
	"syncSourceId" : -1,
	"heartbeatIntervalMillis" : NumberLong(2000),
	"majorityVoteCount" : 2,
	"writeMajorityCount" : 2,
	"votingMembersCount" : 3,
	"writableVotingMembersCount" : 2,
	"optimes" : {
		"lastCommittedOpTime" : {
			"ts" : Timestamp(1629996585, 1),
			"t" : NumberLong(5)
		},
		"lastCommittedWallTime" : ISODate("2021-08-26T16:49:45.722Z"),
		"readConcernMajorityOpTime" : {
			"ts" : Timestamp(1629996585, 1),
			"t" : NumberLong(5)
		},
		"readConcernMajorityWallTime" : ISODate("2021-08-26T16:49:45.722Z"),
		"appliedOpTime" : {
			"ts" : Timestamp(1629996585, 1),
			"t" : NumberLong(5)
		},
		"durableOpTime" : {
			"ts" : Timestamp(1629996585, 1),
			"t" : NumberLong(5)
		},
		"lastAppliedWallTime" : ISODate("2021-08-26T16:49:45.722Z"),
		"lastDurableWallTime" : ISODate("2021-08-26T16:49:45.722Z")
	},
	"lastStableRecoveryTimestamp" : Timestamp(1629996532, 1),
	"electionCandidateMetrics" : {
		"lastElectionReason" : "priorityTakeover",
		"lastElectionDate" : ISODate("2021-08-09T01:40:40.529Z"),
		"electionTerm" : NumberLong(5),
		"lastCommittedOpTimeAtElection" : {
			"ts" : Timestamp(1628473230, 1),
			"t" : NumberLong(4)
		},
		"lastSeenOpTimeAtElection" : {
			"ts" : Timestamp(1628473230, 1),
			"t" : NumberLong(4)
		},
		"numVotesNeeded" : 2,
		"priorityAtElection" : 3,
		"electionTimeoutMillis" : NumberLong(10000),
		"priorPrimaryMemberId" : 1,
		"targetCatchupOpTime" : {
			"ts" : Timestamp(1628473240, 1),
			"t" : NumberLong(4)
		},
		"numCatchUpOps" : NumberLong(1),
		"newTermStartDate" : ISODate("2021-08-09T01:40:41.343Z"),
		"wMajorityWriteAvailabilityDate" : ISODate("2021-08-09T01:40:41.689Z")
	},
	"members" : [
		{
			"_id" : 0,
			"name" : "192.168.0.109:27017",
			"health" : 1,
			"state" : 1,
			"stateStr" : "PRIMARY",
			"uptime" : 1523462,
			"optime" : {
				"ts" : Timestamp(1629996585, 1),
				"t" : NumberLong(5)
			},
			"optimeDate" : ISODate("2021-08-26T16:49:45Z"),
			"syncSourceHost" : "",
			"syncSourceId" : -1,
			"infoMessage" : "",
			"electionTime" : Timestamp(1628473240, 1),
			"electionDate" : ISODate("2021-08-09T01:40:40Z"),
			"configVersion" : 1,
			"configTerm" : 5,
			"self" : true,
			"lastHeartbeatMessage" : ""
		},
		{
			"_id" : 1,
			"name" : "192.168.0.110:27017",
			"health" : 1,
			"state" : 2,
			"stateStr" : "SECONDARY",
			"uptime" : 1519722,
			"optime" : {
				"ts" : Timestamp(1629996585, 1),
				"t" : NumberLong(5)
			},
			"optimeDurable" : {
				"ts" : Timestamp(1629996585, 1),
				"t" : NumberLong(5)
			},
			"optimeDate" : ISODate("2021-08-26T16:49:45Z"),
			"optimeDurableDate" : ISODate("2021-08-26T16:49:45Z"),
			"lastHeartbeat" : ISODate("2021-08-26T16:49:52.993Z"),
			"lastHeartbeatRecv" : ISODate("2021-08-26T16:49:52.998Z"),
			"pingMs" : NumberLong(0),
			"lastHeartbeatMessage" : "",
			"syncSourceHost" : "192.168.0.110:27017",
			"syncSourceId" : 0,
			"infoMessage" : "",
			"configVersion" : 1,
			"configTerm" : 5
		},
		{
			"_id" : 3,
			"name" : "192.168.0.111:27017",
			"health" : 1,
			"state" : 7,
			"stateStr" : "ARBITER",
			"uptime" : 1523459,
			"lastHeartbeat" : ISODate("2021-08-26T16:49:51.559Z"),
			"lastHeartbeatRecv" : ISODate("2021-08-26T16:49:52.451Z"),
			"pingMs" : NumberLong(0),
			"lastHeartbeatMessage" : "",
			"syncSourceHost" : "",
			"syncSourceId" : -1,
			"infoMessage" : "",
			"configVersion" : 1,
			"configTerm" : 5
		}
	],
	"ok" : 1,
	"$clusterTime" : {
		"clusterTime" : Timestamp(1629996585, 1),
		"signature" : {
			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
			"keyId" : NumberLong(0)
		}
	},
	"operationTime" : Timestamp(1629996585, 1)
}

• rs.status()通过这个命令可以查看集群的状态，各个成员节点的状态是否正常。

• rs.stepDown()这个命令可以强制primary和standard节点角色互换，从而验证是否能够实现failover功能。或者primary上执行 use admin;db.shutdownServer();断掉primary看效果。

• rs.isMaster()显示当前哪个节点是primary节点

MongoDB replica sets中通过设置priority的值来决定优先权的大小,这个值的范围是0–100,值越大,优先权越高。

设置开机自启动服务

默认情况下mongdb是以普通程序运行的，如果服务器异常重启，需要手工去启动程序，给运维造成了极大的不便，所以我们需要将其配置为服务运行的方式，并设置成为开机自启动。

• 在/etc/init.d/目录下创建mongodb 文件，文件的内容如下所示:

#!/bin/sh
#
#mongod - Startup script for mongod
#
# chkconfig: - 85 15
# description: Mongodb database.
# processname: mongod
# Source function library
 
. /etc/rc.d/init.d/functions
# things from mongod.conf get there by mongod reading it
# OPTIONS
OPTIONS=" --config /home/mongodb-4.4.6/conf/mongodb.conf  &"
#mongod
mongod="/home/mongodb-4.4.6/bin/mongo"
lockfile=/var/lock/subsys/mongod
start()
{
  echo -n $"Starting mongod-arbiter: "
  daemon $mongod $OPTIONS
  RETVAL=$?
  echo
  [ $RETVAL -eq 0 ] && touch $lockfile
}
 
stop()
{
  echo -n $"Stopping mongod-arbiter: "
  killproc $mongod -QUIT
  RETVAL=$?
  echo
  [ $RETVAL -eq 0 ] && rm -f $lockfile
}
 
restart () {
        stop
        start
}
ulimit -n 12000
RETVAL=0
 
case "$1" in
  start)
    start
    ;;
  stop)
    stop
    ;;
  restart|reload|force-reload)
    restart
    ;;
  condrestart)
    [ -f $lockfile ] && restart || :
    ;;
  status)
    status $mongod
    RETVAL=$?
    ;;
  *)
    echo "Usage: $0 {start|stop|status|restart|reload|force-reload|condrestart}"
    RETVAL=1
esac
exit $RETVAL

• 添加可执行权限 chmod +x mongodb
• 设置开机自启动 systemctl enable mongodb
• systemctl start mongodb 开启Mongodb服务
• systemctl stop mongodb 关闭Mongodb服务