MongoDB复制集 （主从复制）

Posted 2020-12-04

MongoDB 复制集

MongoDB复制是将数据同步到多个服务器的过程；
复制集提供了数据的冗余备份并提高了数据的可用性，通常可以保证数据的安全性；
复制集还允许您从硬件故障和服务中断中恢复数据。

什么是复制集?

• 保障数据的安全性
• 数据高可用性 (24*7)
• 灾难恢复
• 无需停机维护（如备份，重建索引，压缩）
• 分布式读取数据
• 副本集对应用层是透明的

MongoDB复制集的工作原理

1. mongodb的复制集至少需要两个节点。其中一个是主节点，负责处理客户端请求，其余的都是从节点，负责复制主节点上的数据。
2. mongodb各个节点常见的搭配方式为：一主一从、一主多从。
3. 主节点记录在其上的所有操作oplog，从节点定期轮询主节点获取这些操作，然后对自己的数据副本执行这些操作，从而保证从节点的数据与主节点一致。

MongoDB复制结构图如下所示：

（以上图片引用网址：http://www.runoob.com/mongodb/mongodb-replication.html ）

以上结构图中，客户端从主节点读取数据，在客户端写入数据到主节点时，主节点与从节点进行数据交互保障数据的一致性。

复制集的特点：

• N 个节点的集群
• 任何节点可作为主节点
• 所有写入操作都在主节点上
• 自动故障转移
• 自动恢复

如何部署MongoDB复制集？

在同一台服务器上创建MongoDB的多实例（4个实例）来做MongoDB主从的实验。

至于如何安装MongoDB？请参考之前博文 Linux 平台安装MongoDB 4.0（最新版）

开始部署

1.创建4个MongoDB的实例

#创建各实例的数据目录
mkdir -p /data/mongodb/mongodb{1,2,3,4}

#创建实例配置目录
mkdir -p /data/conf/

#创建实例的日志目录
mkdir -p /data/logs/

#创建各实例的日志文件
touch  /data/logs/mongodb{1,2,3,4}.log

#赋予日志文件权限777
chmod 777 /data/logs/*.log

2.编辑mongodb1.conf配置文件，开启复制集功能并配置replSetName参数

vim /data/mongodb/mongodb1.conf

#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: /data/logs/mongodb1.log //mongodb1的日志文件路径
#Where and how to store data.
storage:
dbPath: /data/mongodb/mongodb1/ //mongodb1的数据文件路径
journal:
enabled: true
#engine:
#mmapv1:
#wiredTiger:
#how the process runs
processManagement:
fork: true # fork and run in background
pidFilePath: /data/mongodb/mongodb1/mongod.pid # location of pidfile
timeZoneInfo: /usr/share/zoneinfo
#network interfaces
net:
port: 27017 //mongodb1的进程号
bindIp: 0.0.0.0 # Listen to local interface only, comment to listen on all interfaces.
#security:
#operationProfiling:
replication: //删除“#”，开启复制集功能
replSetName: test-rc //名称为test-rc
#sharding:
##Enterprise-Only Options
#auditLog:
#snmp:

3.复制默认mongodb1.conf配置文件，生成另外三份实例的配置文件

#复制默认实例的配置文件

cp -p /data/mongodb/mongodb1.conf /data/conf/mongodb2.conf
cp -p /data/mongodb/mongodb1.conf /data/conf/mongodb3.conf
cp -p /data/mongodb/mongodb1.conf /data/conf/mongodb4.conf

4.分别修改mongodb2.conf、mongodb3.conf、mongodb4.conf配置文件，如下

MongoDB2配置文件

cat /data/conf/mongodb2.conf

#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: /data/logs/mongodb2.log //mongodb2的日志文件路径
#Where and how to store data.
storage:
dbPath: /data/mongodb/mongodb2/ //mongodb2的数据文件路径
journal:
enabled: true
#engine:
#mmapv1:
#wiredTiger:
#how the process runs
processManagement:
fork: true # fork and run in background
pidFilePath: /data/mongodb/mongodb1/mongod.pid # location of pidfile
timeZoneInfo: /usr/share/zoneinfo
#network interfaces
net:
port: 27018 //mongodb2的进程号
bindIp: 0.0.0.0 # Listen to local interface only, comment to listen on all interfaces.
#security:
#operationProfiling:
replication: //删除“#”，开启复制集功能
replSetName: test-rc #名称为test-rc
#sharding:
##Enterprise-Only Options
#auditLog:
#snmp:

MongoDB3配置文件

cat /data/conf/mongodb3.conf

#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: /data/logs/mongodb3.log //mongodb3的日志文件路径
#Where and how to store data.
storage:
dbPath: /data/mongodb/mongodb3/ //mongodb3的数据文件路径
journal:
enabled: true
#engine:
#mmapv1:
#wiredTiger:
#how the process runs
processManagement:
fork: true # fork and run in background
pidFilePath: /data/mongodb/mongodb1/mongod.pid # location of pidfile
timeZoneInfo: /usr/share/zoneinfo
#network interfaces
net:
port: 27019 //mongodb3的进程号
bindIp: 0.0.0.0 # Listen to local interface only, comment to listen on all interfaces.
#security:
#operationProfiling:
replication: //删除“#”，开启复制集功能
replSetName: test-rc #名称为test-rc
#sharding:
##Enterprise-Only Options
#auditLog:
#snmp:

MongoDB4配置文件

cat /data/conf/mongodb4.conf

#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: /data/logs/mongodb4.log //mongodb4的日志文件路径
#Where and how to store data.
storage:
dbPath: /data/mongodb/mongodb4/ //mongodb4的数据文件路径
journal:
enabled: true
#engine:
#mmapv1:
#wiredTiger:
#how the process runs
processManagement:
fork: true # fork and run in background
pidFilePath: /data/mongodb/mongodb1/mongod.pid # location of pidfile
timeZoneInfo: /usr/share/zoneinfo
#network interfaces
net:
port: 27020 //mongodb4的进程号
bindIp: 0.0.0.0 # Listen to local interface only, comment to listen on all interfaces.
#security:
#operationProfiling:
replication: //删除“#”，开启复制集功能
replSetName: test-rc //名称为test-rc
#sharding:
##Enterprise-Only Options
#auditLog:
#snmp:

5. 启动mongodb多实例

mongod -f /data/conf/mongodb1.conf
mongod -f /data/conf/mongodb2.conf
mongod -f /data/conf/mongodb3.conf
mongod -f /data/conf/mongodb4.conf

检查mongod的进程信息

[[email protected] conf]# netstat -tunlp | grep mongod

6.开始配置三个节点的复制集

6.1 登录默认MongoDB（默认端口号为：27017）

mongo

6.2 查看复制集的状态信息

> rs.status()

6.3 定义cfg初始化参数(这里先加入三台，另一台后面实现添加节点功能)

> cfg={"_id":"test-rc","members":[{"_id":0,"host":"192.168.100.100:27017"},{"_id":1,"host":"192.168.100.100:27018"},{"_id":2,"host":"192.168.100.100:27019"}]}

6.4 启动复制集功能（初始化配置时保证从节点没有数据）

> rs.initiate(cfg)

6.5 查看复制集的状态信息

test-rc:PRIMARY> rs.status()

{
"set" : "test-rc",
"date" : ISODate("2018-07-14T04:46:58.710Z"),
"myState" : 1,
"term" : NumberLong(1),
"syncingTo" : "",
"syncSourceHost" : "",
"syncSourceId" : -1,
"heartbeatIntervalMillis" : NumberLong(2000),
"optimes" : {
"lastCommittedOpTime" : {
"ts" : Timestamp(1531543618, 1),
"t" : NumberLong(1)
},
"readConcernMajorityOpTime" : {
"ts" : Timestamp(1531543618, 1),
"t" : NumberLong(1)
},
"appliedOpTime" : {
"ts" : Timestamp(1531543618, 1),
"t" : NumberLong(1)
},
"durableOpTime" : {
"ts" : Timestamp(1531543618, 1),
"t" : NumberLong(1)
}
},
"lastStableCheckpointTimestamp" : Timestamp(1531543608, 1),
"members" : [
{
"_id" : 0,
"name" : "192.168.100.100:27017",
"health" : 1, //健康状态
"state" : 1, //1：为主节点 ； 2：为从节点
"stateStr" : "PRIMARY", //主节点
"uptime" : 2886,
"optime" : {
"ts" : Timestamp(1531543618, 1),
"t" : NumberLong(1)
},
"optimeDate" : ISODate("2018-07-14T04:46:58Z"),
"syncingTo" : "",
"syncSourceHost" : "",
"syncSourceId" : -1,
"infoMessage" : "",
"electionTime" : Timestamp(1531543426, 1),
"electionDate" : ISODate("2018-07-14T04:43:46Z"),
"configVersion" : 1,
"self" : true,
"lastHeartbeatMessage" : ""
},
{
"_id" : 1,
"name" : "192.168.100.100:27018",
"health" : 1, //健康状态
"state" : 2, //1：为主节点 ； 2：为从节点
"stateStr" : "SECONDARY", //从节点
"uptime" : 202,
"optime" : {
"ts" : Timestamp(1531543608, 1),
"t" : NumberLong(1)
},
"optimeDurable" : {
"ts" : Timestamp(1531543608, 1),
"t" : NumberLong(1)
},
"optimeDate" : ISODate("2018-07-14T04:46:48Z"),
"optimeDurableDate" : ISODate("2018-07-14T04:46:48Z"),
"lastHeartbeat" : ISODate("2018-07-14T04:46:56.765Z"),
"lastHeartbeatRecv" : ISODate("2018-07-14T04:46:57.395Z"),
"pingMs" : NumberLong(0),
"lastHeartbeatMessage" : "",
"syncingTo" : "192.168.100.100:27017",
"syncSourceHost" : "192.168.100.100:27017",
"syncSourceId" : 0,
"infoMessage" : "",
"configVersion" : 1
},
{
"_id" : 2,
"name" : "192.168.100.100:27019",
"health" : 1, //健康状态
"state" : 2, //1：为主节点 ； 2：为从节点
"stateStr" : "SECONDARY", //从节点
"uptime" : 202,
"optime" : {
"ts" : Timestamp(1531543608, 1),
"t" : NumberLong(1)
},
"optimeDurable" : {
"ts" : Timestamp(1531543608, 1),
"t" : NumberLong(1)
},
"optimeDate" : ISODate("2018-07-14T04:46:48Z"),
"optimeDurableDate" : ISODate("2018-07-14T04:46:48Z"),
"lastHeartbeat" : ISODate("2018-07-14T04:46:56.769Z"),
"lastHeartbeatRecv" : ISODate("2018-07-14T04:46:57.441Z"),
"pingMs" : NumberLong(0),
"lastHeartbeatMessage" : "",
"syncingTo" : "192.168.100.100:27017",
"syncSourceHost" : "192.168.100.100:27017",
"syncSourceId" : 0,
"infoMessage" : "",
"configVersion" : 1
}
],
"ok" : 1,
"operationTime" : Timestamp(1531543618, 1),
"$clusterTime" : {
"clusterTime" : Timestamp(1531543618, 1),
"signature" : {
"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
"keyId" : NumberLong(0)
}
}
}

特别提醒：主节点在192.168.100.100:27017节点上

7. 添加节点

> rs.add("192.168.100.100:27020")

查看复制集的状态信息

> rs.status()

8. 删除节点

> rs.remove("192.168.100.100:27018")

查看复制集的状态信息

> rs.status()

发现192.168.100.100:27018节点已经没有相关信息了

9. 故障转移切换

9.1 退出MongoDB

test-rc:PRIMARY> exit

9.2 查看mongod进程信息

netstat -tunlp | grep mongod

可以查看到共有4个实例的进程信息

9.3 结束主节点：端口号为27017的进程，检查是否能够自动切换

kill -9 48211        

9.4 登录MongoDB端口号为27019的实例

mongo --port 27019

9.5 查看各节点状态信息

> rs.status()

{
"_id" : 2,
"name" : "192.168.100.100:27019",
"health" : 1,
"state" : 1,
"stateStr" : "PRIMARY",
"uptime" : 1547,
"optime" : {
"ts" : Timestamp(1531544567, 1),
"t" : NumberLong(2)
},
"optimeDate" : ISODate("2018-07-14T05:02:47Z"),
"syncingTo" : "",
"syncSourceHost" : "",
"syncSourceId" : -1,
"infoMessage" : "",
"electionTime" : Timestamp(1531544345, 1),
"electionDate" : ISODate("2018-07-14T04:59:05Z"),
"configVersion" : 3,
"self" : true,
"lastHeartbeatMessage" : ""
},
{
"_id" : 3,
"name" : "192.168.100.100:27020",
"health" : 1,
"state" : 2,
"stateStr" : "SECONDARY",
"uptime" : 700,
"optime" : {
"ts" : Timestamp(1531544567, 1),
"t" : NumberLong(2)
},
"optimeDurable" : {
"ts" : Timestamp(1531544567, 1),
"t" : NumberLong(2)
},
"optimeDate" : ISODate("2018-07-14T05:02:47Z"),
"optimeDurableDate" : ISODate("2018-07-14T05:02:47Z"),
"lastHeartbeat" : ISODate("2018-07-14T05:02:56.150Z"),
"lastHeartbeatRecv" : ISODate("2018-07-14T05:02:56.289Z"),
"pingMs" : NumberLong(0),
"lastHeartbeatMessage" : "",
"syncingTo" : "192.168.100.100:27019",
"syncSourceHost" : "192.168.100.100:27019",
"syncSourceId" : 2,
"infoMessage" : "",
"configVersion" : 3
}

特别提醒：主节点已经到192.168.100.100:27019节点上，说明主节点已经自动切换了

10. 手动切换主节点

10.1 暂停30s不参与选举

test-rc:PRIMARY> rs.freeze(30)

{
"operationTime" : Timestamp(1531544867, 1),
"ok" : 0,
"errmsg" : "cannot freeze node when primary or running for election. state: Primary",
"code" : 95,
"codeName" : "NotSecondary",
"$clusterTime" : {
"clusterTime" : Timestamp(1531544867, 1),
"signature" : {
"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
"keyId" : NumberLong(0)
}
}
}

10.2 交出主节点位置，维持从节点状态不少于60秒，等待30秒使主节点和从节点日志同步

test-rc:PRIMARY> rs.stepDown(60,30)

> test-rc:PRIMARY> rs.stepDown(60,30)

2018-07-14T01:08:07.326-0400 E QUERY [js] Error: error doing query: failed: network error while attempting to run command ‘replSetStepDown‘ on host ‘127.0.0.1:27019‘ :br/>[email protected]/mongo/shell/db.js:168:1
[email protected]/mongo/shell/db.js:186:16br/>[email protected]/mongo/shell/utils.js:1398:12
@(shell):1:1
2018-07-14T01:08:07.328-0400 I NETWORK [js] trying reconnect to 127.0.0.1:27019 failed
2018-07-14T01:08:07.329-0400 I NETWORK [js] reconnect 127.0.0.1:27019 ok

10.3 查看复制集的状态信息

> test-rc:PRIMARY> rs.status()

{
"set" : "test-rc",
"date" : ISODate("2018-07-14T05:10:31.161Z"),
"myState" : 2,
"term" : NumberLong(3),
"syncingTo" : "192.168.100.100:27020",
"syncSourceHost" : "192.168.100.100:27020",
"syncSourceId" : 3,
"heartbeatIntervalMillis" : NumberLong(2000),
"optimes" : {
"lastCommittedOpTime" : {
"ts" : Timestamp(1531545028, 1),
"t" : NumberLong(3)
},
"readConcernMajorityOpTime" : {
"ts" : Timestamp(1531545028, 1),
"t" : NumberLong(3)
},
"appliedOpTime" : {
"ts" : Timestamp(1531545028, 1),
"t" : NumberLong(3)
},
"durableOpTime" : {
"ts" : Timestamp(1531545028, 1),
"t" : NumberLong(3)
}
},
"lastStableCheckpointTimestamp" : Timestamp(1531545018, 1),
"members" : [
{
"_id" : 0,
"name" : "192.168.100.100:27017",
"health" : 1,
"state" : 2,
"stateStr" : "SECONDARY",
"uptime" : 70,
"optime" : {
"ts" : Timestamp(1531545028, 1),
"t" : NumberLong(3)
},
"optimeDate" : ISODate("2018-07-14T05:10:28Z"),
"syncingTo" : "192.168.100.100:27020",
"syncSourceHost" : "192.168.100.100:27020",
"syncSourceId" : 3,
"infoMessage" : "",
"configVersion" : 3,
"self" : true,
"lastHeartbeatMessage" : ""
},
{
"_id" : 2,
"name" : "192.168.100.100:27019",
"health" : 1,
"state" : 2,
"stateStr" : "SECONDARY",
"uptime" : 68,
"optime" : {
"ts" : Timestamp(1531545028, 1),
"t" : NumberLong(3)
},
"optimeDurable" : {
"ts" : Timestamp(1531545028, 1),
"t" : NumberLong(3)
},
"optimeDate" : ISODate("2018-07-14T05:10:28Z"),
"optimeDurableDate" : ISODate("2018-07-14T05:10:28Z"),
"lastHeartbeat" : ISODate("2018-07-14T05:10:30.079Z"),
"lastHeartbeatRecv" : ISODate("2018-07-14T05:10:31.094Z"),
"pingMs" : NumberLong(0),
"lastHeartbeatMessage" : "",
"syncingTo" : "192.168.100.100:27020",
"syncSourceHost" : "192.168.100.100:27020",
"syncSourceId" : 3,
"infoMessage" : "",
"configVersion" : 3
},
{
"_id" : 3,
"name" : "192.168.100.100:27020",
"health" : 1,
"state" : 1,
"stateStr" : "PRIMARY",
"uptime" : 68,
"optime" : {
"ts" : Timestamp(1531545028, 1),
"t" : NumberLong(3)
},
"optimeDurable" : {
"ts" : Timestamp(1531545028, 1),
"t" : NumberLong(3)
},
"optimeDate" : ISODate("2018-07-14T05:10:28Z"),
"optimeDurableDate" : ISODate("2018-07-14T05:10:28Z"),
"lastHeartbeat" : ISODate("2018-07-14T05:10:30.079Z"),
"lastHeartbeatRecv" : ISODate("2018-07-14T05:10:29.561Z"),
"pingMs" : NumberLong(0),
"lastHeartbeatMessage" : "",
"syncingTo" : "",
"syncSourceHost" : "",
"syncSourceId" : -1,
"infoMessage" : "",
"electionTime" : Timestamp(1531544897, 1),
"electionDate" : ISODate("2018-07-14T05:08:17Z"),
"configVersion" : 3
}
],
"ok" : 1,
"operationTime" : Timestamp(1531545028, 1),
"$clusterTime" : {
"clusterTime" : Timestamp(1531545028, 1),
"signature" : {
"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
"keyId" : NumberLong(0)
}
}
}

特别提醒：此刻主节点已经在192.168.100.100:27020节点上