MongoDB复制集（即主从复制）

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。

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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

for i in 1 2 3 4
do
        mongod -f /data/conf/mongodb$i.conf
done

检查mongod的进程信息

[root@localhost 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：如以上可知道主节点在192.168.100.100:27017节点上

注意：严禁在从库做任何修改操作

7. 添加节点

test-rc:PRIMARY>  rs.add("192.168.100.100:27020")

查看复制集的状态信息

test-rc:PRIMARY>  rs.status()

8. 删除节点

test-rc:PRIMARY>  rs.remove("192.168.100.100:27018")

查看复制集的状态信息

test-rc:PRIMARY>  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

test-rc:PRIMARY>  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'  :
DB.prototype.runCommand@src/mongo/shell/db.js:168:1
DB.prototype.adminCommand@src/mongo/shell/db.js:186:16
rs.stepDown@src/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