详解MongoDB复制集

何为复制集？

复制集是额外的数据副本，是跨多个服务器同步数据的过程，复制集提供了冗余并增加了数据可用性，通过复制集可以对硬件故障和中断的服务进行恢复。

复制集主从同步的原理和mysql类似，主节点记录在其上的所有操作到oplog中，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。

复制集的优势如下：

（1）让数据更安全

（2）高数据可用性（24*7）

（3）灾难恢复

（4）无停机维护（如备份、索引重建、故障转移）

（5）读缩放（额外的副本读取）

（6）副本集对应用程序是透明。

MongoDB复制集结构原理图分析

• .mongodb的复制集至少需要两个节点。其中一个是主节点(Primary)，负责处理客户端请求，其余的都是从节点(Secondary)，负责复制主节点上的数据。

• mongodb各个节点常见的搭配方式为：一主一从或一主多从。

• 客户端在主节点写入数据，在从节点读取数据，主节点与从节点进行数据交互，保障数据的一致性。如果其中一个节点出现故障，其他节点马上会将业务接过来而无需停机操作

复制集的特点：

1.N 个节点的集群

2.任何节点可作为主节点

3.所有写入操作都在主节点上

4.自动故障转移

5.自动恢复

MongoDB复制集部署

• 在一台CentOS7主机上使用yum在线安装Mongodb，并创建多实例，进行部署MongoDB复制集

首先配置网络YUM源，baseurl（下载路径）指定为mongodb官网提供的yum仓库

vim /etc/yum.repos.d/mongodb.repo

[mongodb-org]

name=MongoDB Repository

baseurl=https://repo.mongodb.org/yum/redhat/$releasever/mongodb-org/3.6/x86_64/             #指定获得下载的路径

gpgcheck=1                     #表示对从这个源下载的rpm包进行校验

enabled=1                   #表示启用这个源。

gpgkey=https://www.mongodb.org/static/pgp/server-3.6.asc

重新加载yum源，并使用yum命令下载安装mongodb

yum list

yum -y install mongodb-org

准备4个实例，暂时开启3个， 1主2从    再额外添加群集（追加实例）也可以撤销实例

• 创建数据文件和日志文件存储路径，并赋予权限

  
  [root@localhost ~]# mkdir -p /data/mongodb{2,3,4}
  [root@localhost ~]# mkdir /data/logs
  [root@localhost ~]# touch /data/logs/mongodb{2,3,4}.log
  [root@localhost ~]# chmod 777 /data/logs/mongodb*
  [root@localhost ~]# ll /data/logs/
  总用量 0
  -rwxrwxrwx. 1 root root 0 9月  15 22:31 mongodb2.log
  -rwxrwxrwx. 1 root root 0 9月  15 22:31 mongodb3.log
  -rwxrwxrwx. 1 root root 0 9月  15 22:31 mongodb4.log

编辑4个MongoDB实例的配置文件

• 先编辑yum安装的默认实例的配置文件/etc/mongod.conf，指定监听IP，端口默认为27017，开启replication参数配置，replSetName：true（自定义）

[root@localhost ~]# vim /etc/mongod.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: /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
  timeZoneInfo: /usr/share/zoneinfo

# network interfaces
net: 

  port: 27017                    #默认端口         
  bindIp: 0.0.0.0             #监听任意地址

#security:

#operationProfiling:

replication:                   #去掉前面的“#”注释，开启该参数设置
replSetName: true          #设置复制集名称

• 复制配置文件给其他实例，并将mongodb2.conf 中的port参数配置为27018，mongod3.conf中的port参数配置为27019，mongod4.conf中的port参数配置为27020。 同样也将dbpath和logpath参数修改为对应的路径值

cp  /etc/mongod.conf /etc/mongod2.conf

cp /etc/mongod2.conf /etc/mongod3.conf

cp /etc/mongod2.conf /etc/mongod4.conf

• 实例2的配置文件mongodb2.conf 修改

vim /etc/mongod2.conf

systemLog:

  destination: file

  logAppend: true

  path: /data/logs/mongodb2.log    

storage:

  dbPath: /data/mongodb/mongodb2  

  journal:

enabled: true

port: 27018 

bindIp: 0.0.0.0  # Listen to local interface only, comment to listen on all interfaces.

#security:

#operationProfiling:

replication:
replSetName: true

• 实例3的配置文件mongodb3.conf 修改

vim /etc/mongod3.conf

systemLog:

  destination: file

  logAppend: true

  path: /data/logs/mongodb3.log    

storage:

  dbPath: /data/mongodb/mongodb3 

  journal:

enabled: true

port: 27019 

bindIp: 0.0.0.0  # Listen to local interface only, comment to listen on all interfaces.

#security:

#operationProfiling:

replication:
replSetName: true

• 实例4的配置文件mongodb4.conf 修改

vim /etc/mongod4.conf

systemLog:

  destination: file

  logAppend: true

  path: /data/logs/mongodb4.log    

storage:

  dbPath: /data/mongodb/mongodb4  

  journal:

enabled: true

port: 27020 

bindIp: 0.0.0.0  # Listen to local interface only, comment to listen on all interfaces.

#security:

#operationProfiling:

replication:
replSetName: true

启动mongodb各实例

[root@localhost ~]# mongod -f /etc/mongod.conf
about to fork child process, waiting until server is ready for connections.
forked process: 93576
child process started successfully, parent exiting
[root@localhost ~]# mongod -f /etc/mongod2.conf
about to fork child process, waiting until server is ready for connections.
forked process: 93608
child process started successfully, parent exiting
[root@localhost ~]# mongod -f /etc/mongod3.conf
about to fork child process, waiting until server is ready for connections.
forked process: 93636
child process started successfully, parent exiting
[root@localhost ~]# mongod -f /etc/mongod4.conf
about to fork child process, waiting until server is ready for connections.
forked process: 93664
child process started successfully, parent exiting
[root@localhost ~]# netstat -antp | grep mongod                        //查看mongodb进程状态
tcp        0      0 0.0.0.0:27019           0.0.0.0:*               LISTEN      93636/mongod       
tcp        0      0 0.0.0.0:27020           0.0.0.0:*               LISTEN      93664/mongod       
tcp        0      0 0.0.0.0:27017           0.0.0.0:*               LISTEN      93576/mongod       
tcp        0      0 0.0.0.0:27018           0.0.0.0:*               LISTEN      93608/mongod

配置三个节点的复制集

[root@localhost ~]# mongo                     //进入其中一个实例
MongoDB shell version v3.6.7
connecting to: mongodb://127.0.0.1:27017
MongoDB server version: 3.6.7

> rs.status()                               //查看复制集状态，提示复制集还未配置
{
    "info" : "run rs.initiate(...) if not yet done for the set",
    "ok" : 0,
    "errmsg" : "no replset config has been received",
    "code" : 94,
    "codeName" : "NotYetInitialized",
    "operationTime" : Timestamp(0, 0),
    "$clusterTime" : {
        "clusterTime" : Timestamp(0, 0),
        "signature" : {
            "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
            "keyId" : NumberLong(0)
        }
    }

> cfg={"_id":"true","members":[{"_id":0,"host":"192.168.195.137:27017"},{"_id":1,"host":"192.168.195.137:27018"},{"_id":2,"host":"192.168.195.137:27019"}]}                    // 定义cfg初始化参数                    
{
    "_id" : "true",
    "members" : [
        {
            "_id" : 0,
            "host" : "192.168.195.137:27017"
        },
        {
            "_id" : 1,
            "host" : "192.168.195.137:27018"
        },
        {
            "_id" : 2,
            "host" : "192.168.195.137:27019"
        }
    ]
}

> rs.initiate(cfg)                    //初始化并启动复制集

{"ok" : 1}

true:PRIMARY> rs.status()               //再次查看复制集的状态信息
{
    "set" : "true",
    "date" : ISODate("2018-09-15T15:39:48.426Z"),
    "myState" : 1,
    "term" : NumberLong(1),
    "syncingTo" : "",
    "syncSourceHost" : "",
    "syncSourceId" : -1,
    "heartbeatIntervalMillis" : NumberLong(2000),
    "optimes" : {
        "lastCommittedOpTime" : {
            "ts" : Timestamp(1537025984, 1),
            "t" : NumberLong(1)
        },
        "readConcernMajorityOpTime" : {
            "ts" : Timestamp(1537025984, 1),
            "t" : NumberLong(1)
        },
        "appliedOpTime" : {
            "ts" : Timestamp(1537025984, 1),
            "t" : NumberLong(1)
        },
        "durableOpTime" : {
            "ts" : Timestamp(1537025984, 1),
            "t" : NumberLong(1)
        }
    },
    "members" : [
        {
            "_id" : 0,
           "name" : "192.168.195.137:27017",
            "health" : 1,
            "state" : 1,
           "stateStr" : "PRIMARY",              //此节点成为主节点
            "uptime" : 1371,
            "optime" : {
                "ts" : Timestamp(1537025984, 1),
                "t" : NumberLong(1)
            },

....................

                  {
            "_id" : 1,
            "name" : "192.168.195.137:27018",
            "health" : 1,
            "state" : 2,
           "stateStr" : "SECONDARY",                //此节点为从节点
            "uptime" : 18,
            "optime" : {
                "ts" : Timestamp(1537025984, 1),
                "t" : NumberLong(1)
            },
            "optimeDurable" : {
                "ts" : Timestamp(1537025984, 1),
                "t" : NumberLong(1)
            },

...................

                 {
            "_id" : 2,
            "name" : "192.168.195.137:27019",
            "health" : 1,
            "state" : 2,
           "stateStr" : "SECONDARY",                   //此节点为从节点
            "uptime" : 18,
            "optime" : {
                "ts" : Timestamp(1537025984, 1),
                "t" : NumberLong(1)
            },
            "optimeDurable" : {
                "ts" : Timestamp(1537025984, 1),
                "t" : NumberLong(1)
            },
         

• 添加节点

true:PRIMARY> rs.add("192.168.195.137:27020")

true:PRIMARY> rs.status()

..............

{
            "_id" : 3,
            "name" : "192.168.195.137:27020",
            "health" : 1,
            "state" : 2,
            "stateStr" : "SECONDARY",
            "uptime" : 8,
            "optime" : {
                "ts" : Timestamp(1537026818, 1),
                "t" : NumberLong(1)
            },
            "optimeDurable" : {
                "ts" : Timestamp(1537026818, 1),
                "t" : NumberLong(1)
            },

.................

• 删除节点

true:PRIMARY> rs.remove("192.168.195.137:27020")

模拟故障自动转移切换

[root@localhost ~]# mongod -f /etc/mongod.conf --shutdown              //关闭主节点服务
killing process with pid: 93576
[root@localhost ~]# mongo --port 27018                      //进入其中一个从节点
MongoDB shell version v3.6.7
connecting to: mongodb://127.0.0.1:27018/
MongoDB server version: 3.6.7

true:PRIMARY> rs.status()                  //查看复制集信息

..............

    },
    "members" : [
        {
            "_id" : 0,
           "name" : "192.168.195.137:27017",                           //原来的主节点健康值为0
            "health" : 0,
            "state" : 8,
            "stateStr" : "(not reachable/healthy)",
            "uptime" : 0,
            "optime" : {
                "ts" : Timestamp(0, 0),
                "t" : NumberLong(-1)
            },
            "optimeDurable" : {
                "ts" : Timestamp(0, 0),
                "t" : NumberLong(-1)
            },

.................

                  {
            "_id" : 1,
           "name" : "192.168.195.137:27018",
            "health" : 1,
            "state" : 1,
           "stateStr" : "PRIMARY",                         //此节点切换成主节点
            "uptime" : 2657,
            "optime" : {
                "ts" : Timestamp(1537027275, 1),
                "t" : NumberLong(2)
            },

................

                    {
            "_id" : 2,
            "name" : "192.168.195.137:27019",
            "health" : 1,
            "state" : 2,
            "stateStr" : "SECONDARY",
            "uptime" : 1312,
            "optime" : {
                "ts" : Timestamp(1537027275, 1),
                "t" : NumberLong(2)
            },
            "optimeDurable" : {
                "ts" : Timestamp(1537027275, 1),
                "t" : NumberLong(2)
            },
          

手动进行主从切换

[root@localhost ~]# mongod -f /etc/mongod.conf           #开启刚才关闭的端口为27017的节点实例

about to fork child process, waiting until server is ready for connections.
forked process: 94723
child process started successfully, parent exiting
[root@localhost ~]# mongo --port 27018             #进入主节点服务器实例
MongoDB shell version v3.6.7
connecting to: mongodb://127.0.0.1:27018/
MongoDB server version: 3.6.7

true:PRIMARY> rs.freeze(30)                     //暂停30s不参与选举

true:PRIMARY> rs.stepDown(60.30)              //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  

true:SECONDARY> rs.status()             //可以看到本实例已经切换成从节点

................

    "members" : [
        {
            "_id" : 0,
            "name" : "192.168.195.137:27017",                // 端口27017的节点变成了主节点
            "health" : 1,
            "state" : 1,
            "stateStr" : "PRIMARY",                        
            "uptime" : 167,
            "optime" : {
                "ts" : Timestamp(1537027620, 1),
                "t" : NumberLong(3)
            },
            "optimeDurable" : {
                "ts" : Timestamp(1537027620, 1),
                "t" : NumberLong(3)
            },

..................
            
        {
            "_id" : 1,
            "name" : "192.168.195.137:27018",                    // 端口27018的节点变成了从节点         

            "health" : 1,
            "state" : 2,
            "stateStr" : "SECONDARY",
            "uptime" : 2997,
            "optime" : {
                "ts" : Timestamp(1537027620, 1),
                "t" : NumberLong(3)
            },

...................
          
        {
            "_id" : 2,
            "name" : "192.168.195.137:27019",
            "health" : 1,
            "state" : 2,
            "stateStr" : "SECONDARY",
            "uptime" : 1651,
            "optime" : {
                "ts" : Timestamp(1537027620, 1),
                "t" : NumberLong(3)
            },
            "optimeDurable" : {
                "ts" : Timestamp(1537027620, 1),
                "t" : NumberLong(3)
            },