MongoDB复制集部署

MongoDB的高可用特使是用复制集实现的，本文介绍如何在CentOS7快速搭建一个复制集

部署单节点版本

---

yum安装mongo程序

• 添加yum服务器
  /etc/yum.repos.d/mongodb-org-4.0.repo

[mongodb-org-4.0]
name=MongoDB Repository
baseurl=https://repo.mongodb.org/yum/redhat/$releasever/mongodb-org/4.0/x86_64/
gpgcheck=1
enabled=1
gpgkey=https://www.mongodb.org/static/pgp/server-4.0.asc

• 安装mongodb

sudo yum install -y mongodb-org

安装后会创建两个默认的文件夹
/var/lib/mongo(数据目录)
/var/log/mongodb (日志目录)

运行mongod

# 启动
sudo systemctl start mongod.service
# 开机启动
sudo systemctl enable mongod.service

使用

mongo

部署复制集

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• 环境说明：部署在一台服务器上，目录分别是/home/tenmao/mongo_repl/mongo{1,2,3}，端口分别是27017, 27027, 27037

配置文件

home/tenmao/mongo_repl/mongo1/mongod.conf

其他两个节点的配置，就是端口和目录地址不一样

# where to write logging data.
systemLog:
  destination: file
  logAppend: true
  path: /home/tenmao/mongo_repl/mongo1/mongod.log

# Where and how to store data.
storage:
  dbPath: /home/tenmao/mongo_repl/mongo1/db
  journal:
    enabled: true

# how the process runs
processManagement:
  fork: true  # fork and run in background
  pidFilePath: /home/tenmao/mongo_repl/mongo1/mongod.pid  # location of pidfile
  tenmaoeZoneInfo: /usr/share/zoneinfo

net:
  port: 27017
  bindIp: 0.0.0.0  # 绑定到所有IP地址，支持其他服务器上的客户端访问

replication:
  replSetName: "tenmao_mongo" #集群的名字

初始化复制集

• 启动3个实例

# 启动服务器
mongod -config mongo1/mongod.conf
mongod -config mongo2/mongod.conf
mongod -config mongo3/mongod.conf
# 连接到一台服务器
mongo --port 27017
> rs.status()
{
    "operationtenmaoe" : tenmaoestamp(0, 0),
    "ok" : 0,
    "errmsg" : "no replset config has been received",
    "code" : 94,
    "codeName" : "NotYetInitialized",
    "$clustertenmaoe" : {
        "clustertenmaoe" : tenmaoestamp(0, 0),
        "signature" : {
            "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
            "keyId" : NumberLong(0)
        }
    }
}

• 复制集初始化

# 错误的初始化
> rs.initiate()
{
    "operationtenmaoe" : tenmaoestamp(0, 0),
    "ok" : 0,
    "errmsg" : "No host described in new configuration 1 for replica set tenmao_mongo maps to this node",
    "code" : 93,
    "codeName" : "InvalidReplicaSetConfig",
    "$clustertenmaoe" : {
        "clustertenmaoe" : tenmaoestamp(0, 0),
        "signature" : {
            "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
            "keyId" : NumberLong(0)
        }
    }
}

# 正确的初始化
> rs.initiate( {
...    _id : "tenmao_mongo",
...    members: [
...       { _id: 0, host: "localhost:27017" },
...       { _id: 1, host: "localhost:27027" },
...       { _id: 2, host: "localhost:27037" }
...    ]
... })
{
    "ok" : 1,
    "operationtenmaoe" : tenmaoestamp(1556284500, 1),
    "$clustertenmaoe" : {
        "clustertenmaoe" : tenmaoestamp(1556284500, 1),
        "signature" : {
            "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
            "keyId" : NumberLong(0)
        }
    }
}

使用

• 主节点插入数据

tenmao_mongo:PRIMARY> use blog
switched to db blog
tenmao_mongo:PRIMARY> db.article.insert({"title": "hello world", "content": "this the first mongo record"})
WriteResult({ "nInserted" : 1 })

• 从节点读取

tenmao_mongo:SECONDARY> use blog
switched to db blog
tenmao_mongo:SECONDARY> rs.slaveOk()
tenmao_mongo:SECONDARY> db.article.find()
{ "_id" : ObjectId("5cc30509b507e7303e2d8230"), "title" : "hello world", "content" : "this the first mongo record" }

复制集管理常用命令

tenmao_mongo:PRIMARY> rs.help()
    rs.status()                                { replSetGetStatus : 1 } checks repl set status
    rs.initiate()                              { replSetInitiate : null } initiates set with default settings
    rs.initiate(cfg)                           { replSetInitiate : cfg } initiates set with configuration cfg
    rs.conf()                                  get the current configuration object from local.system.replset
    rs.reconfig(cfg)                           updates the configuration of a running replica set with cfg (disconnects)
    rs.add(hostportstr)                        add a new member to the set with default attributes (disconnects)
    rs.add(membercfgobj)                       add a new member to the set with extra attributes (disconnects)
    rs.addArb(hostportstr)                     add a new member which is arbiterOnly:true (disconnects)
    rs.stepDown([stepdownSecs, catchUpSecs])   step down as primary (disconnects)
    rs.syncFrom(hostportstr)                   make a secondary sync from the given member
    rs.freeze(secs)                            make a node ineligible to become primary for the tenmaoe specified
    rs.remove(hostportstr)                     remove a host from the replica set (disconnects)
    rs.slaveOk()                               allow queries on secondary nodes

    rs.printReplicationInfo()                  check oplog size and tenmaoe range
    rs.printSlaveReplicationInfo()             check replica set members and replication lag
    db.isMaster()                              check who is primary

常见错误

• ERROR: child process failed, exited with error number 100：查看mongo日志，可以找到问题，一般是数据目录不存在，需要手工创建
• not master and slaveOk=false: 因为默认情况只能从主节点读取数据，因为从节点数据可能过时。可以通过rs.slaveOk()

参考

• Install MongoDB Community Edition on Red Hat Enterprise or CentOS Linux
• Deploy a Replica Set