MongoDB 是一个基于分布式文件存储的数据库。由 C++ 语言编写。旨在为 WEB 应用提供可扩展的高性能数据存储解决方案。
MongoDB 是一个介于关系数据库和非关系数据库之间的产品，是非关系数据库当中功能最丰富，最像关系数据库的。

安装

1. 在两台服务器上安装MongoDB并配置成复制集合

1.1 创建yum repo文件(node1, node2)

# vim /etc/yum.repos.d/mongodb-org-3.4.repo

[mongodb-org-3.4]
name=MongoDB Repository
baseurl=https://repo.mongodb.org/yum/redhat/$releasever/mongodb-org/3.4/x86_64/
gpgcheck=1
enabled=1
gpgkey=https://www.mongodb.org/static/pgp/server-3.4.asc

1.2 安装MongoDB packages(node1, node2)

# sudo yum install -y mongodb-org

1.3 配置SELinux(node1, node2)

有3种选择：

• 如果SELinux处于enforcing模式：

  # mongodb的端口号为27017的情况，请根据实际情况修改
  semanage port -a -t mongod_port_t -p tcp 27017

• 关闭SELinux：

  # vim /etc/selinux/config
  SELINUX=disabled

• 设置SELinux处于permissive 模式：

  # vim /etc/selinux/config
  SELINUX=permissive

1.4 配置MongoDB(node1, node2)

# vim /etc/mongod.conf

systemLog:
  destination: file
  logAppend: true
  path: /var/log/mongodb/mongod.log

storage:
  dbPath: /var/lib/mongo
  journal:
    enabled: true

processManagement:
  fork: true  # fork and run in background
  pidFilePath: /var/run/mongodb/mongod.pid  # location of pidfile

net:
  # 按照自己的需求修改
  port: 27017

operationProfiling:
   slowOpThresholdMs: 200
   mode: slowOp

replication:
   oplogSizeMB: 2048
   replSetName: catalog

1.5 启动MongoDB服务

systemctl restart mongod

1.6 初始化MongoDB(node1)

先来看一下初始化用的config，进入db终端后拷贝输入即可。

config ={
    "_id" : "catalog",
    "members": [
        {
            "_id": 0,
            "host" : "node1:27017"
        },
        {
            "_id": 1,
            "host" : "node2:27018"
        }
    ]
    }

此处的27017和27018是对应配置文件中指定的端口号，node1和node2需要修改成自己的服务器的host名或ip。
"_id" : "catalog"中的catalog是配置文件中replSetName的值。

进入MongoDB操作命令行,依次输入：

• config = {…}
• rs.initiate(config)

• rs.status()

  # mongo -host 127.0.0.1 -port <配置文件指定的port>
  MongoDB shell version v3.4.9
  connecting to: mongodb://127.0.0.1:27017
  MongoDB server version: 3.4.9
  Server has startup warnings: 
  2017-10-20T17:58:46.781+0800 I CONTROL  [initandlisten] 
  2017-10-20T17:58:46.781+0800 I CONTROL  [initandlisten] ** WARNING: Access control is not enabled for the database.
  2017-10-20T17:58:46.781+0800 I CONTROL  [initandlisten] **          Read and write access to data and configuration is unrestricted.
  2017-10-20T17:58:46.781+0800 I CONTROL  [initandlisten] 
  2017-10-20T17:58:46.781+0800 I CONTROL  [initandlisten] 
  2017-10-20T17:58:46.781+0800 I CONTROL  [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/enabled is 'always'.
  2017-10-20T17:58:46.781+0800 I CONTROL  [initandlisten] **        We suggest setting it to 'never'
  2017-10-20T17:58:46.781+0800 I CONTROL  [initandlisten] 
  2017-10-20T17:58:46.781+0800 I CONTROL  [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/defrag is 'always'.
  2017-10-20T17:58:46.781+0800 I CONTROL  [initandlisten] **        We suggest setting it to 'never'
  2017-10-20T17:58:46.781+0800 I CONTROL  [initandlisten] 
  > 
  > 
  > 
  > config ={
  ...     "_id" : "catalog",
  ...     "members": [
  ...         {
  ...             "_id": 0,
  ...             "host" : "node1:27017"
  ...         },
  ...         {
  ...             "_id": 1,
  ...             "host" : "node2:27017"
  ...         }
  ...     ]
  ... }
  {
    "_id" : "catalog",
    "members" : [
        {
            "_id" : 0,
            "host" : "node1:27017"
        },
        {
            "_id" : 1,
            "host" : "node2:27017"
        }
    ]
  }
  > 
  > rs.initiate(config)
  {
        "info" : "Config now saved locally.  Should come online in about a minute.",  
        "ok" : 1
  }
  >   
  catalog:PRIMARY> 
  catalog:PRIMARY> 
  catalog:PRIMARY>
  catalog:PRIMARY> rs.status()
  {
    "set" : "catalog",
    "date" : ISODate("2017-10-20T10:20:53.549Z"),
    "myState" : 1,
    "term" : NumberLong(4),
    "heartbeatIntervalMillis" : NumberLong(2000),
    "optimes" : {
        "lastCommittedOpTime" : {
            "ts" : Timestamp(1508494845, 1),
            "t" : NumberLong(4)
        },
        "appliedOpTime" : {
            "ts" : Timestamp(1508494845, 1),
            "t" : NumberLong(4)
        },
        "durableOpTime" : {
            "ts" : Timestamp(1508494845, 1),
            "t" : NumberLong(4)
        }
    },
    "members" : [
        {
            "_id" : 0,
            "name" : "node1:27017",
            "health" : 1,
            "state" : 1,
            "stateStr" : "PRIMARY",
            "uptime" : 1327,
            "optime" : {
                "ts" : Timestamp(1508494845, 1),
                "t" : NumberLong(4)
            },
            "optimeDate" : ISODate("2017-10-20T10:20:45Z"),
            "electionTime" : Timestamp(1508493663, 1),
            "electionDate" : ISODate("2017-10-20T10:01:03Z"),
            "configVersion" : 1,
            "self" : true
        },
        {
            "_id" : 1,
            "name" : "node2:27018",
            "health" : 1,
            "state" : 2,
            "stateStr" : "SECONDARY",
            "uptime" : 1196,
            "optime" : {
                "ts" : Timestamp(1508494845, 1),
                "t" : NumberLong(4)
            },
            "optimeDurable" : {
                "ts" : Timestamp(1508494845, 1),
                "t" : NumberLong(4)
            },
            "optimeDate" : ISODate("2017-10-20T10:20:45Z"),
            "optimeDurableDate" : ISODate("2017-10-20T10:20:45Z"),
            "lastHeartbeat" : ISODate("2017-10-20T10:20:51.727Z"),
            "lastHeartbeatRecv" : ISODate("2017-10-20T10:20:52.810Z"),
            "pingMs" : NumberLong(0),
            "syncingTo" : "node1:27017",
            "configVersion" : 1
        }
    ],
    "ok" : 1
    }

  可以通过rs.add(host:port)来增加member，rs.remove(host:port)来删除member