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Complete 20150518 How to set up a Replica Set on MongoDB.md
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Translating by Ping
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How to set up a Replica Set on MongoDB
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================================================================================
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MongoDB has become the most famous NoSQL database on the market. MongoDB is document-oriented, and its scheme-free design makes it a really attractive solution for all kinds of web applications. One of the features that I like the most is Replica Set, where multiple copies of the same data set are maintained by a group of mongod nodes for redundancy and high availability.
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This tutorial describes how to configure a Replica Set on MonoDB.
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The most common configuration for a Replica Set involves one primary and multiple secondary nodes. The replication will then be initiated from the primary toward the secondaries. Replica Sets can not only provide database protection against unexpected hardware failure and service downtime, but also improve read throughput of database clients as they can be configured to read from different nodes.
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### Set up the Environment ###
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In this tutorial, we are going to set up a Replica Set with one primary and two secondary nodes.
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In order to implement this lab, we will use three virtual machines (VMs) running on VirtualBox. I am going to install Ubuntu 14.04 on the VMs, and install official packages for Mongodb.
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I am going to set up a necessary environment on one VM instance, and then clone it to the other two VM instances. Thus pick one VM named master, and perform the following installations.
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First, we need to add the MongoDB key for apt:
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$ sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 7F0CEB10
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Then we need to add the official MongoDB repository to our source.list:
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$ sudo su
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# echo "deb http://repo.mongodb.org/apt/ubuntu "$(lsb_release -sc)"/mongodb-org/3.0 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-3.0.list
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Let's update repositories and install MongoDB.
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$ sudo apt-get update
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$ sudo apt-get install -y mongodb-org
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Now let's make some changes in /etc/mongodb.conf.
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auth = true
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dbpath=/var/lib/mongodb
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logpath=/var/log/mongodb/mongod.log
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logappend=true
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keyFile=/var/lib/mongodb/keyFile
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replSet=myReplica
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The first line is to make sure that we are going to have authentication on our database. keyFile is to set up a keyfile that is going to be used by MongoDB to replicate between nodes. replSet sets up the name of our replica set.
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Now we are going to create our keyfile, so that it can be in all our instances.
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$ echo -n "MyRandomStringForReplicaSet" | md5sum > keyFile
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This will create keyfile that contains a MD5 string, but it has some noise that we need to clean up before using it in MongoDB. Use the following command to clean it up:
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$ echo -n "MyReplicaSetKey" | md5sum|grep -o "[0-9a-z]\+" > keyFile
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What grep command does is to print MD5 string with no spaces or other characters that we don't want.
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Now we are going to make the keyfile ready for use:
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$ sudo cp keyFile /var/lib/mongodb
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$ sudo chown mongodb:nogroup keyFile
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$ sudo chmod 400 keyFile
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Now we have our Ubuntu VM ready to be cloned. Power it off, and clone it to the other VMs.
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I name the cloned VMs secondary1 and secondary2. Make sure to reinitialize the MAC address of cloned VMs and clone full disks.
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All three VM instances should be on the same network to communicate with each other. For this, we are going to attach all three VMs to "Internet Network".
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It is recommended that each VM instances be assigned a static IP address, as opposed to DHCP IP address, so that the VMs will not lose connectivity among themselves when a DHCP server assigns different IP addresses to them.
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Let's edit /etc/networks/interfaces of each VM as follows.
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On primary:
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auto eth1
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iface eth1 inet static
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address 192.168.50.2
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netmask 255.255.255.0
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On secondary1:
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auto eth1
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iface eth1 inet static
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address 192.168.50.3
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netmask 255.255.255.0
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On secondary2:
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auto eth1
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iface eth1 inet static
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address 192.168.50.4
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netmask 255.255.255.0
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Another file that needs to be set up is /etc/hosts, because we don't have DNS. We need to set the hostnames in /etc/hosts.
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On primary:
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127.0.0.1 localhost primary
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192.168.50.2 primary
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192.168.50.3 secondary1
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192.168.50.4 secondary2
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On secondary1:
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127.0.0.1 localhost secondary1
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192.168.50.2 primary
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192.168.50.3 secondary1
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192.168.50.4 secondary2
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On secondary2:
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127.0.0.1 localhost secondary2
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192.168.50.2 primary
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192.168.50.3 secondary1
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192.168.50.4 secondary2
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Check connectivity among themselves by using ping command:
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$ ping primary
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$ ping secondary1
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$ ping secondary2
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### Set up a Replica Set ###
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After verifying connectivity among VMs, we can go ahead and create the admin user so that we can start working on the Replica Set.
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On primary node, open /etc/mongodb.conf, and comment out two lines that start with auth and replSet:
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dbpath=/var/lib/mongodb
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logpath=/var/log/mongodb/mongod.log
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logappend=true
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#auth = true
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keyFile=/var/lib/mongodb/keyFile
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#replSet=myReplica
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Restart mongod daemon.
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$ sudo service mongod restart
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Create an admin user after conencting to MongoDB:
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> use admin
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> db.createUser({
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user:"admin",
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pwd:"
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})
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$ sudo service mongod restart
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Connect to MongoDB and use these commands to add secondary1 and secondary2 to our Replicat Set.
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> use admin
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> db.auth("admin","myreallyhardpassword")
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> rs.initiate()
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> rs.add ("secondary1:27017")
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> rs.add("secondary2:27017")
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Now that we have our Replica Set, we can start working on our project. Consult the [official driver documentation][1] to see how to connect to a Replica Set. In case you want to query from shell, you have to connect to primary instance to insert or query the database. Secondary nodes will not let you do that. If you attempt to access the database on a secondary node, you will get this error message:
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myReplica:SECONDARY>
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myReplica:SECONDARY> show databases
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2015-05-10T03:09:24.131+0000 E QUERY Error: listDatabases failed:{ "note" : "from execCommand", "ok" : 0, "errmsg" : "not master" }
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at Error ()
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at Mongo.getDBs (src/mongo/shell/mongo.js:47:15)
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at shellHelper.show (src/mongo/shell/utils.js:630:33)
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at shellHelper (src/mongo/shell/utils.js:524:36)
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at (shellhelp2):1:1 at src/mongo/shell/mongo.js:47
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I hope you find this tutorial useful. You can use Vagrant to automate your local environments and help you code faster.
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--------------------------------------------------------------------------------
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via: http://xmodulo.com/setup-replica-set-mongodb.html
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作者：[Christopher Valerio][a]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创翻译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]:http://xmodulo.com/author/valerio
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[1]:http://docs.mongodb.org/ecosystem/drivers/
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如何配置MongoDB副本集（Replica Set）
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================================================================================
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MongoDB已经成为市面上最知名的NoSQL数据库。MongoDB是面向文档的，它的无模式设计使得它在各种各样的WEB应用当中广受欢迎。最让我喜欢的特性之一是它的副本集，副本集将同一数据的多份拷贝放在一组mongod节点上，从而实现数据的冗余以及高可用性。
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这篇教程将向你介绍如何配置一个MongoDB副本集。
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副本集的最常见配置涉及到一个主节点以及多个副节点。这之后启动的复制行为会从这个主节点到其他副节点。副本集不止可以针对意外的硬件故障和停机事件对数据库提供保护，同时也因为提供了更多的结点从而提高了数据库客户端数据读取的吞吐量。
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### 配置环境 ###
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这个教程里，我们会配置一个包括一个主节点以及两个副节点的副本集。
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为了达到这个目的，我们使用了3个运行在VirtualBox上的虚拟机。我会在这些虚拟机上安装Ubuntu 14.04，并且安装MongoDB官方包。
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我会在一个虚拟机实例上配置好需要的环境，然后将它克隆到其他的虚拟机实例上。因此，选择一个名为master的虚拟机，执行以下安装过程。
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首先，我们需要在apt中增加一个MongoDB密钥：
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$ sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 7F0CEB10
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然后，将官方的MongoDB仓库添加到source.list中：
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$ sudo su
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# echo "deb http://repo.mongodb.org/apt/ubuntu "$(lsb_release -sc)"/mongodb-org/3.0 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-3.0.list
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接下来更新apt仓库并且安装MongoDB。
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$ sudo apt-get update
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$ sudo apt-get install -y mongodb-org
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现在对/etc/mongodb.conf做一些更改
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auth = true
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dbpath=/var/lib/mongodb
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logpath=/var/log/mongodb/mongod.log
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logappend=true
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keyFile=/var/lib/mongodb/keyFile
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replSet=myReplica
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第一行的作用是确认我们的数据库需要验证才可以使用的。keyfile用来配置用于MongoDB结点间复制行为的密钥文件。replSet用来为副本集设置一个名称。
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接下来我们创建一个用于所有实例的密钥文件。
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$ echo -n "MyRandomStringForReplicaSet" | md5sum > keyFile
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这将会创建一个含有MD5字符串的密钥文件，但是由于其中包含了一些噪音，我们需要对他们清理后才能正式在MongoDB中使用。
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$ echo -n "MyReplicaSetKey" | md5sum|grep -o "[0-9a-z]\+" > keyFile
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grep命令的作用的是把将空格等我们不想要的内容过滤掉之后的MD5字符串打印出来。
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现在我们对密钥文件进行一些操作，让它真正可用。
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$ sudo cp keyFile /var/lib/mongodb
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$ sudo chown mongodb:nogroup keyFile
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$ sudo chmod 400 keyFile
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接下来，关闭此虚拟机。将其Ubuntu系统克隆到其他虚拟机上。
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这是克隆后的副节点1和副节点2。确认你已经将它们的MAC地址重新初始化，并且克隆整个硬盘。
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请注意，三个虚拟机示例需要在同一个网络中以便相互通讯。因此，我们需要它们弄到“互联网"上去。
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这里推荐给每个虚拟机设置一个静态IP地址，而不是使用DHCP。这样它们就不至于在DHCP分配IP地址给他们的时候失去连接。
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像下面这样编辑每个虚拟机的/etc/networks/interfaces文件。
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在主结点上:
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auto eth1
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iface eth1 inet static
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address 192.168.50.2
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netmask 255.255.255.0
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在副结点1上:
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auto eth1
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iface eth1 inet static
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address 192.168.50.3
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netmask 255.255.255.0
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在副结点2上:
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auto eth1
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iface eth1 inet static
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address 192.168.50.4
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netmask 255.255.255.0
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由于我们没有DNS服务，所以需要设置设置一下/etc/hosts这个文件，手工将主机名称放到次文件中。
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在主结点上:
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127.0.0.1 localhost primary
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192.168.50.2 primary
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192.168.50.3 secondary1
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192.168.50.4 secondary2
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在副结点1上:
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127.0.0.1 localhost secondary1
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192.168.50.2 primary
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192.168.50.3 secondary1
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192.168.50.4 secondary2
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在副结点2上:
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127.0.0.1 localhost secondary2
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192.168.50.2 primary
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192.168.50.3 secondary1
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192.168.50.4 secondary2
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使用ping命令检查各个结点之间的连接。
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$ ping primary
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$ ping secondary1
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$ ping secondary2
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### 配置副本集 ###
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验证各个结点可以正常连通后，我们就可以新建一个管理员用户，用于之后的副本集操作。
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在主节点上，打开/etc/mongodb.conf文件，将auth和replSet两项注释掉。
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dbpath=/var/lib/mongodb
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logpath=/var/log/mongodb/mongod.log
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logappend=true
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#auth = true
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keyFile=/var/lib/mongodb/keyFile
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#replSet=myReplica
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重启mongod进程。
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$ sudo service mongod restart
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连接MongoDB后，新建管理员用户。
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> use admin
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> db.createUser({
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user:"admin",
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pwd:"
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})
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$ sudo service mongod restart
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连接到MongoDB，用以下命令将secondary1和secondary2节点添加到我们的副本集中。
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> use admin
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> db.auth("admin","myreallyhardpassword")
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> rs.initiate()
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> rs.add ("secondary1:27017")
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> rs.add("secondary2:27017")
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现在副本集到手了，可以开始我们的项目了。参照 [official driver documentation][1] 来了解如何连接到副本集。如果你想要用Shell来请求数据，那么你需要连接到主节点上来插入或者请求数据，副节点不行。如果你执意要尝试用附件点操作，那么以下错误信息就蹦出来招呼你了。
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myReplica:SECONDARY>
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myReplica:SECONDARY> show databases
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2015-05-10T03:09:24.131+0000 E QUERY Error: listDatabases failed:{ "note" : "from execCommand", "ok" : 0, "errmsg" : "not master" }
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at Error ()
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at Mongo.getDBs (src/mongo/shell/mongo.js:47:15)
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at shellHelper.show (src/mongo/shell/utils.js:630:33)
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at shellHelper (src/mongo/shell/utils.js:524:36)
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at (shellhelp2):1:1 at src/mongo/shell/mongo.js:47
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希望这篇教程能对你有所帮助。你可以使用Vagrant来自动完成你的本地环境配置，并且加速你的代码。
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--------------------------------------------------------------------------------
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via: http://xmodulo.com/setup-replica-set-mongodb.html
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作者：[Christopher Valerio][a]
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译者：[mr-ping](https://github.com/mr-ping)
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校对：[校对者ID](https://github.com/校对者ID)
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||||
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||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创翻译，[Linux中国](https://linux.cn/) 荣誉推出
|
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||||
[a]:http://xmodulo.com/author/valerio
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[1]:http://docs.mongodb.org/ecosystem/drivers/
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