Review

In the previous section, we have introduced and discussed Replica Sets. In this section, we will install MongoDB and configure Replica Sets.

Part 1: Introduction
Part 2: Installation and configuration of Replica Sets
Part 3: Spring app configuration
Part 4: Testing the servers

Installation

Our first step is to download and install MongoDB in each server. Since our server is running CentOS, we can download the CentOS MongoDB package by following the instructions from this link. However, it is easier to simply install the prebuilt binaries as stated in the MongoDB downloads section, so we will follow this advice instead.

1. Open a browser and visit the MongoDB download section at http://www.mongodb.org/downloads

2. Under the Production Release, choose the file that matches your operating system. In our case, it's Linux 32-bit.

3. Once downloaded, transfer the compressed file to all servers. (In each server, we have created a directory named /home/mongo. This is where we will extract the contents of the compressed file.)

4. Extract the contents by running the following command (you might need to modify the directory). Remember to do these on all servers.

tar -C /home/mongo/ -zxvf/home/mongo/mongodb-linux-i686-2.0.2.tgz

5. Now we need to create the database directory for our MongoDB servers. By default, /data/db is used by MongoDB, so we'll create those directories by running the following command (Remember to do these on all servers):

mkdir -p/data/db

6. Next, we will run MongoDB servers in a Replica Set using the following command (Again, do these step on all servers):

/home/mongo/mongodb-linux-i686-2.0.2/bin/./mongod --replSet cluster1

Server 1 should output the following log:

[Server #1] /home/mongo/mongodb-linux-i686-2.0.2/bin/./mongod --replSet cluster1
Sat Feb 18 11:14:36 
Sat Feb 18 11:14:36 warning: 32-bit servers don't have journaling enabled by default. Please use --journal if you want durability.
Sat Feb 18 11:14:36 
Sat Feb 18 11:14:36 [initandlisten] MongoDB starting : pid=5921 port=27017 dbpath=/data/db/ 32-bit host=28125_2_85413_357231
Sat Feb 18 11:14:36 [initandlisten] 
Sat Feb 18 11:14:36 [initandlisten] ** NOTE: when using MongoDB 32 bit, you are limited to about 2 gigabytes of data
Sat Feb 18 11:14:36 [initandlisten] **       see http://blog.mongodb.org/post/137788967/32-bit-limitations
Sat Feb 18 11:14:36 [initandlisten] **       with --journal, the limit is lower
Sat Feb 18 11:14:36 [initandlisten] 
Sat Feb 18 11:14:36 [initandlisten] db version v2.0.2, pdfile version 4.5
Sat Feb 18 11:14:36 [initandlisten] git version: 514b122d308928517f5841888ceaa4246a7f18e3
Sat Feb 18 11:14:36 [initandlisten] build info: Linux domU-12-31-39-01-70-B4 2.6.21.7-2.fc8xen #1 SMP Fri Feb 15 12:39:36 EST 2008 i686 BOOST_LIB_VERSION=1_41
Sat Feb 18 11:14:36 [initandlisten] options: { replSet: "cluster1" }
Sat Feb 18 11:14:36 [initandlisten] waiting for connections on port 27017
Sat Feb 18 11:14:36 [websvr] admin web console waiting for connections on port 28017
Sat Feb 18 11:14:36 [initandlisten] connection accepted from 127.0.0.1:39621 #1
Sat Feb 18 11:14:36 [rsStart] replSet can't get local.system.replset config from self or any seed (EMPTYCONFIG)
Sat Feb 18 11:14:36 [rsStart] replSet info you may need to run replSetInitiate -- rs.initiate() in the shell -- if that is not already done
Sat Feb 18 11:14:46 [rsStart] replSet can't get local.system.replset config from self or any seed (EMPTYCONFIG)
Sat Feb 18 11:14:56 [rsStart] replSet can't get local.system.replset config from self or any seed (EMPTYCONFIG)

Server 2 should output the following log:

[Server #2] /home/mongo/mongodb-linux-i686-2.0.2/bin/./mongod --replSet cluster1
Sat Feb 18 11:15:34 
Sat Feb 18 11:15:34 warning: 32-bit servers don't have journaling enabled by default. Please use --journal if you want durability.
Sat Feb 18 11:15:34 
Sat Feb 18 11:15:34 [initandlisten] MongoDB starting : pid=13534 port=27017 dbpath=/data/db/ 32-bit host=28125_2_82937_349828
Sat Feb 18 11:15:34 [initandlisten] 
Sat Feb 18 11:15:34 [initandlisten] ** NOTE: when using MongoDB 32 bit, you are limited to about 2 gigabytes of data
Sat Feb 18 11:15:34 [initandlisten] **       see http://blog.mongodb.org/post/137788967/32-bit-limitations
Sat Feb 18 11:15:34 [initandlisten] **       with --journal, the limit is lower
Sat Feb 18 11:15:34 [initandlisten] 
Sat Feb 18 11:15:34 [initandlisten] db version v2.0.2, pdfile version 4.5
Sat Feb 18 11:15:34 [initandlisten] git version: 514b122d308928517f5841888ceaa4246a7f18e3
Sat Feb 18 11:15:34 [initandlisten] build info: Linux domU-12-31-39-01-70-B4 2.6.21.7-2.fc8xen #1 SMP Fri Feb 15 12:39:36 EST 2008 i686 BOOST_LIB_VERSION=1_41
Sat Feb 18 11:15:34 [initandlisten] options: { replSet: "cluster1" }
Sat Feb 18 11:15:34 [initandlisten] waiting for connections on port 27017
Sat Feb 18 11:15:34 [websvr] admin web console waiting for connections on port 28017
Sat Feb 18 11:15:34 [initandlisten] connection accepted from 127.0.0.1:46620 #1
Sat Feb 18 11:15:34 [rsStart] replSet can't get local.system.replset config from self or any seed (EMPTYCONFIG)
Sat Feb 18 11:15:34 [rsStart] replSet info you may need to run replSetInitiate -- rs.initiate() in the shell -- if that is not already done
Sat Feb 18 11:15:44 [rsStart] replSet can't get local.system.replset config from self or any seed (EMPTYCONFIG)

Server 3 should output the following log:

[Server #3] /home/mongo/mongodb-linux-i686-2.0.2/bin/./mongod --replSet cluster1
Sat Feb 18 11:15:35 
Sat Feb 18 11:15:35 warning: 32-bit servers don't have journaling enabled by default. Please use --journal if you want durability.
Sat Feb 18 11:15:35 
Sat Feb 18 11:15:35 [initandlisten] MongoDB starting : pid=8902 port=27017 dbpath=/data/db/ 32-bit host=28125_2_85413_357219
Sat Feb 18 11:15:35 [initandlisten] 
Sat Feb 18 11:15:35 [initandlisten] ** NOTE: when using MongoDB 32 bit, you are limited to about 2 gigabytes of data
Sat Feb 18 11:15:35 [initandlisten] **       see http://blog.mongodb.org/post/137788967/32-bit-limitations
Sat Feb 18 11:15:35 [initandlisten] **       with --journal, the limit is lower
Sat Feb 18 11:15:35 [initandlisten] 
Sat Feb 18 11:15:35 [initandlisten] db version v2.0.2, pdfile version 4.5
Sat Feb 18 11:15:35 [initandlisten] git version: 514b122d308928517f5841888ceaa4246a7f18e3
Sat Feb 18 11:15:35 [initandlisten] build info: Linux domU-12-31-39-01-70-B4 2.6.21.7-2.fc8xen #1 SMP Fri Feb 15 12:39:36 EST 2008 i686 BOOST_LIB_VERSION=1_41
Sat Feb 18 11:15:35 [initandlisten] options: { replSet: "cluster1" }
Sat Feb 18 11:15:35 [initandlisten] waiting for connections on port 27017
Sat Feb 18 11:15:35 [websvr] admin web console waiting for connections on port 28017
Sat Feb 18 11:15:35 [initandlisten] connection accepted from 127.0.0.1:52051 #1
Sat Feb 18 11:15:35 [rsStart] replSet can't get local.system.replset config from self or any seed (EMPTYCONFIG)
Sat Feb 18 11:15:35 [rsStart] replSet info you may need to run replSetInitiate -- rs.initiate() in the shell -- if that is not already done
Sat Feb 18 11:15:45 [rsStart] replSet can't get local.system.replset config from self or any seed (EMPTYCONFIG)
Sat Feb 18 11:15:55 [rsStart] replSet can't get local.system.replset config from self or any seed (EMPTYCONFIG)

Server 4 should output the following log:

[Server #4] /home/mongo/mongodb-linux-i686-2.0.2/bin/./mongod --replSet cluster1
Sat Feb 18 11:15:37 
Sat Feb 18 11:15:37 warning: 32-bit servers don't have journaling enabled by default. Please use --journal if you want durability.
Sat Feb 18 11:15:37 
Sat Feb 18 11:15:37 [initandlisten] MongoDB starting : pid=11685 port=27017 dbpath=/data/db/ 32-bit host=28125_2_84690_354582
Sat Feb 18 11:15:37 [initandlisten] 
Sat Feb 18 11:15:37 [initandlisten] ** NOTE: when using MongoDB 32 bit, you are limited to about 2 gigabytes of data
Sat Feb 18 11:15:37 [initandlisten] **       see http://blog.mongodb.org/post/137788967/32-bit-limitations
Sat Feb 18 11:15:37 [initandlisten] **       with --journal, the limit is lower
Sat Feb 18 11:15:37 [initandlisten] 
Sat Feb 18 11:15:37 [initandlisten] db version v2.0.2, pdfile version 4.5
Sat Feb 18 11:15:37 [initandlisten] git version: 514b122d308928517f5841888ceaa4246a7f18e3
Sat Feb 18 11:15:37 [initandlisten] build info: Linux domU-12-31-39-01-70-B4 2.6.21.7-2.fc8xen #1 SMP Fri Feb 15 12:39:36 EST 2008 i686 BOOST_LIB_VERSION=1_41
Sat Feb 18 11:15:37 [initandlisten] options: { replSet: "cluster1" }
Sat Feb 18 11:15:37 [initandlisten] waiting for connections on port 27017
Sat Feb 18 11:15:37 [websvr] admin web console waiting for connections on port 28017
Sat Feb 18 11:15:37 [initandlisten] connection accepted from 127.0.0.1:51100 #1
Sat Feb 18 11:15:37 [rsStart] replSet can't get local.system.replset config from self or any seed (EMPTYCONFIG)
Sat Feb 18 11:15:37 [rsStart] replSet info you may need to run replSetInitiate -- rs.initiate() in the shell -- if that is not already done
Sat Feb 18 11:15:47 [rsStart] replSet can't get local.system.replset config from self or any seed (EMPTYCONFIG)
Sat Feb 18 11:15:57 [rsStart] replSet can't get local.system.replset config from self or any seed (EMPTYCONFIG)

7. Next step is to configure our MongoDB servers to act as a cluster. Follow the steps below:

Run a MongoDB client using the following command:

/home/mongo/mongodb-linux-i686-2.0.2/bin/./mongo

Initiate the MongoDB cluster

rs.initiate({_id: 'cluster1', members: [
 {_id: 0, host: '123.456.78.90:27017'},
 {_id: 1, host: '123.456.78.91:27017'},
 {_id: 2, host: '123.456.78.92:27017'},
 {_id: 3, host: '123.456.78.93:27017', arbiterOnly: true}]
})

If you have accidentally initiated an incorrect configuration, you can reconfigure the configuration with:

rs.reconfig({_id: 'cluster1', members: [
 {_id: 0, host: '123.456.78.90:27017'},
 {_id: 1, host: '123.456.78.91:27017'},
 {_id: 2, host: '123.456.78.92:27017'},
 {_id: 3, host: '123.456.78.93:27017', arbiterOnly: true}]
}, true)

Notice, the last host is an arbiter only server. This will participate in electing a primary but receive no data.

You should see the following output from MongoDB client:

> rs.initiate({_id: 'cluster1', members: [
bye
[Server #1] /home/mongo/mongodb-linux-i686-2.0.2/bin/./mongo
MongoDB shell version: 2.0.2
connecting to: test
> rs.initiate({_id: 'cluster1', members: [
... {_id: 0, host: '123.456.78.90:27017'},
... {_id: 1, host: '123.456.78.91:27017'},
... {_id: 2, host: '123.456.78.92:27017'},
... {_id: 3, host: '123.456.78.93:27017', arbiterOnly: true}]
... })
{
"info" : "Config now saved locally.  Should come online in about a minute.",
"ok" : 1
}

Examine the output from Server 1

Sat Feb 18 11:16:22 [conn2] replSet replSetInitiate admin command received from client
Sat Feb 18 11:16:22 [conn2] replSet replSetInitiate config object parses ok, 4 members specified
Sat Feb 18 11:16:22 [conn2] replSet replSetInitiate all members seem up
Sat Feb 18 11:16:22 [conn2] ******
Sat Feb 18 11:16:22 [conn2] creating replication oplog of size: 47MB...
Sat Feb 18 11:16:22 [FileAllocator] allocating new datafile /data/db/local.ns, filling with zeroes...
Sat Feb 18 11:16:22 [FileAllocator] creating directory /data/db/_tmp
Sat Feb 18 11:16:22 [FileAllocator] done allocating datafile /data/db/local.ns, size: 16MB,  took 0.053 secs
Sat Feb 18 11:16:22 [FileAllocator] allocating new datafile /data/db/local.0, filling with zeroes...
Sat Feb 18 11:16:22 [FileAllocator] done allocating datafile /data/db/local.0, size: 16MB,  took 0.106 secs
Sat Feb 18 11:16:22 [FileAllocator] allocating new datafile /data/db/local.1, filling with zeroes...
Sat Feb 18 11:16:23 [FileAllocator] done allocating datafile /data/db/local.1, size: 32MB,  took 1.124 secs
Sat Feb 18 11:16:23 [FileAllocator] allocating new datafile /data/db/local.2, filling with zeroes...
Sat Feb 18 11:16:26 [FileAllocator] done allocating datafile /data/db/local.2, size: 64MB,  took 3.228 secs
Sat Feb 18 11:16:29 [conn2] ******
Sat Feb 18 11:16:29 [rsStart] replSet can't get local.system.replset config from self or any seed (EMPTYCONFIG)
Sat Feb 18 11:16:29 [conn2] replSet info saving a newer config version to local.system.replset
Sat Feb 18 11:16:29 [conn2] replSet saveConfigLocally done
Sat Feb 18 11:16:29 [conn2] replSet replSetInitiate config now saved locally.  Should come online in about a minute.
Sat Feb 18 11:16:29 [conn2] command admin.$cmd command: { replSetInitiate: { _id: "cluster1", members: [ { _id: 0.0, host: "123.456.78.90:27017" }, { _id: 1.0, host: "123.456.78.91:27017" }, { _id: 2.0, host: "123.456.78.92:27017" }, { _id: 3.0, host: "123.456.78.93:27017", arbiterOnly: true } ] } } ntoreturn:1 reslen:112 7192ms
Sat Feb 18 11:16:39 [rsStart] replSet STARTUP2
Sat Feb 18 11:16:39 [rsHealthPoll] replSet member 123.456.78.91:27017 is up
Sat Feb 18 11:16:39 [rsHealthPoll] replSet member 123.456.78.92:27017 is up
Sat Feb 18 11:16:39 [rsHealthPoll] replSet member 123.456.78.93:27017 is up

In the next section, we will configure our Spring application to support Replica Sets. Click here to proceed.

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