Configuring MongoDB HA Replica Set on AWS EC2

Background

It has always been a tedious task to choose the right configuration for

MongoDB on AWS EC2

Choosing the right configuration in this environment is always challenging

and it takes a lots of time to make your system Production Ready.

What does it take?

All it needs is two machines that will be used as PRIMARY (Master)

and SECONDARY (Slave) node and one ARBITER machine for the

replica set.

However, it might get changed based on your application

requirement and you can opt for higher number of nodes based on

your need

ARBITER is only required in case of even number replica set. If you

want to maintain replica set with one PRIMARY and two SECONDARY,

ARBITER is not required

Hardware Requirement

Two 64 bit EC2 instances of medium/large or higher configuration

based on your App requirement for PRIMARY and SECONDARY node

(There is a data storage limitation of using 32 bit machine and can only

support upto 2.5 GB storage)

A small 32 bit EC2 machine for MongoDB ARBITER

It is recommended –

• to have machines in different availability zone to make it High

available in-case of a shutdown of one availability zone

• to use Ext4 EBS volume to support I/O suspend and write-cache

flushing for multi-disk consistent snapshots

Installation Steps

Create and Launch an EC2 instance of required configuration as

stated above for PRIMARY, SECONDARY and ARBITER nodes

Create an EBS volume of required size to be used for MongoDB storage

for both nodes

Connect to EC2 instances on PRIMARY and SECONDARY node via SSH

Make an Ext4 file system on both nodes via sudo mkfs -t ext4

/dev/<Created EBS Volume>

Create directory /data/db or any other of your own choice and mount

it to attached volume using sudo mount -a /dev/< Created EBS

Volume > /data/db

Contd..

Edit your /etc/fstab to enumerate it on start up of instance using

sudo echo ‘/dev/sdf /data/db auto noatime,noexec,nodiratime 0 0’

>> /etc/fstab

Download and Install MongoDB on all instances

Start the PRIMARY node with following command in MongoDB

directory using mongod --rest --replSet myHASet (where myHASet is

the name of Replica set; you can choose any name of your choice)

Go to Mongo terminal in MongoDB directory.

Initialize the set using command rs.initiate() on mongo terminal

Check the status of Replica set after initialization using rs.status()

command.

If initialization is success you will see OK in the output something like

this

{

"set" : "sample",

"myState" : 1,

"members" : [

{

"name" : "<PRIMARY_HOSTNAME>:27017",

"self" : true

}

],

"ok" : 1

}

You can also check the status on

http://<PRIMARY_NODE>:27017/_replSet

Your Primary node is ready to use now. You can insert/update document

on this node

Contd..

Now start the SECONDARY node with same command as on primary

mongod --rest --replSet myHASet

Tell the PRIMARY node to add SECONDARY node in replica set. Go to

mongo console on PRIMARY node and add this using

rs.add(“<SECONDARY_HOSTNAME>”);

If addition is successful you will see the response

Once your SECONDARY node is attached to replica set you can check

the status on http://<PRIMARY_NODE>:27017/_replSet

Now start the ARBITER node using mongod --rest --replSet myset --

oplogSize 8

Contd..

Add the ARBITER node in replica set using command rs.add( {

_id:2, host:”<ARBITER_HOSTNAME>”, arbiterOnly:true } )

Once ARBITER is added successfully, you are done with the

configuration and your replica set is ready to use.

Got o http://<PRIMARY_NODE>:27017/_replSet and you should

be able to see the status of each node.

To test the replica, take down the primary node, and see if

SECONDARY is able to pick up and will become PRIMARY node.

You can fire the command db.isMaster() to check the status if

SECONDARY node has turned up as Master node.

Contd..

Connecting Replica

• After you have setup the replica set successfully, you can connect with it

using JAVA driver from your client application

• You can use the following code snippet for making connection to replica set

• MongoDB driver is smart enough to connect to PRIMARY node only, in-case if

PRIMARY node is down, it will automatically switch to another node for

communication

List addrs = new ArrayList();

addrs.add( new ServerAddress(“<PRIMARY_HOST>",”<MONGO_PORT>" ) );

addrs.add( new ServerAddress(“<SECONDARY_HOST>",“<MONGO_PORT>"));

Mongo m = new Mongo(addrs);

DB db = m.getDB(“<NAME_OF_DB>");

Conclusion

Here is an honest attempt to guide you to setup MongoDB on AWS

EC2. Though this is an open forum and you all are open to post your

comments if I have missed anything

Also, if you don’t want to get into setting up the infrastructure and

administration for MongoDB, you can directly use our App42 NoSQL

Cloud Storage Service.

This service can be accessed using our REST API or using native

platform SDKs available in different languages like iOS, Android,

J2ME, JAVA, PHP, Ruby, Windows Phone and C#

Links for Reference :http://www.shephertz.com

http://api.shephertz.com

http://appwarp.shephertz.com

http://app42paas.shephertz.com/

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