Configuring Master-Slave replication for REDIS Server - UBUNTU

Redis is an highly popular open source in memory key - value data store that is currently in use at and highly praised by tech companies such as Twitter, Stack Exchange and Git hub.

The setup of Redis was so easy that I thought it would be a good idea to share how to install and configure a Redis instance for Master - Slave replication.

What is Master - Slave Replication?

Master - Slave replication is a data replication concept seen often in the database world. This replication allows for a database service to replicate data written to the master instance to a slave instance. This slave instance could be located within the same facility for scaling out read requests or in another facility in order to mitigate a disaster recovery scenario.

In general slave servers are read only, Redis is no different; however it does have the ability to override this setting however data only written to the slave will be lost during a re synchronization to the master server. Usually a Master server can have many slave servers setup, in the case of Redis a slave server can also serve as the master server for other slaves. This configuration allows one to send all write requests to the single master server and be able to scale out any read requests against many slaves.

Setup the Master Server:

1.Install the Server

In this article we will be installing Redis on Ubuntu 13.10; we can do this using the apt package manager.

ubuntu@redis-master:~$ sudo apt-get install redis-server

2.Configuration:

Before starting Redis we will need to configure a few items within the /etc/redis/redis.conf configuration file.

ubuntu@redis-master:~$ sudo vi /etc/redis/redis.conf

3.Changing the Listening Interface:

By default Redis binds to the localhost IP, this would be fine if we were only using Redis locally. In this example however we are setting up replication and will need to change the bind address to the public IP.

Find:

bind 127.0.0.1

Replace with:

bind 

Example:

bind 10.3.x.x

4.Adding Password Authentication:

Redis does not have a concept of users and permissions that you would see with a traditional database such as MySQL, however Redis does have a simple password based authentication. To require password based authentication we will need to un-comment therequirepass setting.

Find:

# requirepass foobared

Replace with:

requirepass somesuperlongpasswordthathaslotsofspecialcharacters

5.Restart the Redis Server:

At this point after saving the configuration file we will restart the redis-server service.

ubuntu@redis-master:~$ sudo /etc/init.d/redis-server restart

6.Installation on the Slaves:

Setting up a Redis Slave is the same as setting up the master; however we will need to add a few more configuration steps.

Install the Redis Server package

ubuntu@redis-slave:~$ sudo apt-get install redis-server

7.Configuration:

We will again need to modify the Redis server configuration file.

ubuntu@redis-slave:~$ sudo vi /etc/redis/redis.conf

8.Changing the Listening Interface:

Again we will change the bind address to the public IP address of the slave server.

Find:

bind 127.0.0.1

Replace with:

bind  

9.Adding Password Authentication:

While slave systems are read only by default it is a good idea to enable password authentication to prevent clients from reading data without authenticating. This setting is optional, if you do not care about securing the data being read than this can stay commented.

Find:

# requirepass foobared

Replace with:

requirepass somesuperlongpasswordthathaslotsofspecialcharacters

10.Setting up Replication:

The below steps will outline setting up replication from the Slave. Replication only needs to be defined on Slave systems, the Master server does not require any special configuration.

11.Specifying the Master:

In the slave configuration file specify the master server to replicate from. Redis has the ability to replicate from a slave, to set this up you would simply specify the first slaves details in place of the master.

Find:

# slaveof   

Replace With:

slaveof    

Example:

slaveof 10.3.x.x 6379

12.Authentication:

If you set a password earlier for the master server you will need to specify that password via the masterauth setting.

Find:

# masterauth 

Replace With:

masterauth somesuperlongpasswordthathaslotsofspecialcharacters

13.Start the Service:

At this point we can start the redis-server on the slave.

ubuntu@redis-slave:~$ service redis-server start

14.Testing Replication:

To test the replication we will first login to the master server and set a key-value.

15.Set the key-value on the Redis Master:

To login to the Redis server we will use the redis-cli client. The -h flag specifies the host to connect to, by default the redis-cli will connect to the localhost IP.

ubuntu@redis-master:~$ redis-cli -h 10.3.x.x

Once logged in use the AUTH command with the password specified earlier.

 redis 10.3.x.x:6379>  AUTH 
 OK

After authenticating we can now set a key-value pair using the SET command.

 redis 10.3.x.x:6379>  SET replicated:test true
 OK

16.Get the key-value on the Redis Slave:

Now that data has been saved to the master we will login to the Redis Slave server using the same redis-cli command and use theGET command to retrieve the replicated data.

ubuntu@redis-slave:~$ redis-cli -h 10.3.3.251
redis 10.3.3.251:6379>  AUTH foobared
OK

Once logged in use the GET command to retrieve the value from the replicated:test key

 redis 10.3.3.251:6379> GET replicated:test
 "true"

At this point we have installed Redis on two systems and setup replication between them. If you required a third server you could repeat the Slave setup steps and either use the Master or Slave server as the source server.

For information about to enable the slaves to auto-promote themselves to master when the master goes down, you can check out Redis Sentinel Auto Promote to MASTER

Sentinel will monitor Redis instances and if they are down it will promote the slave to a master. You would need to handle redirecting writes to the new master as it does not handle that. 

At this point I believe Sentinel is still beta however according to their docs it is ready for use, keeping in mind it is still beta.