Install Redis On Centos

Install Redis on CentOS 6.4

We’re provisioning production machines today!

This means that I’m finding a lot of things that I did previously to make my life easier. We use Redis primarily to temporarily cache data retrieved from Riak and this dramatically reduces that amount of stress on our Riak cluster.

Unfortunately, Redis doesn’t (by default) have its own package in yum.

The Hard Way

Like most freely distributed software, the process is pretty much the same: download, extract and compile.

This is what that looks like:

wget http://redis.googlecode.com/files/redis-2.6.13.tar.gz
tar xzf redis-2.6.13.tar.gz
cd redis-2.6.13
make

Unfortunately that keeps the binaries in /usr/local/bin and doesn’t include a init script (boo).

The Easy Way

Fortunately, there’s the REMI repository which packages common programs and distributes them. Let’s see what it looks like with that

wget http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm
wget http://rpms.famillecollet.com/enterprise/remi-release-6.rpm
rpm -Uvh remi-release-6*.rpm epel-release-6*.rpm
yum install redis -y

Redis Quick Start

This is a quick start document that targets people without prior experience with Redis. Reading this document will help you:

  • Download and compile Redis to start hacking.
  • Use redis-cli to access the server.
  • Use Redis from your application.
  • Understand how Redis persistence works.
  • Install Redis more properly.
  • Find out what to read next to understand more about Redis.

Installing Redis

The suggested way of installing Redis is compiling it from sources as Redis has no dependencies other than a working GCC compiler and libc. Installing it using the package manager of your Linux distribution is somewhat discouraged as usually the available version is not the latest.

You can either download the latest Redis tar ball from the redis.io web site, or you can alternatively use this special URL that always points to the latest stable Redis version, that is, http://download.redis.io/redis-stable.tar.gz.

In order to compile Redis follow this simple steps:

wget http://download.redis.io/redis-stable.tar.gz
tar xvzf redis-stable.tar.gz
cd redis-stable
make

At this point you can try if your build works correctly typing make test, but this is an optional step. After the compilation the src directory inside the Redis distribution is populated with the different executables that are part of Redis:

  • redis-server is the Redis Server itself.
  • redis-cli is the command line interface utility to talk with Redis.
  • redis-benchmark is used to check Redis performances.
  • redis-check-aof and redis-check-dump are useful in the rare event of corrupted data files.

It is a good idea to copy both the Redis server than the command line interface in proper places using the following commands:

  • sudo cp redis-server /usr/local/bin/
  • sudo cp redis-cli /usr/local/bin/

In the following documentation I assume that /usr/local/bin is in your PATH environment variable so you can execute both the binaries without specifying the full path.

Starting Redis

The simplest way to start the Redis server is just executing the redis-server binary without any argument.

$ redis-server
[28550] 01 Aug 19:29:28 # Warning: no config file specified, using the default config. In order to specify a config file use 'redis-server /path/to/redis.conf'
[28550] 01 Aug 19:29:28 * Server started, Redis version 2.2.12
[28550] 01 Aug 19:29:28 * The server is now ready to accept connections on port 6379
... and so forth ...

In the above example Redis was started without any explicit configuration file, so all the parameters will use the internal default. This is perfectly fine if you are starting Redis just to play a bit with it or for development, but for production environments you should use a configuration file.

To start Redis with a configuration file just give the full path of the configuration file to use as the only Redis argument, for instance: redis-server /etc/redis.conf. You can use the redis.conf file included in the root directory of the Redis source code distribution as a template to write your configuration file.

Check if Redis is working

External programs talk to Redis using a TCP socket and a Redis specific protocol. This protocol is implemented in the Redis client libraries for the different programming languages. However to make hacking with Redis simpler Redis provides a command line utility that can be used to send commands to Redis. This program is called redis-cli.

The first thing to do in order to check if Redis is working properly is sending a PING command using redis-cli:

$ redis-cli ping
PONG

Running redis-cli followed by a command name and its arguments will send this command to the Redis instance running on localhost at port 6379. You can change the host and port used by redis-cli, just try the –help option to check the usage information.

Another interesting way to run redis-cli is without arguments: the program will start into an interactive mode where you can type different commands:

$ redis-cli                                                                
redis 127.0.0.1:6379> ping
PONG
redis 127.0.0.1:6379> set mykey somevalue
OK
redis 127.0.0.1:6379> get mykey
"somevalue"

At this point you can talk with Redis. It is the right time to pause a bit with this tutorial and start the fifteen minutes introduction to Redis data types in order to learn a few Redis commands. Otherwise if you already know a few basic Redis commands you can keep reading.

Using Redis from your application

Of course using Redis just from the command line interface is not enough as the goal is to use it from your application. In order to do so you need to download and install a Redis client library for your programming language. You’ll find a full list of clients for different languages in this page.

For instance if you happen to use the Ruby programming language our best advice is to use the Redis-rb client. You can install it using the command gem install redis (also make sure to install the SystemTimer gem as well).

These instructions are Ruby specific but actually many library clients for popular languages look quite similar: you create a Redis object and execute commands calling methods. A short interactive example using Ruby:

>> require 'rubygems'
=> false
>> require 'redis'
=> true
>> r = Redis.new
=> #<Redis client v2.2.1 connected to redis://127.0.0.1:6379/0 (Redis v2.3.8)>
>> r.ping
=> "PONG"
>> r.set('foo','bar')
=> "OK"
>> r.get('foo')
=> "bar"

Redis persistence

You can learn how Redis persisence works in this page, however what is important to understand for a quick start is that by default, if you start Redis with the default configuration, Redis will spontaneously save the dataset only from time to time (for instance after at least five minutes if you have at least 100 changes in your data), so if you want your database to persist and be reloaded after a restart make sure to call the SAVEcommand manually every time you want to force a data set snapshot. Otherwise make sure to shutdown the database using the SHUTDOWNcommand:

$ redis-cli shutdown

This way Redis will make sure to save the data on disk before quitting. Reading the persistence page is strongly suggested in order to better understand how Redis persistence works.

Installing Redis more properly

Running Redis from the command line is fine just to hack a bit with it or for development. However at some point you’ll have some actual application to run on a real server. For this kind of usage you have two different choices:

  • Run Redis using screen.
  • Install Redis in your Linux box in a proper way using an init script, so that after a restart everything will start again properly.

A proper install using an init script is strongly suggested. The following instructions can be used to perform a proper installation using the init script shipped with Redis 2.4 in a Debian or Ubuntu based distribution.

We assume you already copied redis-server and redis-cli executables under /usr/local/bin.

  • Create a directory where to store your Redis config files and your data: 
    sudo mkdir /etc/redis
sudo mkdir /var/redis
  • Copy the init script that you’ll find in the Redis distribution under the utils directory into /etc/init.d. We suggest calling it with the name of the port where you are running this instance of Redis. For example: 
    sudo cp utils/redis_init_script /etc/init.d/redis_6379
  • Edit the init script. 
    sudo vi /etc/init.d/redis_6379

Make sure to modify REDIS_PORT accordingly to the port you are using. Both the pid file path and the configuration file name depend on the port number.

  • Copy the template configuration file you’ll find in the root directory of the Redis distribution into /etc/redis/ using the port number as name, for instance: 
    sudo cp redis.conf /etc/redis/6379.conf
  • Create a directory inside /var/redis that will work as data and working directory for this Redis instance: 
    sudo mkdir /var/redis/6379
  • Edit the configuration file, making sure to perform the following changes:
    • Set daemonize to yes (by default it is set to no).
    • Set the pidfile to /var/run/redis_6379.pid (modify the port if needed).
    • Change the port accordingly. In our example it is not needed as the default port is already 6379.
    • Set your preferred loglevel.
    • Set the logfile to /var/log/redis_6379.log
    • Set the dir to /var/redis/6379 (very important step!)
  • Finally add the new Redis init script to all the default runlevels using the following command: 
    sudo update-rc.d redis_6379 defaults

You are done! Now you can try running your instance with:

/etc/init.d/redis_6379 start

Make sure that everything is working as expected:

  • Try pinging your instance with redis-cli.
  • Do a test save with redis-cli save and check that the dump file is correctly stored into /var/redis/6379/ (you should find a file called dump.rdb).
  • Check that your Redis instance is correctly logging in the log file.
  • If it’s a new machine where you can try it without problems make sure that after a reboot everything is still working.

Note: in the above instructions we skipped many Redis configurations parameters that you would like to change, for instance in order to use AOF persistence instead of RDB persistence, or to setup replication, and so forth. Make sure to read the redis.conf file (that is heavily commented) and the other documentation you can find in this web site for more information.

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