17 October, 2016

Multiple instances of redis

In the last post I have covered how to install redis server on Centos/Rhel using rpm method and yum method and some troubleshooting skills.

In this post i am going to cover how to install and configure redis to run with multiple ports.

But why we need more ports ?

If you have read my earlier post , you already know that by default redis runs on single port 6379, which any one can use it for small website to cache the data. But for heavy website like magento we need to use additional ports along with 6379 to serve different cache from different ports.

Like in Magento there is simple cache which is normally stored under /var/cache directory. Then there is Full Page Cache which is stored under /var/full_page_cache and session cache which is stored under /var/session_cache.

Note : Discussion about cache/full page cache/session is not under the scope for this document.

Where it is Beneficial then ?

Many of the website are using redis to fasten their response time to the end user using the advantages of redis. So if you want your website should serve as fast as possible then you should think of using redis in your environment.

But for beginners the question is ? how redis does that ? so the simplest answer i can give is 
when you visit any website for first time, your browser sends a request to the server asking for data
the server in return get the data from the application/database hosted on server and serve to browser and then to you.

This is the normal situation, where there is only browser-server in back-end application (may be php) and database (may be mysql)

but when redis is in use, browser sends the request to the server, it then checks whether the request which browser has made is available in redis database or not (means cache here), if the data present then it get served to the browser from redis itself, so here asking data from application/database gets eliminated.

so the total computation power needed for any application/database to generate requested data for the browser get saved. and then get served by REDIS. This situation is very much needed in environment   serving lots of users like some big social media sites and eCommerce sites.

Create Multiple Instances of Redis 

So, let move towards creating additional instances of redis, I am assuming you already have installed redis on your linux server, if in any case if you are not, then you refer the LINK for the installation of redis on Centos/Rhel server.

    Step 1 :  Check first redis is listening on its default port i.e 6379 by running below command.

    which means your redis single instance is UP and running on the server. Now after every package installation normally two types of files gets created for redis.
    • First is init file
    • Second is Configuration file
    Init file location on the Centos/Rhel server is /etc/init.d/
    Configuration file location on Centos/Rhel server is /etc/redis.conf

    Step 2 
    : Now, install it using below command.

    Which means your redis package is installed now on your linux machine using rpm method.

    By YUM Method :-

    Step 1 :  For yum method, we first need to install repository containing the redis package by running below command

    it will create "epel.repo" file under /etc/yum.repos.d/

    That its redis is installed on your server now using yum method. Only difference between rpm method and yum method is yum finds the dependecny of package required for redis to get it install.

    means if redis also need to redis-server package to run properly then yum will install both at the same time.But rpm will not do it, instead it will install only redis package on the server.
    Status Check

    Next thing is to check how to verify redis is working properly or not, so to check that we have to run below commands

    commands explains it all, but thats command will run only on Centos/RHEL server upto OS version 6. For RHEL/Centos 7 there will be different commands to run.


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