Redis Installation and Configuration

Redis installation and configuration

Redis keeps data in memory and serves it an order of magnitude faster than disk. It is used as a site cache, session storage and a job queue.

What is included

• installing and configuring the service;
• a memory limit and an eviction policy — without them Redis consumes all free memory and the system starts killing processes;
• access protection: binding to the local interface, a password;
• the PHP extension for working with Redis;
• connecting the site: cache, sessions, or both;
• separate key namespaces where several sites share a server;
• cache hit rate verification — if it is low, the setup achieves nothing.

Two typical mistakes

Redis reachable from outside without a password. The classic: the service listens on all interfaces and anyone can read or wipe the data. For session storage that means someone can hijack a user's session.

A shared key namespace across sites. Two stores on one server overwrite each other's cache, and their owners see odd things: someone else's prices, someone else's category names.

When Redis is not needed

On a site with modest traffic and a small catalogue you will not notice a difference — the file cache copes. Redis pays off where there is load.