Scaling Memcached and Redis for Open edX

Summary

If you’re looking for a general overview of how to scale the Open edX platform then you should read this first, “Scaling Open edX“. You might also want to take a look at the automated tools included in Cookiecutter Open edX Devops as well as this article on Managing Your Open edX Backend With Terraform.

The Open edX platform persists data across five distinct subsystems: MySQL, MongoDB, the Ubuntu file system, Memcached, and since the Lilac release in May 2021, Redis. To scale the Open edX platform you first must physically separate the executable program code from the data that is managed by these four subsystems. This article explains how to migrate the Memcached service. By scaling, I mean migrating Open edX’s local Memcached service to its own independent Ubuntu EC2 instance.

This article describes my preferred approach, which is to use AWS EC2 console to create a new Ubuntu EC2 instance using the same version of Ubuntu on which your Open edX platform currently runs. As of this writing Open edX Lilac runs on Ubuntu 20.04 LTS. I install the latest versions of memcached and redis-server, regardless of the versions that the original Open edX server is using. When scaling Memcached and Redis I do not migrate data.

Note that you will only need to focus on vertical scaling for Memcached and Redis on Open edX. You can safely start with a t2.small or t2.medium EC2 instance size which will probably server your needs for the lifetime of your Open edX platform.