Docker image size matters. Here’s how you build a small image on top of debian:slim and why that’s a better option than alpine or scratch.

The topic of this post is neither new nor original, so I’m going to keep things short. People have been using jemalloc with MRI Ruby for years and praising it’s benefits all the while. The TL;DR here is: for Rails apps, using jemalloc will reduce memory consumption and might increase performance a little.

Why?

To illustrate my own experience, here’s a Grafana graph showing the effect of switching to jemalloc on a production server running a few instances of a Rails application: