This has happened to me so many times, I'm writing a blog post just to vent about it.

Today, BLOG FROG's CI failed after I pushed an update. However, it wasn't due to the new code I pushed. To explain what happened, I'll have to give a brief background.

The first step in BLOG FROG's CI is to build its docker image. BLOG FROG's Dockerfile does this in two steps:

  1. Using the Composer 2.4 docker image, install dependencies.
  2. Build BLOG FROG's image from the PHP 8.1 with Apache image, copying dependencies from the previous step.

The CI was failing on the first of these steps: installing dependencies with Composer 2.4. Looking more closely, one of the dependencies was giving this error: 

nette/schema v1.2.2 requires php >=7.1 <8.2 -> your php version (8.2.4) does not satisfy that requirement.

Apparently, at some point, the composer:2.4 image updated to use PHP version 8.2 instead of 8.1, and this was causing a problem with my dependencies. Looking at the Dockerfile for composer:2.4 confirmed that it's built off of php:8-alpine, which must have updated its version in the time between now and the last BLOG FROG update.

This is not the first time I've had CI fail because of a base docker image changing software versions from under my feet. It's one of the gripes I have with docker, or more technically, how docker is used. It's for this reason that I think building your images off of :latest is an antipattern; if you do so, you risk things breaking when the version updates unexpectedly. This is why I try to pin my docker images to specific versions.

However, in this case, pinning to a specific Composer version still introduced the same bug. My error was not pinning to the specific PHP version I needed. I should have realized that the Composer image would be pinned to PHP latest.

To fix the issue, I copied the composer:2.4 Dockerfile contents into my build step and changed the first line so that it builds from php8.1-alpine specifically. This fixed the issue and should hopefully prevent any more unexpected version mismatches moving forward.