Bootc Matrix Build

Running a Fedora-based bootc image stack means tracking multiple Fedora releases in parallel. Instead of duplicating every job in the workflow, I wired up the matrix strategy in Forgejo Actions to build F43 and F44 from a single job definition.

The Problem With Hardcoded Versions

Before, every Containerfile had a hardcoded base image:

FROM git.m1ch.eu/oci/c-os:base-43

Supporting F44 would have meant either duplicating the whole workflow or a manual find-and-replace for every release. Neither scales.

Parametrize the Containerfile

First, replace the hardcoded tag with a build arg:

ARG FEDORA_VERSION=43
FROM git.m1ch.eu/oci/c-os:docker-${FEDORA_VERSION}

The default stays 43 so local builds without –build-arg still work.

Add the Matrix

Each job in the orchestrating workflow gets a strategy.matrix block:

jobs:
  build_docker_site_a:
    strategy:
      matrix:
        fedora_version: ["43", "44"]
    uses: ./.forgejo/workflows/build_and_push.yaml
    with:
      tag: docker_site_a
      dir: docker
      fedora_version: ${{ matrix.fedora_version }}
      latest_version: ${{ inputs.latest_version || '43' }}

Forgejo spawns one job instance per matrix value. Each produces a distinct tag: docker_site_a-43 and docker_site_a-44.

The latest_version input controls which Fedora version gets the unversioned convenience tag (e.g. docker_site_a). It defaults to 43 and can be overridden at dispatch time when promoting F44 to stable.

The Reusable Workflow

The reusable workflow receives fedora_version as an input and threads it through to podman build:

inputs:
  fedora_version:
    required: false
    default: "43"
    type: string
  latest_version:
    required: false
    default: "43"
    type: string

  ...
  
    podman build \
      --build-arg FEDORA_VERSION=${{ inputs.fedora_version }} \
      -t ${REGISTRY}/${REPO}:${TAG}-${{ inputs.fedora_version }} \
      ${{ inputs.dir }}

Adding a New Fedora Version

When F45 ships, the change is one line in each build.yaml:

fedora_version: ["43", "44", "45"]

No Containerfile edits needed.