A poor man's Nix CI cache

Wed, 21 Oct 2026 11:20:00 +0200

A thing I often come back to is speeding up CI. For almost 20 years I’ve been pushing compilation-heavy code to GitHub. Their free tier always provided enough CI minutes. So optimizing was never a resource problem, but rather a principle.

For GitHub Actions, my go-to strategy is nixbuild/nix-quick-install-action and nix-community/cache-nix-action that piggyback on the GitHub CI cache:

jobs:
 build:
 runs-on: ubuntu-latest

 steps:
 - name: Checkout
 uses: actions/checkout@d23441a48e516b6c34aea4fa41551a30e30af803 # v6.1.0, 2026-07-16

 - uses: nixbuild/nix-quick-install-action@9f63be77f412a248c9d9a65a4c82cf066cdf8f0c # v35, 2026-06-17

 - name: Restore and save Nix store
 uses: nix-community/cache-nix-action@7df957e333c1e5da7721f60227dbba6d06080569 # v7.0.2, 2026-01-30
 with:
 primary-key: nix-${{ runner.os }}-${{ hashFiles('**/*.nix', '**/flake.lock') }}
 restore-prefixes-first-match: nix-${{ runner.os }}-
 gc-max-store-size-linux: 2G
 purge: true
 purge-prefixes: nix-${{ runner.os }}-
 purge-created: 0
 purge-last-accessed: P1DT12H
 purge-primary-key: never

However, I also run a Forgejo instance with a NixOS-like CI runner that cannot benefit from these community actions.

Forgejo on Simon Shine

A poor man's Nix CI cache