Docker builder machine specifications

The usual Docker-in-CI pattern exports the layer cache to a registry or to the Actions cache at the end of every job and imports it at the start of the next. For a large image that export/import round-trip can cost more than the build it was supposed to save.

A remote builder keeps the cache where BuildKit already wants it — on the builder's own disk. Your job attaches to a warm instance, builds, and detaches. Nothing is exported.

jobs:
  image:
    runs-on: runnerhut-4vcpu-ubuntu-2404
    steps:
      - uses: actions/checkout@v4
      - uses: runnerhut/setup-buildx@v1
      - uses: docker/build-push-action@v6
        with:
          push: true
          tags: ghcr.io/acme/api:${{ github.sha }}