[azlekov]

What

Two opt-in knobs. With neither set, docker compose config renders the same services, labels and volumes as today.

• RUNNER_<N>_LABELS (runner, runner-2, runner-3) replaces LABELS for that one runner. A host whose runners are all light can let one of them also take large builds, without a second host file.
  • The runner environment moves to its own anchor (x-runner-env). A <<: merge replaces a whole mapping, so a service could not otherwise change LABELS without dropping every other variable.
• COMPOSE_PROFILES=control adds control and control-2:
  • Ephemeral like the others.
  • Labelled only CONTROL_LABELS (default control), so no build or test can land on them.
  • No docker.sock, no tool cache: only a work volume and the read-only action cache.
  • Meant for the short jobs a merge waits on (a picker, a required summary job), so those never queue behind long builds.

Checked

docker compose config with a test .env:

• Default: 3 runners plus the pruner, every runner on the host LABELS, unchanged.
• RUNNER_3_LABELS=…,large: only runner-3 changes.
• COMPOSE_PROFILES=control: two control runners. Each has the full App environment, EPHEMERAL=true, LABELS=control, the <prefix>-control name, only runner-work-control* and the action cache, and the same healthcheck.
• COMPOSE_FILE=docker-compose.yml:hosts/no-caches.compose.yml: still valid.

The nested default ${RUNNER_3_LABELS:-${LABELS:-docker}} was verified with Compose v5.1.2. Hosts need a Compose version with nested interpolation (2.x and later).

🤖 Generated with Claude Code