runner.yml

name: Build & Publish External Runner Image

on:
  push:
    branches: [master]
    paths:
      - 'runner/**'
      - 'forge/**'
      - '.github/workflows/runner.yml'
  workflow_dispatch:
    inputs:
      tag:
        description: 'Image tag (e.g. v1.0.0)'
        required: false
        default: ''

permissions:
  contents: read
  packages: write
  id-token: write   # required for Sigstore keyless signing

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v3

      - name: Install cosign
        uses: sigstore/cosign-installer@v3

      - name: Log in to GHCR
        uses: docker/login-action@v3
        with:
          registry: ghcr.io
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - name: Derive tags
        id: tags
        run: |
          SHA="${GITHUB_SHA::12}"
          INPUT_TAG="${{ github.event.inputs.tag }}"
          IMAGE="ghcr.io/forge-nc/forge-external-runner"
          TAGS="${IMAGE}:${SHA}"
          if [ "${GITHUB_REF}" = "refs/heads/master" ]; then
            TAGS="${TAGS},${IMAGE}:latest,${IMAGE}:v1"
          fi
          if [ -n "$INPUT_TAG" ]; then
            TAGS="${TAGS},${IMAGE}:${INPUT_TAG}"
          fi
          echo "tags=${TAGS}" >> "$GITHUB_OUTPUT"
          echo "image=${IMAGE}" >> "$GITHUB_OUTPUT"

      - name: Build and push
        id: push
        uses: docker/build-push-action@v6
        with:
          context: .
          file: runner/Dockerfile.runner
          push: true
          tags: ${{ steps.tags.outputs.tags }}
          cache-from: type=gha
          cache-to: type=gha,mode=max

      - name: Sign image with Sigstore (keyless, OIDC)
        env:
          COSIGN_EXPERIMENTAL: 1
          DIGEST: ${{ steps.push.outputs.digest }}
          IMAGE: ${{ steps.tags.outputs.image }}
        run: |
          cosign sign --yes "${IMAGE}@${DIGEST}"

      - name: Emit digest for .well-known update
        run: |
          echo "Image digest: ${{ steps.push.outputs.digest }}"
          echo "Update /.well-known/forge-origin.json runner_image_digest field to this value."