Quick Docker commands to troubleshoot networking in GitHub Actions runners—inject host.docker.internal and test reachability, including auto-detecting private IP.

ci.yml

  check-env:
    permissions:
      contents: read
      pull-requests: write
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - name: Set up Ruby
        uses: ruby/setup-ruby@v1
        with:
          ruby-version: .ruby-version
          bundler-cache: true
      - name: Check env
        run: |
          env
          docker info
          docker run --rm --add-host "host.docker.internal:host-gateway"  alpine:latest cat /etc/hosts 
          docker run --rm --add-host "host.docker.internal:host-gateway"  alpine:latest ping -c 1 host.docker.internal
          docker run --rm --add-host "host.docker.internal:host-gateway"  alpine:latest ping -c 1 $(ruby -rsocket -e 'puts Socket.ip_address_list.detect(&:ipv4_private?).ip_address')