Github Actions: added PR builder and release hub push (#67)

* Github Actions: added PR builder and release hub push

* README: updated release management docs

* Main: enable variant-less build and latest

Co-authored-by: Bryan Latten <latten@adobe.com>

.github/workflows/main.yml

@@ -0,0 +1,75 @@
+name: main
+
+on:
+  push:
+    tags:
+    - '*'
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    env:
+      IMAGE_BASE: behance/docker-base
+    strategy:
+      matrix:
+        props:
+        # This is the default variant-less distribution (ex. 3.2.1)
+        - Dockerfile: Dockerfile-ubuntu-20.04
+        # Variant distributions below all have semantic versions + suffix (ex. 3.2.1-ubuntu-18.04)
+        - Dockerfile: Dockerfile-ubuntu-18.04
+          suffix: ubuntu-18.04
+        - Dockerfile: Dockerfile-ubuntu-20.04
+          suffix: ubuntu-20.04
+        - Dockerfile: Dockerfile-alpine
+          suffix: alpine
+        - Dockerfile: Dockerfile-centos-7
+          suffix: centos-7
+        - Dockerfile: Dockerfile-centos-8
+          suffix: centos-8
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v2
+      -
+        name: Add tag suffix
+        if: matrix.props.suffix
+        run: |
+          echo TAG_SUFFIX="-${{ matrix.props.suffix }}" >> $GITHUB_ENV
+      -
+        name: Docker meta
+        id: meta
+        if: github.event_name != 'pull_request'
+        uses: docker/metadata-action@v3
+        with:
+          images: ${{ env.IMAGE_BASE }}
+          tags: |
+            type=semver,pattern={{major}}.{{minor}}.{{patch}}
+            type=semver,pattern={{major}}.{{minor}}
+            type=semver,pattern={{major}}
+          flavor: |
+            latest=auto
+            suffix=${{ env.TAG_SUFFIX }}
+      -
+        name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+      -
+        name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      -
+        name: Login to DockerHub
+        if: github.event_name != 'pull_request'
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      -
+        name: Build + push
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          platforms: linux/amd64,linux/arm64
+          file: ${{ matrix.props.Dockerfile }}
+          tags: ${{ steps.meta.outputs.tags }}
+          push: ${{ github.event_name != 'pull_request' }}

README.md

@@ -132,3 +132,15 @@ Directory | Use
 `/etc/services-available/` | same as above, but must be symlinked into `/etc/services.d/` to take effect
 `/run.d/` | shell scripts (ending in .sh) that make runtime modifications ahead of S6 initialization
 `/scripts` | convenience scripts that can be leveraged in derived images
+
+### Release Management
+
+Github actions provide the machinery for producing tags distributed through Docker Hub. Once a tested and approved PR is merged, simply cutting a new semantically-versioned tag will generate the following matrix of tagged builds:
+- `[major].[minor].[patch](?-variant)`
+- `[major].[minor](?-variant)`
+- `[major](?-variant)`
+Platform support is available for architectures:
+- `linux/arm64`
+- `linux/amd64`
+
+To add new variant based on a new Dockerfile, add an entry to the `matrix.props` with its file and variant suffix.