Add GitHub Actions to build and push Docker image

.github/workflows/build-and-push-container.yml

@@ -0,0 +1,66 @@
+name: Build and push container to GHCR
+
+# Adapted from .github/workflows/main-ci.yml from
+# https://github.com/metcalfc/docker-action-examples/blob/main/
+# for the OpenDRR Platform
+
+# For all pushes to the master branch, push the image to the
+# GitHub registry under an edge tag so we can use it for the nightly
+# integration tests.
+# For tagged releases, push the image to the GitHub registry
+# an addtional "latest" tag too.
+on:
+  push:
+    branches: master
+    tags:
+      - "v*.*.*"
+      - "*.*.*"
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    steps:
+      # GitHub Actions do not automatically checkout your projects. If you need the code
+      # you need to check it out.
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Prepare
+        id: prep
+        run: |
+          DOCKER_IMAGE=ghcr.io/opendrr/python-env
+          VERSION=edge
+          if [[ $GITHUB_REF == refs/tags/* ]]; then
+            VERSION=${GITHUB_REF#refs/tags/v}
+            VERSION=${VERSION#refs/tags/}
+          fi
+          if [ "${{ github.event_name }}" = "schedule" ]; then
+            VERSION=nightly
+          fi
+          TAGS="${DOCKER_IMAGE}:${VERSION}"
+          if [[ $VERSION =~ ^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3} ]]; then
+            TAGS="$TAGS,${DOCKER_IMAGE}:latest"
+          fi
+          echo ::set-output name=tags::${TAGS}
+
+      - name: Set up Docker Buildx
+        id: buildx
+        uses: docker/setup-buildx-action@v1
+
+      - name: Login to ghcr
+        if: github.event_name != 'pull_request'
+        uses: docker/login-action@v1
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push
+        id: docker_build
+        uses: docker/build-push-action@v2
+        with:
+          builder: ${{ steps.buildx.outputs.name }}
+          context: .
+          push: ${{ github.event_name != 'pull_request' }}
+          tags: ${{ steps.prep.outputs.tags }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max