Use the docker/metadata-action Action to generate metadata

Switch to using the docker/metadata-action GitHub Action to generate Docker image metadata. This replaces manually specifying the labels and calculating appropriate tags. This approach will both be easier as well as eliminate some of the issues we've had with manually calculating the image tags.
cisagov · Jan 10, 2025 · 1518b9a · 1518b9a
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commit 1518b9a
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diff --git a/.github/dependabot.yml b/.github/dependabot.yml
@@ -29,10 +29,10 @@ updates:
       - dependency-name: step-security/harden-runner
       # Managed by cisagov/skeleton-docker
       # - dependency-name: actions/download-artifact
-      # - dependency-name: actions/github-script
       # - dependency-name: actions/upload-artifact
       # - dependency-name: docker/build-push-action
       # - dependency-name: docker/login-action
+      # - dependency-name: docker/metadata-action
       # - dependency-name: docker/setup-buildx-action
       # - dependency-name: docker/setup-qemu-action
       # - dependency-name: github/codeql-action

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
@@ -193,54 +193,13 @@ jobs:
         uses: mxschmitt/action-tmate@v3
         if: env.RUN_TMATE
   prepare:
-    # Calculates and publishes outputs that are used by other jobs.
-    #
-    # Outputs:
-    #   created:
-    #     The current date-time in RFC3339 format.
-    #   repometa:
-    #     The json metadata describing this repository.
-    #   source_version:
-    #     The source version as reported by the `bump-version show` command.
-    #   tags:
-    #     A comma separated list of Docker tags to be applied to the images on
-    #     Docker Hub.  The tags will vary depending on:
-    #     - The event that triggered the build.
-    #     - The branch the build is based upon.
-    #     - The git tag the build is based upon.
-    #
-    #     When a build is based on a git tag of the form `v*.*.*` the image will
-    #     be tagged on Docker Hub with multiple levels of version specificity.
-    #     For example, a git tag of `v1.2.3+a` will generate Docker tags of
-    #     `:1.2.3_a`, `:1.2.3`, `:1.2`, `:1`, and `:latest`.
-    #
-    #     Builds targeting the default branch will be tagged with `:edge`.
-    #
-    #     Builds from other branches will be tagged with the branch name. Solidi
-    #     (`/` characters - commonly known as slashes) in branch names are
-    #     replaced with hyphen-minuses (`-` characters) in the Docker tag.  For
-    #     more information about the solidus see these links:
-    #       * https://www.compart.com/en/unicode/U+002F
-    #       * https://en.wikipedia.org/wiki/Slash_(punctuation)#Encoding
-    #
-    #     Builds triggered by a push event are tagged with a short hash in the
-    #     form: sha-12345678
-    #
-    #     Builds triggered by a pull request are tagged with the pull request
-    #     number in the form pr-123.
-    #
-    #     Builds triggered using the GitHub GUI (workflow_dispatch) are tagged
-    #     with the value specified by the user.
-    #
-    #     Scheduled builds are tagged with `:nightly`.
+    # Generate Docker image metadata using the docker/metadata-action GitHub Action.
     name: Prepare build variables
     needs:
       - diagnostics
     outputs:
-      created: ${{ steps.prep.outputs.created }}
-      repometa: ${{ steps.repo.outputs.result }}
-      source_version: ${{ steps.prep.outputs.source_version }}
-      tags: ${{ steps.prep.outputs.tags }}
+      labels: ${{ steps.generate-metadata.outputs.labels }}
+      tags: ${{ steps.generate-metadata.outputs.tags }}
     permissions:
       # actions/checkout needs this to fetch code
       contents: read
@@ -256,53 +215,23 @@ jobs:
         with:
           egress-policy: audit
       - uses: actions/checkout@v4
-      - name: Gather repository metadata
-        id: repo
-        uses: actions/github-script@v7
+      - id: generate-metadata
+        name: Generate Docker image metadata
+        uses: docker/metadata-action@v5
         with:
-          script: |
-            const repo = await github.rest.repos.get(context.repo)
-            return repo.data
-      - name: Calculate output values
-        id: prep
-        run: |
-          VERSION=noop
-          SEMVER="^v(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)(-((0|[1-9][0-9]*|[0-9]*[a-zA-Z-][0-9a-zA-Z-]*)(\.(0|[1-9][0-9]*|[0-9]*[a-zA-Z-][0-9a-zA-Z-]*))*))?(\+([0-9a-zA-Z-]+(\.[0-9a-zA-Z-]+)*))?$"
-          if [ "${{ github.event_name }}" = "schedule" ]; then
-            VERSION=nightly
-          elif [ "${{ github.event_name }}" = "workflow_dispatch" ]; then
-            VERSION=${{ github.event.inputs.image-tag }}
-          elif [[ $GITHUB_REF == refs/tags/* ]]; then
-            VERSION=${GITHUB_REF#refs/tags/}
-          elif [[ $GITHUB_REF == refs/heads/* ]]; then
-            VERSION=$(echo ${GITHUB_REF#refs/heads/} | sed -r 's#/+#-#g')
-            if [ "${{ github.event.repository.default_branch }}" = "$VERSION" ];
-              then
-              VERSION=edge
-            fi
-          elif [[ $GITHUB_REF == refs/pull/* ]]; then
-            VERSION=pr-${{ github.event.number }}
-          fi
-          if [[ $VERSION =~ $SEMVER ]]; then
-            VERSION_NO_V=${VERSION#v}
-            MAJOR="${BASH_REMATCH[1]}"
-            MINOR="${BASH_REMATCH[2]}"
-            PATCH="${BASH_REMATCH[3]}"
-            TAGS="${IMAGE_NAME}:${VERSION_NO_V//+/_},${IMAGE_NAME}:${MAJOR}.${MINOR}.${PATCH},${IMAGE_NAME}:${MAJOR}.${MINOR},${IMAGE_NAME}:${MAJOR},${IMAGE_NAME}:latest"
-          else
-            TAGS="${IMAGE_NAME}:${VERSION}"
-          fi
-          if [ "${{ github.event_name }}" = "push" ]; then
-            TAGS="${TAGS},${IMAGE_NAME}:sha-${GITHUB_SHA::8}"
-          fi
-          for i in ${TAGS//,/ }
-          do
-            TAGS="${TAGS},ghcr.io/${i}"
-          done
-          echo "created=$(date -u +'%Y-%m-%dT%H:%M:%SZ')" >> $GITHUB_OUTPUT
-          echo "source_version=$(./bump-version show)" >> $GITHUB_OUTPUT
-          echo "tags=${TAGS}" >> $GITHUB_OUTPUT
-          echo tags=${TAGS}
+          images: |
+            ${{ env.IMAGE_NAME }}
+            ghcr.io/${{ env.IMAGE_NAME }}
+          tags: |
+            type=edge,branch=develop
+            type=ref,event=branch
+            type=ref,event=pr
+            type=ref,event=tag
+            type=schedule
+            type=semver,pattern={{major}}
+            type=semver,pattern={{major}}.{{minor}}
+            type=semver,pattern={{version}}
+            type=sha
       - name: Setup tmate debug session
         uses: mxschmitt/action-tmate@v3
         if: github.event.inputs.remote-shell == 'true' || env.RUN_TMATE
@@ -352,29 +281,7 @@ jobs:
           cache-to: type=local,dest=${{ env.BUILDX_CACHE_DIR }}
           context: .
           file: ./Dockerfile
-          labels: "\
-            org.opencontainers.image.created=${{
-              needs.prepare.outputs.created }}
-
-            org.opencontainers.image.description=${{
-              fromJson(needs.prepare.outputs.repometa).description }}
-
-            org.opencontainers.image.licenses=${{
-              fromJson(needs.prepare.outputs.repometa).license.spdx_id }}
-
-            org.opencontainers.image.revision=${{ github.sha }}
-
-            org.opencontainers.image.source=${{
-              fromJson(needs.prepare.outputs.repometa).clone_url }}
-
-            org.opencontainers.image.title=${{
-              fromJson(needs.prepare.outputs.repometa).name }}
-
-            org.opencontainers.image.url=${{
-              fromJson(needs.prepare.outputs.repometa).html_url }}
-
-            org.opencontainers.image.version=${{
-              needs.prepare.outputs.source_version }}"
+          labels: ${{ steps.generate-metadata.outputs.labels }}
           outputs: type=docker,dest=dist/image.tar
           # Uncomment the following option if you are building an image for use
           # on Google Cloud Run or AWS Lambda. The current default image output
@@ -518,29 +425,7 @@ jobs:
           cache-to: type=local,dest=${{ env.BUILDX_CACHE_DIR }}
           context: .
           file: ./Dockerfile-x
-          labels: "\
-            org.opencontainers.image.created=${{
-              needs.prepare.outputs.created }}
-
-            org.opencontainers.image.description=${{
-              fromJson(needs.prepare.outputs.repometa).description }}
-
-            org.opencontainers.image.licenses=${{
-              fromJson(needs.prepare.outputs.repometa).license.spdx_id }}
-
-            org.opencontainers.image.revision=${{ github.sha }}
-
-            org.opencontainers.image.source=${{
-              fromJson(needs.prepare.outputs.repometa).clone_url }}
-
-            org.opencontainers.image.title=${{
-              fromJson(needs.prepare.outputs.repometa).name }}
-
-            org.opencontainers.image.url=${{
-              fromJson(needs.prepare.outputs.repometa).html_url }}
-
-            org.opencontainers.image.version=${{
-              needs.prepare.outputs.source_version }}"
+          labels: ${{ needs.prepare.outputs.labels }}
           platforms: ${{ env.PLATFORMS }}
           # Uncomment the following option if you are building an image for use
           # on Google Cloud Run or AWS Lambda. The current default image output