CI: Add image caching to when we update the CI image.

.github/workflows/build-ais-ci-image.yml

@@ -24,10 +24,6 @@ jobs:
     container: docker:28.5
     outputs:
       new_ci_image: ${{ steps.ci-image.outputs.AIS_CI_IMAGE }}
-      image_tag: ${{ steps.ci-image.outputs.AIS_CI_IMAGE_TAG }}
-      # image_tag is a bit hacky. GitHub does not support separating outputs
-      # from a workflow run in a matrix. The last workflow to run will set the
-      # output value. `image_tag` is constant across matrix jobs so this is fine.
     steps:
       - name: Set CI environment variables
         run: |
@@ -38,6 +34,8 @@ jobs:
         run: |
           echo "AIS_CI_IMAGE=${{ env.AIS_DOCKER_REGISTRY }}/${{ env.AIS_CI_IMAGE_NAME}}:${AIS_CI_IMAGE_TAG}" \
             >> "${GITHUB_OUTPUT}"
+          echo "AIS_CI_LATEST_CACHE=${{ env.AIS_DOCKER_REGISTRY }}/${{ env.AIS_CI_IMAGE_NAME}}:latest-cache" \
+            >> "${GITHUB_OUTPUT}"
       - name: Fetching code repository...
         uses: actions/checkout@v5
       - name: Authenticating to GitHub Container Registry.
@@ -62,6 +60,7 @@ jobs:
               PR URL: ${{ env.AIS_PR_BASE_URL }}/${AIS_PR_NUMBER}" \
             --build-arg BUILDKIT_INLINE_CACHE=1 \
             --cache-from=type=registry,ref=${{ steps.ci-image.outputs.AIS_CI_IMAGE }} \
+            --cache-from=type=registry,ref=${{ steps.ci-image.outcome.AIS_CI_LATEST_CACHE }} \
             --push \
             -t ${{ steps.ci-image.outputs.AIS_CI_IMAGE }} \
             ${GITHUB_WORKSPACE}

.github/workflows/update-ais-ci-image.yml

@@ -8,6 +8,12 @@ on:
       - develop
   workflow_dispatch:
     # Requires write access to trigger.
+    inputs:
+      pull_from_cache:
+        description: Build image with 'latest' cache
+        required: false
+        default: true
+        type: boolean
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
@@ -19,7 +25,7 @@ jobs:
     env:
       AIS_DOCKER_REGISTRY: ghcr.io/rocm/hipfile
       AIS_CI_IMAGE_NAME: ais_ci_${{ matrix.supported_platforms }}
-    if: ${{ github.event.pull_request.merged == true }}
+    if: ${{ github.event.pull_request.merged == true || github.event_name == 'workflow_dispatch' }}
     runs-on: [ubuntu-24.04]
     container: docker:28.5
     strategy:
@@ -42,20 +48,33 @@ jobs:
         run: |
           echo "AIS_CI_IMAGE=${{ env.AIS_DOCKER_REGISTRY }}/${{ env.AIS_CI_IMAGE_NAME}}:latest" \
             >> "${GITHUB_OUTPUT}"
+      - name: Set Docker Cache Instruction
+        id: use-cache
+        # If triggered by a pull_request, pull_from_cache will be null. Note
+        # however `false == null` resolves to `true`. Use empty string to check
+        # for 'null'.
+        # See: https://docs.github.com/en/actions/reference/workflows-and-actions/expressions
+        # for how null gets converted when compared to non-null, and converted into a string.
+        run: >-
+          echo "CACHE_FROM_CMD=${{
+            ( format('{0}', inputs.pull_from_cache) == '' || inputs.pull_from_cache ) &&
+            format('--cache-from=type=registry,ref=\"{0}-cache\"', steps.ci-image.outputs.AIS_CI_IMAGE) ||
+            ''
+          }}" >> "${GITHUB_OUTPUT}"
       - name: Setup Docker Builder
         uses: docker/setup-buildx-action@v3.11.1
         with:
           name: ais-builder
           driver: docker-container
           cache-binary: false # True uses the GHA Cache Backend.
-      # We won't use the cache from the previous image.
-      # This lets us semi-regularly pull in package updates automatically.
       - name: Build & Push latest image for AIS CI
         run: |
           docker buildx build \
             -f ${GITHUB_WORKSPACE}/util/docker/DOCKERFILE.${{ env.AIS_CI_IMAGE_NAME }} \
             --label "org.opencontainers.image.description= \
               Latest AIS CI Image for ${{ matrix.supported_platforms }}." \
+            --cache-to=type=registry,ref="${{ steps.ci-image.outputs.AIS_CI_IMAGE }}-cache" \
+            ${{ steps.use-cache.outputs.CACHE_FROM_CMD }} \
             --push \
             -t ${{ steps.ci-image.outputs.AIS_CI_IMAGE }} \
             ${GITHUB_WORKSPACE}