feat(ci): skip qemu image build if version already exists in ECR

Add check to prevent rebuilding existing images in ECR repository. The workflow now
verifies if an image with the current version tag exists before proceeding with the
build and publish process.

Author: jfroche

.github/workflows/qemu-image-build.yml

@@ -32,8 +32,33 @@ jobs:
           VERSIONS=$(yq '.postgres_major[1]' ansible/vars.yml | jq -R -s -c 'split("\n")[:-1]')
           echo "postgres_versions=$VERSIONS" >> $GITHUB_OUTPUT
 
-  build:
+  check-existing-image:
     needs: prepare
+    runs-on: ubuntu-latest
+    outputs:
+      image_exists: ${{ steps.check-image.outputs.image_exists }}
+    steps:
+      - name: Checkout Repo
+        uses: supabase/postgres/.github/actions/shared-checkout@HEAD
+
+      - name: Check if image already exists in ECR
+        id: check-image
+        env:
+          AWS_REGION: us-east-1
+          REPOSITORY: postgres-vm-image
+        run: |
+          VERSION=$(yq '.postgres_release["postgres'${{ fromJson(needs.prepare.outputs.postgres_versions) }}'"]' ansible/vars.yml | tr -d '"')
+          if aws ecr describe-images --repository-name $REPOSITORY --image-ids imageTag=$VERSION --region $AWS_REGION 2>/dev/null; then
+            echo "::notice title=Qemu image::Image with tag $VERSION already exists. Skipping build. Please update the version in ansible/vars.yml if you want to upload a new image."
+            echo "image_exists=true" >> $GITHUB_OUTPUT
+          else
+            echo "Image with tag $VERSION does not exist. Proceeding with build."
+            echo "image_exists=false" >> $GITHUB_OUTPUT
+          fi
+
+  build:
+    needs: [prepare, check-existing-image]
+    if: ${{ needs.check-existing-image.outputs.image_exists == 'false' }}
     strategy:
       matrix:
         postgres_version: ${{ fromJson(needs.prepare.outputs.postgres_versions) }}