Clean container registry images in Google Cloud Build step.

cloudbuild.yaml

substitutions:
  _IMG_KEEP: "3"

steps:

  - name: 'gcr.io/cloud-builders/gcloud-slim'
    entrypoint: 'bash'
    args: 
      - '-c'
      - |
        set -e
        
        apt update && apt install -y jq
        
        images="myimage"
        for image in ${images[@]}; do
          echo "Cleaning image ${image}"
          c=0
          image="gcr.io/$PROJECT_ID/${image}"
          number_keep_images=${_IMG_KEEP}

          date=$(gcloud container images list-tags $image --limit=unlimited \
            --sort-by=~TIMESTAMP --format=json | TZ=/usr/share/zoneinfo/UTC jq -r '.['$number_keep_images'].timestamp.datetime | sub("(?<before>.*):"; .before ) | strptime("%Y-%m-%d %H:%M:%S%z") | mktime | strftime("%Y-%m-%d")')

          for digest in $(gcloud container images list-tags $image --limit=unlimited --sort-by=~TIMESTAMP \
            --filter="timestamp.datetime < '${date}'" --format='get(digest)'); do
            (
              set -x
              gcloud container images delete -q --force-delete-tags "${image}@${digest}"
            )
            c=c+1
          done
          echo "Deleted ${c} images for ${image}." >&2
        fi