How to Enforce a Docker Image Size Budget in GitHub Actions

Reading the built image size with docker inspect and comparing it to a budget stops an image from silently bloating.

Build the image, read its size from docker image inspect -f "{{.Size}}", and exit non-zero when it exceeds the budget. The dive tool can break down wasted layers.

Steps

• Build the image with a tag.
• Read the size with docker image inspect -f "{{.Size}}".
• Compare the byte value to a budget and fail when over.

Workflow

jobs:
  image-size:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - run: docker build -t myapp:ci .
      - name: Enforce image size budget
        run: |
          BYTES=$(docker image inspect -f '{{.Size}}' myapp:ci)
          BUDGET=$((250 * 1024 * 1024))
          echo "image=$((BYTES/1024/1024))MB budget=250MB"
          test "$BYTES" -le "$BUDGET"

Gotchas

• .Size is the uncompressed image size, larger than the compressed registry size.
• A multi-stage build and a slim base image are the usual fixes for an over-budget image.

Related guides