Docker and Container WorkflowsLesson 3.4

How to use Docker layer caching in GitHub Actions

BuildKit cache, cache-from, cache-to, gha cache type, registry cache, layer cache hit, cache invalidation, build speed optimization

Why Docker Builds Are Slow

Docker builds images layer by layer. If a layer's inputs change, that layer and all layers below it must be rebuilt. Without caching, every CI run rebuilds all layers including slow steps like apt-get install.

GitHub Actions Cache Backend

- uses: docker/build-push-action@v5
  with:
    context: .
    push: true
    tags: ghcr.io/${{ github.repository }}:latest
    cache-from: type=gha
    cache-to: type=gha,mode=max

type=gha uses the GitHub Actions cache backend (the same one as actions/cache) to store Docker layer data. cache-from reads from the cache. cache-to writes to it after a successful build. mode=max caches all layers including intermediate ones — mode=min only caches the final image layers.

Registry Cache (Alternative)

For private repositories with large images, using a registry as the cache backend is more efficient:

cache-from: type=registry,ref=ghcr.io/${{ github.repository }}:cache
cache-to: type=registry,ref=ghcr.io/${{ github.repository }}:cache,mode=max

This stores cache data as a manifest in your container registry, surviving beyond GitHub's 7-day cache eviction window.