Use Docker buildx cache-to and cache-from backends for faster CI image builds

Steps

1. Create a buildx builder that supports advanced cache backends: docker buildx create --use --name ci-builder --driver docker-container
2. Use the registry cache backend to store layer cache in a dedicated image tag: docker buildx build --cache-to type=registry,ref=YOUR_REGISTRY/myapp:buildcache,mode=max --cache-from type=registry,ref=YOUR_REGISTRY/myapp:buildcache -t YOUR_REGISTRY/myapp:latest --push .
3. For GitHub Actions, use the gha cache backend to store layers in the Actions cache service: add cache-from: type=gha and cache-to: type=gha,mode=max under the build-push-action inputs
4. For multi-stage images, set mode=max to cache all intermediate stages, not just the final stage; mode=min (the default) only caches the final stage and misses most of the speedup
5. When building multi-platform images, export separate per-platform caches because BuildKit cannot merge cache manifests across platforms in a single --cache-to; use a platform-specific tag suffix (e.g., :buildcache-amd64) for each target
6. Verify cache effectiveness by checking build output for CACHED layer markers; a cold build with mode=max populates the cache, and subsequent builds should show most layers as CACHED