What is Docker BuildKit and why is it better?

BuildKit is the next-generation build backend for Docker, enabled by default in Docker Desktop and Docker Engine 23.0+. It provides significant improvements over the legacy builder: (1) Parallel building: BuildKit analyzes stage dependencies and builds independent stages in parallel; (2) Better cache: cache is more granular and can be exported/imported across machines (inline cache in registry, external cache with --cache-from/--cache-to); (3) Secrets at build time: RUN --mount=type=secret,id=npmrc cat /run/secrets/npmrc — pass secrets without baking them into image layers; (4) SSH forwarding: RUN --mount=type=ssh git clone git@github.com:private/repo — use SSH keys without embedding them; (5) Bind mounts in RUN: RUN --mount=type=bind,source=.,target=/src; (6) Cache mounts: RUN --mount=type=cache,target=/root/.npm npm install — persistent cache between builds (huge for npm, pip, apt); (7) Faster and more informative output; (8) Multi-platform builds with docker buildx. Enable in older versions: DOCKER_BUILDKIT=1 docker build .. Use docker buildx build for full BuildKit features. BuildKit is the foundation for multi-architecture image building.