Docker Buildx vs BuildKit: How They Relate
These are not competitors: BuildKit is the modern Docker build engine, and Buildx is the CLI plugin and driver system that drives BuildKit. You almost always use them together.
A common point of confusion is treating Buildx and BuildKit as alternatives. BuildKit is the backend that actually builds images (concurrent stages, cache mounts, better caching); Buildx is the front-end CLI (docker buildx) that exposes BuildKit features and manages builders. Here is how they relate and what to pick in CI.
| Docker Buildx | BuildKit | |
|---|---|---|
| What it is | CLI plugin + driver manager | The build engine (backend) |
| Role | Drives builds, multi-platform, builders | Executes the build graph |
| Multi-platform | Yes (--platform, emulation/nodes) | Engine support for multi-arch |
| Cache export | Exposes registry/inline/local cache | Implements the cache backends |
| Drivers | docker, docker-container, kubernetes, remote | Runs inside the chosen driver |
| Relationship | Front-end to BuildKit | Back-end used by Buildx |
Engine vs front-end
BuildKit is the engine: it parses the Dockerfile into a DAG, runs independent stages in parallel, and supports advanced features like cache mounts (RUN --mount=type=cache) and secrets. Buildx is the user-facing CLI and driver layer that lets you access those features, build for multiple architectures, and run builds in a dedicated container or Kubernetes builder.
When you need Buildx
For a plain single-arch build, docker build (now backed by BuildKit by default) is enough. Reach for docker buildx when you need multi-platform images, a container/remote builder that persists cache, or explicit cache export/import to a registry. The docker-container driver is what unlocks cross-platform builds and shareable cache.
In CI
On CI, use docker buildx build --cache-to/--cache-from against a registry so each run reuses layers from previous runs, and use the docker-container driver for multi-arch. This turns cold, slow image builds into fast, cache-hit builds.
The verdict
Do not choose between them: BuildKit is the engine and Buildx is the CLI that drives it. Use docker buildx when you need multi-platform builds or exportable cache; otherwise BuildKit already powers your default docker build.