Dockerfile Frontend in BuildKit

--- title: Custom Dockerfile syntax description: Dive deep into the Dockerfile frontend, and learn about custom frontends keywords: build, buildkit, dockerfile, frontend aliases: - /build/buildkit/dockerfile-frontend/ - /build/dockerfile/frontend/ --- ## Dockerfile frontend BuildKit supports loading frontends dynamically from container images. To use an external Dockerfile frontend, the first line of your [Dockerfile](/reference/dockerfile.md) needs to set the [`syntax` directive](/reference/dockerfile.md#syntax) pointing to the specific image you want to use: ```dockerfile # syntax=[remote image reference] ``` For example: ```dockerfile # syntax=docker/dockerfile:1 # syntax=docker.io/docker/dockerfile:1 # syntax=example.com/user/repo:tag@sha256:abcdef... ``` You can also use the predefined `BUILDKIT_SYNTAX` build argument to set the frontend image reference on the command line: ```console $ docker build --build-arg BUILDKIT_SYNTAX=docker/dockerfile:1 . ``` This defines the location of the Dockerfile syntax that is used to build the Dockerfile. The BuildKit backend allows seamlessly using external implementations that are distributed as Docker images and execute inside a container sandbox environment. Custom Dockerfile implementations allow you to: - Automatically get bug fixes without updating the Docker daemon - Make sure all users are using the same implementation to build your Dockerfile - Use the latest features without updating the Docker daemon - Try out new features or third-party features before they are integrated in the Docker daemon - Use [alternative build definitions, or create your own](https://github.com/moby/buildkit#exploring-llb) - Build your own Dockerfile frontend with custom features > [!NOTE] > > BuildKit ships with a built-in Dockerfile frontend, but it's recommended > to use an external image to make sure that all users use the same version on > the builder and to pick up bug fixes automatically without waiting for a new > version of BuildKit or Docker Engine. ## Official releases Docker distributes official versions of the images that can be used for building Dockerfiles under `docker/dockerfile` repository on Docker Hub. There are two channels where new images are released: `stable` and `labs`. ### Stable channel The `stable` channel follows [semantic versioning](https://semver.org). For example: - `docker/dockerfile:1` - kept updated with the latest `1.x.x` minor _and_ patch

BuildKit allows dynamically loading frontends from container images using the `syntax` directive in the Dockerfile. This enables using external Dockerfile implementations distributed as Docker images, offering benefits like automatic bug fixes, consistent builds, access to the latest features, and the ability to experiment with new or third-party features. Docker provides official Dockerfile images under the `docker/dockerfile` repository, with `stable` and `labs` channels for releases.