Docker BuildKit

BuildKit is the abstracted and improved version of the container image builder that is (used to be?) shipped with docker(8).

Contents

Docker BuildKit
1. Installation
2. Usage
  1. Contexts

Installation

In vertsion 23, the legacy builder for Docker images was deprecated. The deprecation message is as follows:

DEPRECATED: The legacy builder is deprecated and will be removed in a future release.
            Install the buildx component to build images with BuildKit:
            https://docs.docker.com/go/buildx/

BuildKit (also known as buildx) is now the only supported builder. Users must opt in by setting DOCKER_BUILDKIT=1. Removal of the legacy builder has not yet been scheduled.

Users may also need to install the buildx plugin separately. This error would appear as:

ERROR: BuildKit is enabled but the buildx component is missing or broken.
       Install the buildx component to build images with BuildKit:
       https://docs.docker.com/go/buildx/

On Arch, install docker-buildx.

Usage

docker build .

Contexts

BuildKit supports building in an isolated context (i.e., inside a container). Try:

$ docker buildx create --name my-builder --driver docker-container --bootstrap --use
$ docker buildx ls
NAME/NODE         DRIVER/ENDPOINT                   STATUS    BUILDKIT   PLATFORMS
my-builder*       docker-container                                       
 \_ my-builder0    \_ unix:///var/run/docker.sock   running   v0.25.1    linux/amd64 (+3), linux/arm64, linux/arm (+2), linux/ppc64le, (7 more)
default           docker                                                 
 \_ default        \_ default                       running   v0.25.1    linux/amd64 (+3), linux/arm64, linux/arm (+2), linux/ppc64le, (7 more)

One important advantage to this system is building multi-platform images.

docker buildx build --platform=linux/amd64,linux/arm64 .

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