buildx is a Docker CLI plugin for extended build capabilities with
BuildKit.
Key features:
- Familiar UI from
docker build - Full BuildKit capabilities with container driver
- Multiple builder instance support
- Multi-node builds for cross-platform images
- Compose build support
- High-level build constructs (
bake) - In-container driver support (both Docker and Kubernetes)
Using buildx as a docker CLI plugin requires using Docker 19.03 or newer.
A limited set of functionality works with older versions of Docker when
invoking the binary directly.
buildx comes bundled with Docker Desktop and in latest
Docker CE packages, but may not be
included in third-party software components (in which case follow the
binary release instructions).
You can also download the latest buildx binary from the
GitHub releases page, copy
it to ~/.docker/cli-plugins folder with name docker-buildx and change the
permission to execute:
$ chmod a+x ~/.docker/cli-plugins/docker-buildxHere is how to use buildx inside a Dockerfile through the
docker/buildx-bin image:
FROM docker
COPY --from=docker/buildx-bin /buildx /usr/libexec/docker/cli-plugins/docker-buildx
RUN docker buildx versionRunning the command docker buildx install
sets up docker builder command as an alias to docker buildx build. This
results in the ability to have docker build use the current buildx builder.
To remove this alias, run docker buildx uninstall.
# Buildx 0.6+
$ docker buildx bake "git://github.com/docker/buildx"
$ mkdir -p ~/.docker/cli-plugins
$ mv ./bin/buildx ~/.docker/cli-plugins/docker-buildx
# Docker 19.03+
$ DOCKER_BUILDKIT=1 docker build --platform=local -o . "git://github.com/docker/buildx"
$ mkdir -p ~/.docker/cli-plugins
$ mv buildx ~/.docker/cli-plugins/docker-buildx
# Local
$ git clone git://github.com/docker/buildx && cd buildx
$ make installBuildx is a Docker CLI plugin that extends the docker build command with the
full support of the features provided by Moby BuildKit
builder toolkit. It provides the same user experience as docker build with
many new features like creating scoped builder instances and building against
multiple nodes concurrently.
After installation, buildx can be accessed through the docker buildx command
with Docker 19.03. docker buildx build is the command for starting a new
build. With Docker versions older than 19.03 buildx binary can be called
directly to access the docker buildx subcommands.
$ docker buildx build .
[+] Building 8.4s (23/32)
=> ...Buildx will always build using the BuildKit engine and does not require
DOCKER_BUILDKIT=1 environment variable for starting builds.
The docker buildx build command supports features available for docker build,
including features such as outputs configuration, inline build caching, and
specifying target platform. In addition, Buildx also supports new features that
are not yet available for regular docker build like building manifest lists,
distributed caching, and exporting build results to OCI image tarballs.
Buildx is supposed to be flexible and can be run in different configurations
that are exposed through a driver concept. Currently, we support a
docker driver that uses
the BuildKit library bundled into the Docker daemon binary, a
docker-container driver
that automatically launches BuildKit inside a Docker container and a
kubernetes driver to
spin up pods with defined BuildKit container image to build your images. We
plan to add more drivers in the future.
The user experience of using buildx is very similar across drivers, but there
are some features that are not currently supported by the docker driver,
because the BuildKit library bundled into docker daemon currently uses a
different storage component. In contrast, all images built with docker driver
are automatically added to the docker images view by default, whereas when
using other drivers the method for outputting an image needs to be selected
with --output.
By default, buildx will initially use the docker driver if it is supported,
providing a very similar user experience to the native docker build. Note tha
you must use a local shared daemon to build your applications.
Buildx allows you to create new instances of isolated builders. This can be used for getting a scoped environment for your CI builds that does not change the state of the shared daemon or for isolating the builds for different projects. You can create a new instance for a set of remote nodes, forming a build farm, and quickly switch between them.
You can create new instances using the docker buildx create
command. This creates a new builder instance with a single node based on your
current configuration.
To use a remote node you can specify the DOCKER_HOST or the remote context name
while creating the new builder. After creating a new instance, you can manage its
lifecycle using the docker buildx inspect,
docker buildx stop, and
docker buildx rm commands. To list all
available builders, use buildx ls. After
creating a new builder you can also append new nodes to it.
To switch between different builders, use docker buildx use <name>.
After running this command, the build commands will automatically use this
builder.
Docker also features a docker context
command that can be used for giving names for remote Docker API endpoints.
Buildx integrates with docker context so that all of your contexts
automatically get a default builder instance. While creating a new builder
instance or when adding a node to it you can also set the context name as the
target.
BuildKit is designed to work well for building for multiple platforms and not only for the architecture and operating system that the user invoking the build happens to run.
When you invoke a build, you can set the --platform flag to specify the target
platform for the build output, (for example, linux/amd64, linux/arm64, or
darwin/amd64).
When the current builder instance is backed by the docker-container or
kubernetes driver, you can specify multiple platforms together. In this case,
it builds a manifest list which contains images for all specified architectures.
When you use this image in docker run
or docker service,
Docker picks the correct image based on the node's platform.
You can build multi-platform images using three different strategies that are supported by Buildx and Dockerfiles:
- Using the QEMU emulation support in the kernel
- Building on multiple native nodes using the same builder instance
- Using a stage in Dockerfile to cross-compile to different architectures
QEMU is the easiest way to get started if your node already supports it (for
example. if you are using Docker Desktop). It requires no changes to your
Dockerfile and BuildKit automatically detects the secondary architectures that
are available. When BuildKit needs to run a binary for a different architecture,
it automatically loads it through a binary registered in the binfmt_misc
handler.
For QEMU binaries registered with binfmt_misc on the host OS to work
transparently inside containers they must be registered with the fix_binary
flag. This requires a kernel >= 4.8 and binfmt-support >= 2.1.7. You can check
for proper registration by checking if F is among the flags in
/proc/sys/fs/binfmt_misc/qemu-*. While Docker Desktop comes preconfigured
with binfmt_misc support for additional platforms, for other installations
it likely needs to be installed using tonistiigi/binfmt
image.
$ docker run --privileged --rm tonistiigi/binfmt --install allUsing multiple native nodes provide better support for more complicated cases
that are not handled by QEMU and generally have better performance. You can
add additional nodes to the builder instance using the --append flag.
Assuming contexts node-amd64 and node-arm64 exist in docker context ls;
$ docker buildx create --use --name mybuild node-amd64
mybuild
$ docker buildx create --append --name mybuild node-arm64
$ docker buildx build --platform linux/amd64,linux/arm64 .Finally, depending on your project, the language that you use may have good
support for cross-compilation. In that case, multi-stage builds in Dockerfiles
can be effectively used to build binaries for the platform specified with
--platform using the native architecture of the build node. A list of build
arguments like BUILDPLATFORM and TARGETPLATFORM is available automatically
inside your Dockerfile and can be leveraged by the processes running as part
of your build.
FROM --platform=$BUILDPLATFORM golang:alpine AS build
ARG TARGETPLATFORM
ARG BUILDPLATFORM
RUN echo "I am running on $BUILDPLATFORM, building for $TARGETPLATFORM" > /log
FROM alpine
COPY --from=build /log /logYou can also use tonistiigi/xx Dockerfile
cross-compilation helpers for more advanced use-cases.
Buildx also aims to provide support for high-level build concepts that go beyond invoking a single build command. We want to support building all the images in your application together and let the users define project specific reusable build flows that can then be easily invoked by anyone.
BuildKit efficiently handles multiple concurrent build requests and
de-duplicating work. The build commands can be combined with general-purpose
command runners (for example, make). However, these tools generally invoke
builds in sequence and therefore cannot leverage the full potential of BuildKit
parallelization, or combine BuildKit’s output for the user. For this use case,
we have added a command called docker buildx bake.
The bake command supports building images from compose files, similar to
docker-compose build,
but allowing all the services to be built concurrently as part of a single
request.
There is also support for custom build rules from HCL/JSON files allowing better code reuse and different target groups. The design of bake is in very early stages and we are looking for feedback from users.
Want to contribute to Buildx? Awesome! You can find information about contributing to this project in the CONTRIBUTING.md