Estimated reading time: 8 minutes
Docker Buildx is a CLI plugin that extends the docker 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.
Docker Buildx is included in Docker Desktop and Docker Linux packages when installed using the DEB or RPM packages.
You can also download the latest
buildx binary from the
Docker buildx releases page
on GitHub, copy it to
~/.docker/cli-plugins folder with name
docker-buildx and change the permission to execute:
$ chmod a+x ~/.docker/cli-plugins/docker-buildx
Here is how to use buildx inside a Dockerfile through the
FROM docker COPY --from=docker/buildx-bin /buildx /usr/libexec/docker/cli-plugins/docker-buildx RUN docker buildx version
Set buildx as the default builder
To remove this alias, run
docker buildx uninstall.
Build with buildx
To start a new build, run the command
docker buildx build .
$ docker buildx build . [+] Building 8.4s (23/32) => ...
Buildx builds using the BuildKit engine and does not require
environment variable to start the builds.
docker buildx build command supports features available for
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.
You can run Buildx in different configurations that are exposed through a driver concept. Currently, Docker supports a “docker” driver that uses the BuildKit library bundled into the Docker daemon binary, and a “docker-container” driver that automatically launches BuildKit inside a Docker container.
The user experience of using Buildx is very similar across drivers. However,
there are some features that are not currently supported by the “docker” driver,
because the BuildKit library which is bundled into docker daemon uses a different
storage component. In contrast, all images built with the “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
Work with builder instances
By default, Buildx uses the
docker driver if it is supported, providing a user
experience very similar to the native
docker build. Note that you must use a
local shared daemon to build your applications.
Buildx allows you to create new instances of isolated builders. You can use this to get a scoped environment for your CI builds that does not change the state of the shared daemon, or for isolating 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
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
docker 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
Docker also features a
command that you can use to provide names for remote Docker API endpoints. Buildx
docker context to ensure all the contexts automatically get a
default builder instance. You can also set the context name as the target when
you create a new builder instance or when you add a node to it.
Build multi-platform images
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,
When the current builder instance is backed by the
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
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
For QEMU binaries registered with
binfmt_misc on the host OS to work
transparently inside containers they must be registered with the
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
binfmt_misc support for additional platforms, for other installations
it likely needs to be installed using
$ docker run --privileged --rm tonistiigi/binfmt --install all
Using 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
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
TARGETPLATFORM is available automatically
inside your Dockerfile and can be leveraged by the processes running as part
of your build.
# syntax=docker/dockerfile:1 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 /log
High-level build options
Buildx also aims to provide support for high-level build concepts that go beyond invoking a single build command.
BuildKit efficiently handles multiple concurrent build requests and de-duplicating
work. The build commands can be combined with general-purpose command runners
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
docker buildx bake.
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. Let us know your feedback by creating an issue in the Docker buildx GitHub repository.Docker, buildx, multi-arch