Docker is a wonderful tool for packaging applications for easy deployment into a variety of environments. I personally have been experimenting with a Docker Swarm at home on a number of Raspberry Pis. It’s been a great learning experience, and I am constantly amazed by what can be done with a $35 computer. The issue I encountered very quickly was that I could usually find an image of an application on Docker Hub, but it was often only built for amd64 architectures which will not run on the Raspberry Pi’s arm/v7. Luckily, Docker has a built in utility (starting with 19.03) called Docker BuildKit (buildx) which allows for building images for alternative architectures from the machine building the image.


First install Docker on your system. The Docker website has a number of gudies and instructions to accomplish this. Now, before you can start using Buildx you will need to enable experimental features in the config. On Windows and Mac there is a checkbox in the application to enable Experimental. On Linux, open ~/.docker/config.json in the text editor of your choosing. If it doesn’t exist you will need to make it. Place the following in the file.

    "experimental": "enabled"

After that, restart Docker. You should now get a usage output in your terminal when typing docker buildx. Running docker buildx ls will show you all available builders and the architectures they are able to build for. For now you should see a default builder only capable of building for your systems architecture.


To be able to build for multiple architectures we need to create a builder that includes the needed QEMU binfmt binaries. We can create a new builder by running

docker buildx create --name xbuilder

The name is for convience only, so you can use whatever name you prefer. This will create the builder, but not set it for use. To do that you need to run

docker buildx use xbuilder

Now, when you call a buildx command the specified one will be used. As of right now it does not have the ability to build for the other architectures. To do that we need to run a docker image that contains the binfmt binaries in privileged mode to allow the builder access to them.

docker run --rm --privileged linuxkit/binfmt:v0.8 #latest as of writing

Now with all the other parts in place we can start our builder. This will make it ready for use

docker buildx inspect --bootstrap

You can verify that everything started correctly by running docker buildx ls again. You should now see xbuilder listed as one of the builders and a long list of available platforms.


Building images with BuildKit is not much different from building a regular image with Docker. The biggest difference being that you need to specify the architectures you want to build for your Dockerfile. A simple build command would look like

docker buildx build --platform=linux/amd64,linux/arm/v7,linux/arm64 --push -t jdreinhardt/test:latest .

In this example I am building for amd64 which is most computers, arm/v7 which is most SBC including the Raspberry Pi, and arm64 which is found on newer SBCs including the Pi 4. --push specifies that the resulting images are to be pushed to Docker Hub using the tags, -t, specified. If you wish to build locally only you can use --load instead which will copy the resulting image out of the builder and to your local system. This does have the limitation that only one architecture can be specified using platform.

There is plenty more to learn, but this should get you started on building Dockerfiles for multiple architectures without the need for multiple devices.