Docker now has multi-platform builds via BuildKit (the buildx subcommand). For folks, like myself, working on a Macbook running Apple Silicon, this is both a blessing and a curse. It's a blessing because it makes it possible to build linux/amd64 images even though I'm running on an ARM CPU. It's a curse because it's a complicated Inception-esque stack of virtualization. buildimg is a simple command I use to automate building and publishing multi-platform images. In particular, I have a number of projects where the containers run on linux/amd64 but are developed on my laptop, which natively produces linux/arm64.
buildimg is a plain ole Go and can be installed using go install kind of like this:
go install github.com/kellegous/buildimg@latest
The best way to explain how buildimg works is to just look at some examples.
The following command will build and push a new linux/amd64 image for kellegous/example. The tag for the build will be determined from the git directory in the current working directory and so this will push an image that looks similar to kellegous/exmaple:2193a7f6.
$ buildimg --target=linux/amd64 kellegous/example
The next example is similar except it will push both a linux/amd64 image and a linux/arm64 image. Like the previous command, the image will be tagged with the latest SHA from the git directory in the current working directory.
$ buildimg --target=linux/amd64 --target=linux/arm64 kellegous/example
Next, instead of relying on git for the tag, let's explicitly tag the image with latest.
$ buildimg --target=linux/amd64 --target=linux/arm64 --tag=latest kellegous/example
What if we do not wish to push the images at all? The following command will build a linux/amd64 image and export it to the file example-amd64.tar. That file can be imported into docker via docker import as it follows the OCI Image Layout.
$ buildimg --target=linux/amd64:example-amd64.tar kellegous/example
Again, multiple --target flags can be specified, each with a destination file that allows one to create a multi-platform build where each platform is saved in an OCI image tarball. For instance, this command creates linux/amd64 build and stores it in example-amd64.tar and also creates a linux/arm64 build and stores it in the file example-arm64.tar.
$ buildimg --target=linux/amd64:example-amd64.tar --target=linux/arm64:example-arm64.tar kellegous/example
Generally, any target that specifies a destination path (i.e. linux/arm64:example.tar) will be exported to a local tarbar and any target that does not specify a destination path will be pushed. So for instance, the following command exports a linux/arm64 build to the local file example.tar and also pushes a linux/amd64 build to the docker.io registry.
$ buildimg --target=linux/arm64:example.tar --target=linux/amd64 kellegous/example
Note that it is possible to push a particular platform and also export it locally with the same command. In this example, a linux/amd64 image is both pushed to the docker.io registry and exported locally to the file example.tar.
$ buildimg --target=linux/amd64 --target=linux/amd64:example.tar kellegous/example
- Kelly Norton kellegous.com