Native builder required for targeting different ARCH

[jahkeup]

Image I'm using:

n/a

Issue and Feature Request:

The build process is unable to produce an arm64v8 architecture specific image. The build's Dockerfile uses a scratch based container image and, on my machine at least, the requested architecture is not set for this image (with ARCH=arm64).

docker build uses the native architecture for scratch and does not support setting platform in builder. Using Docker's buildx works when setting platform at the top of the build:

docker buildx build --platform linux/arm64 ... # existing arguments

However, this would require users to install the buildx plugin and isn't a reasonable ask.

This issue should define a solution towards a correctly building a non-native architecture targeted image OR take steps to set the image's correct architecture at/following build.

[cbgbt]

We've investigated this issue and found that, at the time, there doesn't seem to be a way to convince docker to change the architecture of a resulting image, other than through buildx. This was through research in late 2021, so it may have changed now. Worth keeping this issue in the backlog, as this would be a really useful feature.

[stmcginnis]

FWIW, I think buildx is more prevalent now than when this issue was created, and is the de facto way to be able to build cross architecture images. So I think it would be perfectly reasonable to update things to use buildx.

[jpculp]

For what it's worth, we also made updates to the admin and control container Dockerfiles to be compatible with buildx, although we still don't use it in the Makefiles.

[jpmcb]

FWIW, I think buildx is more prevalent now than when this issue was created, and is the de facto way to be able to build cross architecture images. So I think it would be perfectly reasonable to update things to use buildx.

I actually looked at this abit when I went down the rabbit hole of arm builds for bottlerocket and testsys (see bottlerocket-os/bottlerocket-test-system#90 & bottlerocket-os/bottlerocket-test-system#509)

But I quickly discovered a roadblock; our bottlerocket SDK's manifest is not multi-arch. So attempting to build a multiarch manifest from a single docker target (instead, it uses a build-arg to determine the architecture and then pushes a separate image per arch.)

So, there may be changes to happen in dependent images (aka, the SDK) to make this possible.