Tracking Windows buildkit required features

[junglie85]

Experimental Windows support was released in version 0.13.0 of buildkit and details of how to use are in a blog entry.

This is a great step on the way to being able to unify Windows and Linux build processes.

What are the missing features in buildkit that are needed before unification can happen? Perhaps we could track them in this issue?

Required features:

• --secret flag, see Windows docker container buildctl does not allow mounting secrets. It fails mounting to linux tmpfs location moby/buildkit#5273
• cache mounts

Nice to have features:

• buildkit support implemented for docker buildx build instead of manually calling containerd and buildkitd

[slonopotamus]

I'm not sure we want to directly call buildkitd. Instead, it would be much more convenient if Windows + buildkit support was implemented for docker buildx build (that we already use and would just need to adjust our code a little: https://github.com/moby/moby/blob/v27.3.1/builder/builder-next/executor_nolinux.go#L25)

[TBBle]

Well, then we can mark down "integration into buildx" as an example of a feature we're waiting for, which is mostly in the moby builder-next support, or alternatively if someone gets the docker-container or one of the remote drivers working, that'd work too.

Off-hand, the only other thing that we care about that is new in buildx is the --secret flag, i.e. moby/buildkit#5273 says that's not available yet, and AFAIR that's our primary motivator for using buildx/BuildKit.

[slonopotamus]

the only other thing that we care about that is new in buildx is the --secret flag

We also care about cache-mounts that only work with buildkit.

[TBBle]

Good point. As it happens, that's the same ticket, I suspect, in the general sense of "Get everything in https://github.com/moby/buildkit/blob/master/solver/llbsolver/mounts/mount.go working on WIndows". I'm not sure how cache mounts work at the implementation level, but all the other mounts in that file currently utilise tmpfs in some way or other, and we don't have a Windows equivalent for that AFAIK.

[slonopotamus]

I believe cache mounts are just binds.

[junglie85]

I'm not sure we want to directly call buildkitd.

I'm hopeful that longer term this wouldn't be needed. But I don't see why ue4-docker would need to directly call buildkitd. Until buildkit is better integrated into Docker on Windows, starting containerd and buildkitd, and creating a builder could be a pre-requesite to running ue4-dockeer.

the only other thing that we care about that is new in buildx is the --secret flag, i.e. moby/buildkit#5273

This is probably a bigger blocker, given the statement that they don't plan to implement this until the classic builder has feature parity.

I believe cache mounts are just binds.

I can't find confirmation of this in the docs. @slonopotamus do you know where this can be confirmed?