Unable to use Buildkit with Windows containers

[tofflos]

I'm using the Buildkit version that comes bundled with Docker for Windows 18.06.1 and am experiencing some trouble running it with Windows containers. In the log below you can see a build succeed for a very simple build running without Buildkit and then failing once I enable it. The localized error message "Det går inte att hitta filen" roughly translates to "Unable to find the file". I've had success running Buildkit on the same system when running Linux containers. A minimal project that reproduces the error can be found here test.zip.

PS C:\test> docker version
Client:
 Version:           18.06.1-ce
 API version:       1.38
 Go version:        go1.10.3
 Git commit:        e68fc7a
 Built:             Tue Aug 21 17:21:34 2018
 OS/Arch:           windows/amd64
 Experimental:      false

Server:
 Engine:
  Version:          18.06.1-ce
  API version:      1.38 (minimum version 1.24)
  Go version:       go1.10.3
  Git commit:       e68fc7a
  Built:            Tue Aug 21 17:36:40 2018
  OS/Arch:          windows/amd64
  Experimental:     true
PS C:\test> ls


    Directory: C:\test


Mode                LastWriteTime         Length Name
----                -------------         ------ ----
-a----       2018-09-11     15:38             74 Dockerfile
-a----       2018-09-11     15:39             23 test.txt


PS C:\test> type .\Dockerfile
FROM microsoft/nanoserver:1803
COPY test.txt /test.txt
RUN type test.txt

PS C:\test> $Env:DOCKER_BUILDKIT=0
PS C:\test> docker build -t test .
Sending build context to Docker daemon  3.072kB
Step 1/3 : FROM microsoft/nanoserver:1803
 ---> 693ff1719e39
Step 2/3 : COPY test.txt /test.txt
 ---> 3cb8bc9e5e2e
Step 3/3 : RUN type test.txt
 ---> Running in 376f873629fd
This is a test message!Removing intermediate container 376f873629fd
 ---> 0cce47564a2d
Successfully built 0cce47564a2d
Successfully tagged test:latest

PS C:\test> $Env:DOCKER_BUILDKIT=1
PS C:\test> docker build -t test .
[+] Building 0.2s (2/2) FINISHED
 => local://dockerfile (Dockerfile)                                                                                                                                                                                                                                       0.1s
 => => transferring dockerfile: 31B                                                                                                                                                                                                                                       0.0s
 => local://context (.dockerignore)                                                                                                                                                                                                                                       0.1s
 => => transferring context: 2B                                                                                                                                                                                                                                           0.0s
failed to read dockerfile: open C:\ProgramData\Docker\tmp\buildkit-mount977689469\Dockerfile: Det går inte att hitta filen.

[tonistiigi]

Buildkit is not supported for Windows containers in docker 18.06/18.09

[gerich-home]

Any plans to support it?

[quangkieu]

If there is no windows container support yet, I think the error message need to be update to define expectation.

[olljanat]

@quangkieu it looks to be described on documentation: https://docs.docker.com/build/buildkit/#getting-started
Only supported for building Linux containers

[quangkieu]

@olljanat I meant about the error message from the built process.

[Rick-van-Dam]

When is buildkit support coming for windows?

[TBBle]

Maybe a better question is what needs to be done/what are the outstanding dependencies?

[Iristyle]

Has anyone tried using buildctl on Windows via instructions at https://github.com/moby/buildkit#exploring-dockerfiles with buildkit daemon running in a container? Looks like that might be an alternative until docker build works properly on Windows?

[olljanat]

@Iristyle if you read that doc more carefully it also says

the buildkitd daemon is only available for Linux currently.

@Barsonax I'm bit worry about that we will not see Windows containers support ever because there is no Microsoft persons contributin to this project. Hopefully I'm wrong.

[Iristyle]

@olljanat well, I'm using LCOW, which hosts a real Linux kernel - so it's a bit of a grey area (and a lot of the docker folks don't seem to know much about in practical terms). I played around a little and I was getting closer to having rootless running per instructions at https://github.com/moby/buildkit/blob/master/docs/rootless.md#about---oci-worker-no-process-sandbox, noting that --privileged is not supported on Windows at all.

I'll update if I'm able to get it going or hit a dead end.

[olljanat]

@Iristyle that is probably possible but this issue is about real Windows containers so let's try keep on topic.

[TBBle]

Since last time I looked into this, containerd gained support for Windows 10 1809/Windows Server 2019, so it's possible no MS involvement in buildkit is needed, if it can get everything it needs for the low-level part via its containerd backend.

Edit: A quick look at the build system for buildkit suggests that you need running buildkit (either locally, or running inside Docker) to build buildkit. I'm somewhat flummoxed by this.