WCOW: RUN with bind/cache mounts

[danielnilsson9]

I have been doing some testing with windows container builds recently.

I have been trying to figure out it cache/bind mounts are supposed to work or not.
I have found this issue: #4837 Maybe the underlaying cause is the same even though the error message is different?

Environment
Windows Server 2022
Builkit 0.18.1
Containerd 1.7.24

Dockerfile

FROM mcr.microsoft.com/windows/nanoserver:ltsc2022

USER ContainerAdministrator
WORKDIR C:/BUILD/
RUN --mount=type=cache,target=C:/BUILD/ echo "Hello" >> hello.txt

Output

buildx build --progress=plain .
#0 building with "windows" instance using remote driver

#1 [internal] load build definition from Dockerfile
#1 transferring dockerfile: 208B done
#1 DONE 0.1s

#2 [internal] load metadata for mcr.microsoft.com/windows/nanoserver:ltsc2022
#2 DONE 0.1s

#3 [internal] load .dockerignore
#3 transferring context:
#3 transferring context: 2B done
#3 DONE 1.2s

#4 [stage-0 1/3] FROM mcr.microsoft.com/windows/nanoserver:ltsc2022@sha256:eb59dfa1056e41b65cb12b679280e29f10d64e2b569b877710e227a77fef223f
#4 resolve mcr.microsoft.com/windows/nanoserver:ltsc2022@sha256:eb59dfa1056e41b65cb12b679280e29f10d64e2b569b877710e227a77fef223f 0.0s done
#4 DONE 0.0s

#5 [stage-0 2/3] WORKDIR C:/TEMP/
#5 CACHED

#6 [stage-0 3/3] RUN --mount=type=cache,target=C:/TEMP/ echo "Hello" >> hello.txt
#6 ERROR: process "cmd /S /C echo \"Hello\" >> hello.txt" did not complete successfully: failed to create shim task: invalid OCI spec - Type 'windows-layer' not supported: unknown
------
 > [stage-0 3/3] RUN --mount=type=cache,target=C:/TEMP/ echo "Hello" >> hello.txt:
------
WARNING: No output specified with remote driver. Build result will only remain in the build cache. To push result image into registry use --push or to load image into docker use --load
Dockerfile:7
--------------------
   5 |     WORKDIR C:/TEMP/
   6 |
   7 | >>> RUN --mount=type=cache,target=C:/TEMP/ echo "Hello" >> hello.txt
--------------------
ERROR: failed to solve: process "cmd /S /C echo \"Hello\" >> hello.txt" did not complete successfully: failed to create shim task: invalid OCI spec - Type 'windows-layer' not supported: unknown

Is this the expected result or have I possibly done something wrong?

[profnandaa]

You are right, they are related. I'm currently investigating how to support this, I will update.