ACK, taking a look.

Attempting to build an image for WCOW from a custom frontend using BuildKit will result to error you got (ERROR: failed to solve: hcsshim::ProcessBaseLayer ....) if the custom frontend contains no base layer.

I created a new custom frontend with a NanoServer image as the base layer, but ended up encountering the error below.

  PS E:\repro-4892> docker buildx build .
[+] Building 1.3s (4/4) FINISHED                                                                                      remote:buildkit-exp
 => [internal] load build definition from Dockerfile                                                                                 0.1s
 => => transferring dockerfile: 80B                                                                                                  0.0s
 => resolve image config for docker-image://docker.io/100909/dockerfile-4892:latest                                                  0.4s
 => [auth] 100909/dockerfile-4892:pull token for registry-1.docker.io                                                                0.0s
 => CACHED docker-image://docker.io/100909/dockerfile-4892:latest@sha256:483bf8f1796a24323c1ea215016297988326afb84ddc97312e0fd17b7c  0.0s
 => => resolve docker.io/100909/dockerfile-4892:latest@sha256:483bf8f1796a24323c1ea215016297988326afb84ddc97312e0fd17b7caeb5ca       0.0s
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:1
--------------------
   1 | >>> # syntax=docker.io/100909/dockerfile-4892
   2 |
--------------------
**

ERROR: failed to solve: failed to create shim task: invalid OCI spec - Type 'bind' not supported: unknown

**
View build details: docker-desktop://dashboard/build/buildkit-exp/buildkit-exp0/0gzd6kdf2hllfq7ygzllikkm2

------------

Investigations into the containerd and hcsshim source codes indicate that containerd passes 'windows-layer' as the mount type to hscshim. I suspect that hscshim could be generating predefined mount types (yet to ascertain this).

Any idea of the valid Mount Types for this case?

/cc. @gabriel-samfira

Attempting to build an image for WCOW from a custom frontend using BuildKit will result to error you got (ERROR: failed to solve: hcsshim::ProcessBaseLayer ....) if the custom frontend contains no base layer.

I created a new custom frontend with a NanoServer image as the base layer, but ended up encountering the error below.

  PS E:\repro-4892> docker buildx build .
[+] Building 1.3s (4/4) FINISHED                                                                                      remote:buildkit-exp
 => [internal] load build definition from Dockerfile                                                                                 0.1s
 => => transferring dockerfile: 80B                                                                                                  0.0s
 => resolve image config for docker-image://docker.io/100909/dockerfile-4892:latest                                                  0.4s
 => [auth] 100909/dockerfile-4892:pull token for registry-1.docker.io                                                                0.0s
 => CACHED docker-image://docker.io/100909/dockerfile-4892:latest@sha256:483bf8f1796a24323c1ea215016297988326afb84ddc97312e0fd17b7c  0.0s
 => => resolve docker.io/100909/dockerfile-4892:latest@sha256:483bf8f1796a24323c1ea215016297988326afb84ddc97312e0fd17b7caeb5ca       0.0s
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:1
--------------------
   1 | >>> # syntax=docker.io/100909/dockerfile-4892
   2 |
--------------------
**

ERROR: failed to solve: failed to create shim task: invalid OCI spec - Type 'bind' not supported: unknown

**
View build details: docker-desktop://dashboard/build/buildkit-exp/buildkit-exp0/0gzd6kdf2hllfq7ygzllikkm2

------------

Investigations into the containerd and hcsshim source codes indicate that containerd passes 'windows-layer' as the mount type to hscshim. I suspect that hscshim could be generating predefined mount types (yet to ascertain this).

Any idea of the valid Mount Types f

Attempting to build an image for WCOW from a custom frontend using BuildKit will result to error you got (ERROR: failed to solve: hcsshim::ProcessBaseLayer ....) if the custom frontend contains no base layer.

I created a new custom frontend with a NanoServer image as the base layer, but ended up encountering the error below.

  PS E:\repro-4892> docker buildx build .
[+] Building 1.3s (4/4) FINISHED                                                                                      remote:buildkit-exp
 => [internal] load build definition from Dockerfile                                                                                 0.1s
 => => transferring dockerfile: 80B                                                                                                  0.0s
 => resolve image config for docker-image://docker.io/100909/dockerfile-4892:latest                                                  0.4s
 => [auth] 100909/dockerfile-4892:pull token for registry-1.docker.io                                                                0.0s
 => CACHED docker-image://docker.io/100909/dockerfile-4892:latest@sha256:483bf8f1796a24323c1ea215016297988326afb84ddc97312e0fd17b7c  0.0s
 => => resolve docker.io/100909/dockerfile-4892:latest@sha256:483bf8f1796a24323c1ea215016297988326afb84ddc97312e0fd17b7caeb5ca       0.0s
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:1
--------------------
   1 | >>> # syntax=docker.io/100909/dockerfile-4892
   2 |
--------------------
**

ERROR: failed to solve: failed to create shim task: invalid OCI spec - Type 'bind' not supported: unknown

**
View build details: docker-desktop://dashboard/build/buildkit-exp/buildkit-exp0/0gzd6kdf2hllfq7ygzllikkm2

------------

Investigations into the containerd and hcsshim source codes indicate that containerd passes 'windows-layer' as the mount type to hscshim. I suspect that hscshim could be generating predefined mount types (yet to ascertain this).

Any idea of the valid Mount Types for this case?

this issues was resolved.... no longer needs feedback

@pl4nty if you dont mind can share the dockerfile for this image ghcr.io/pl4nty/dockerfile:master
alternatively push the image to docker reg, would wish test it, I am currently working on this wcow custom frontends issue, publishing PR soon, but wished also to test my changes using your scenario

@billywr the Dockerfile is frontend/dockerfile/cmd/dockerfile-frontend/Dockerfile with the changes I provided, pushed to ghcr.io/pl4nty/dockerfile:master

Thank you for the reply.

I don't think the changes you made to the Dockerfile would result in a working WCOW custom docker frontend, since the Dockerfile references non-WCOW base images—unless you were specifically testing Linux containers on Windows.

I'm currently working on this PR, where I'll be updating the steps I used to create a sample custom frontend for WCOW. I would really appreciate your input on it.

I was building on a Linux host, and since the output Windows image is FROM scratch with a single COPY, I thought it was supported. But I now see the entrypoint is /bin/dockerfile-frontend, is this path format supported on WCOW?

no, should be something like , ENTRYPOINT ["C:\dockerfile-frontend.exe"]
also SCRATCH is not yet supported,
also ensure you are using windows base image , like in place of alpine you can have mcr.microsoft.com/windows/nanoserver:ltsc2022