dotnet publish inside Dockerfile doesn't work on 8.0-alpine

[rcdailey]

I'm referencing the sample [here]. For my personal project, I have this in the build portion of my Dockerfile:

# syntax=docker/dockerfile:1.7-labs

# Following Microsoft's pattern shown here:
# https://github.com/dotnet/dotnet-docker/blob/main/samples/dotnetapp/Dockerfile.alpine
# https://github.com/dotnet/dotnet-docker/blob/main/samples/README.md
#
FROM --platform=$BUILDPLATFORM mcr.microsoft.com/dotnet/sdk:8.0-alpine AS build

ARG TARGETARCH
WORKDIR /source

# copy csproj and restore as distinct layers
COPY --parents *.props src/*/*.csproj ./
RUN dotnet restore src/Recyclarr.Cli -a $TARGETARCH

# copy and publish app and libraries
COPY . .
RUN dotnet publish src/Recyclarr.Cli -a $TARGETARCH --no-restore -o /app

You can find this and more in my open source repo here.

When I run docker compose build, I get this error message during the dotnet publish step:

error NETSDK1047: Assets file '/source/src/Recyclarr.Cli/obj/project.assets.json' doesn't have a target for 'net8.0/linux-musl-x64'. Ensure that restore has run and that you have included 'net8.0' in the TargetFrameworks for your project. You may also need to include 'linux-musl-x64' in your project's RuntimeIdentifiers.

As far as I can tell, I'm doing exactly what the sample is doing. I also added the -v d argument to the dotnet restore command to see more verbose output. It does indeed show linux-musl-x64 being used to restore packages.

I'm completely lost here. What am I doing wrong?

[MichaelSimons]

Do you have a .dockerignore? The COPY . . can be interfering if you don't and you have built locally. From https://learn.microsoft.com/en-us/dotnet/core/tools/sdk-errors/netsdk1005

If you're building a Docker image, make sure the .dockerignore file ignores the bin and obj directories. For more information, see GitHub pull request dotnet/docs #29530.

[rcdailey]

I do not have a .dockerignore, so that's most likely the issue. I feel like .dockerignore is redundant when I have .gitignore; very frustrating that I have to add it. I do appreciate your help.

[rcdailey]

I tested this and indeed it does work. The .dockerignore was an oversight on my part, mainly because I was hyper-focused on the README.md. I think it might help to mention the importance of the .dockerignore in the readme itself. This one, for example, doesn't mention it at all. A warning-style admonition to make something like this catch people's eye would have helped me, at least!

Thank you again for your help.

[MichaelSimons]

Please feel free to open an issue and/or PR to help improve the READMEs.

[richlander]

TIL https://docs.docker.com/reference/dockerfile/#copy---parents

[rcdailey]

Yep, pretty essential in the complex app example they have.