Visual Studio: docker build fails when linked files are in the project

Question

I have a .NET 6 Console project that includes 2 binaries as linked files:

 <ItemGroup>
    <None Include="..\HFMath\bin\HFMath.dll" Link="HFMath.dll">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>
    <None Include="..\HFMath\bin\libHFMath.so" Link="libHFMath.so">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>
  </ItemGroup>

I need to deploy it as a docker container. The Dockerfile scaffolded by Visual Studio is

FROM mcr.microsoft.com/dotnet/runtime:6.0 AS base
WORKDIR /app

FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
WORKDIR /src
COPY ["ConsoleApp1/ConsoleApp1.csproj", "ConsoleApp1/"]
RUN dotnet restore "ConsoleApp1/ConsoleApp1.csproj"
COPY . .
WORKDIR "/src/ConsoleApp1"
RUN dotnet build "ConsoleApp1.csproj" -c Release -o /app/build

FROM build AS publish
RUN dotnet publish "ConsoleApp1.csproj" -c Release -o /app/publish

FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "ConsoleApp1.dll"]

when I run docker build, I get the following error:

#15 1.054   Determining projects to restore...
#15 1.322   All projects are up-to-date for restore.
#15 2.552 /usr/share/dotnet/sdk/6.0.100/Microsoft.Common.CurrentVersion.targets(5100,5): error MSB3030: Could not copy the file "/src/HFMath/bin/libHFMath.so" because it was not found. [/src/ConsoleApp1/ConsoleApp1.csproj]
#15 2.552 /usr/share/dotnet/sdk/6.0.100/Microsoft.Common.CurrentVersion.targets(5100,5): error MSB3030: Could not copy the file "/src/HFMath/bin/HFMath.dll" because it was not found. [/src/ConsoleApp1/ConsoleApp1.csproj]
#15 2.556
#15 2.556 Build FAILED.

I know that docker doesn't support symlinks, but I still need to build the image. How do I fix this (without changing the .NET project)?

Are the files being copied into the container and at the path specified in the error? The error messages seems to indicate they aren't. — Simply Ged, Nov 22 '21 at 03:47
@SimplyGed the dockerfile is scaffolded by Visual Studio. not manually created. It should take care of what is needed — Franco Tiveron, Nov 22 '21 at 21:33
Is the HFMath.dll stored under the `src` folder for your project e.g. `src\HFMath\bin\HFMath.dll? Based on the `.csproj` file and the error from Docker it looks like it is outside of `src`? Docker is copying files from the `src` folder for the build `COPY . .` so if the file is not inside the `src` folder it will not be copied. Even though VS created the Dockerfile, does not guarantee that it copies all the files, especially if they are outside of the `build context`. https://stackoverflow.com/questions/27068596/how-to-include-files-outside-of-dockers-build-context HTH — Simply Ged, Nov 23 '21 at 02:58
@SimplyGed Please note that the question is not "why it doesn't work", but "how do I fix it". Would you be able to show a Dockerfile I can use to fix this issue, without touching the project? — Franco Tiveron, Nov 23 '21 at 04:21

score 1 · Answer 1 · answered Nov 23 '21 at 06:57

Problem

If you have auto generated the Dockerfile using Visual Studio, it will also have created a .dockerignore file (usually in the .sln folder). That file will contain an entry to exclude **/bin from the build context.

This means when the COPY . . executes, it is ignoring the files in any bin folder

Solution

Find and edit the .dockerignore file.
Add the line !HFMath/bin/ - this will tell Docker to NOT ignore the HFMath/bin folder
Run your docker build command again

Visual Studio: docker build fails when linked files are in the project

1 Answers1