Error "platform specifier component must match" when building Docker image

[mu88]

Hi 👋🏻

I'm trying to build this Dockerfile:

FROM --platform=$TARGETARCH mu88/screenshotcreator-playwright:latest AS base
ARG TARGETARCH

FROM --platform=$BUILDPLATFORM mcr.microsoft.com/dotnet/sdk:8.0 AS build
ARG TARGETARCH
WORKDIR /src
COPY . .
RUN dotnet publish -a $TARGETARCH "/src/src/ScreenshotCreator.Api/ScreenshotCreator.Api.csproj" -o /app/publish

FROM base AS final
WORKDIR /app
COPY --from=build /app/publish .
RUN chmod +x /app/.playwright/node/*/node
ENTRYPOINT ["dotnet", "ScreenshotCreator.Api.dll"]

Here's what I try to do (following the docs):

var futureImage = new ImageFromDockerfileBuilder()
    .WithDockerfileDirectory(CommonDirectoryPath.GetSolutionDirectory(), Path.Combine("src", "ScreenshotCreator.Api"))
    .WithDockerfile("Dockerfile")
    .Build();
await futureImage.CreateAsync();

This fails with the following error:

System.InvalidOperationException : Docker image localhost/testcontainers/b0f62461-c8a3-4ec4-9bc0-dfdbbcf10e4c:latest has not been created.
   at DotNet.Testcontainers.Clients.DockerImageOperations.BuildAsync(IImageFromDockerfileConfiguration configuration, ITarArchive dockerfileArchive, CancellationToken ct)
   at DotNet.Testcontainers.Clients.TestcontainersClient.BuildAsync(IImageFromDockerfileConfiguration configuration, CancellationToken ct)
   at DotNet.Testcontainers.Images.FutureDockerImage.UnsafeCreateAsync(CancellationToken ct)
   at DotNet.Testcontainers.Images.FutureDockerImage.CreateAsync(CancellationToken ct)
   at Tests.Integration.Api.ProgramTests.CreateImageNowForOpenHab2() in C:\Users\MyUser\Documents\Development\GitHub\ScreenshotCreator\tests\Tests\Integration\Api\ProgramTests.cs:line 59
   at NUnit.Framework.Internal.TaskAwaitAdapter.GenericAdapter`1.BlockUntilCompleted()
   at NUnit.Framework.Internal.MessagePumpStrategy.NoMessagePumpStrategy.WaitForCompletion(AwaitAdapter awaiter)
   at NUnit.Framework.Internal.AsyncToSyncAdapter.Await[TResult](Func`1 invoke)
   at NUnit.Framework.Internal.AsyncToSyncAdapter.Await(Func`1 invoke)
   at NUnit.Framework.Internal.Commands.TestMethodCommand.RunTestMethod(TestExecutionContext context)
   at NUnit.Framework.Internal.Commands.TestMethodCommand.Execute(TestExecutionContext context)
   at NUnit.Framework.Internal.Commands.BeforeAndAfterTestCommand.<>c__DisplayClass1_0.<Execute>b__0()
   at NUnit.Framework.Internal.Commands.DelegatingTestCommand.RunTestMethodInThreadAbortSafeZone(TestExecutionContext context, Action action)



-----

One or more child tests had errors
  Exception doesn't have a stacktrace



info: ScreenshotCreator.Api.BackgroundScreenshotCreator[1]
      Background service disabled
[testcontainers.org 00:00:00.17] Connected to Docker:
  Host: npipe://./pipe/docker_engine
  Server Version: 24.0.7
  Kernel Version: 5.15.123.1-microsoft-standard-WSL2
  API Version: 1.43
  Operating System: Docker Desktop
  Total Memory: 7.64 GB
[testcontainers.org 00:00:00.31] Pattern ^(.+)\/\.idea added to the regex cache
[testcontainers.org 00:00:00.31] Pattern ^([\\\/]?(\.idea\b|$)) added to the regex cache
[testcontainers.org 00:00:00.31] Pattern ^([\\\/]?((.+)\/\.vs\b|$)) added to the regex cache
[testcontainers.org 00:00:00.31] Pattern ^([\\\/]?(\.vs\b|$)) added to the regex cache
[testcontainers.org 00:00:00.31] Pattern ^([\\\/]?(\.dockerignore\b|$)) added to the regex cache
[testcontainers.org 00:00:00.31] Pattern ^([\\\/]?(Dockerfile\b|$)) added to the regex cache
[testcontainers.org 00:02:22.47] failed to parse platform : "" is an invalid component of "": platform specifier component must match "^[A-Za-z0-9_-]+$": invalid argument

I already found #993, but I don't (yet) see how I have to modify my test to get rid of the error,

PS: The Docker image mu88/screenshotcreator-playwright:latest does exist on my local Docker daemon (here's the related Dockerfile).

[HofmeisterAn]

Did you set the build arg TARGETARCH? E.g.:

WithBuildArgument("TARGETARCH ", "linux-x64")

Can you try to enable the debug log messages? I guess the dotnet build fails.

ConsoleLogger.Instance.DebugLogLevelEnabled = true;

[HofmeisterAn]

Buildx is a Docker CLI plugin. While it is included together with BuildKit in Docker Desktop, AFIK, it is not available from the Docker Engine API. At least, that is my last status quo. I was a bit confused by the log message TBH, and thought maybe something has changed, but I think it is simply not supported - sorry I do not think I can help here.

[mu88]

Thx for your explanation, learning never stops 🙂

Does that mean that when calling docker build manually via Process.Start (or even simpler, run dotnet publish /t:PublishContainer via Process.Start) rather than using the Testcontainers API would do the job (in case either Buildx and/or the .NET SDK are installed)?

[HofmeisterAn]

Yes, if Buildx is available, the CLI will work. I am not very familiar with the implementation details of PublishContainer. AFAIK, it is not just a simple CLI wrapper. I am not sure if the target supports it. Usually, I use the provided CI tasks to build the image before executing the tests. However, supporting PublishContainer would be a cool enhancement, I think.

[mu88]

Yes, if Buildx is available, the CLI will work.

I can confirm that the following code successfully builds the Docker image on my laptop:

var rootDirectory = Directory.GetParent(Environment.CurrentDirectory)?.Parent?.Parent?.Parent?.Parent ?? throw new NullReferenceException();
var dockerfile = Path.Join(rootDirectory.FullName, "src", "ScreenshotCreator.Api", "Dockerfile");
var process = new Process
{
    StartInfo = new ProcessStartInfo
    {
        FileName = "docker",
        Arguments = $"build --platform linux/amd64 -f {dockerfile} -t screenshotcreator:dev {rootDirectory}",
        UseShellExecute = false,
        RedirectStandardOutput = true,
        CreateNoWindow = true
    }
};
process.Start();
while (!process.StandardOutput.EndOfStream)
{
    await TestContext.Progress.WriteLineAsync(await process.StandardOutput.ReadLineAsync());
}
await process.WaitForExitAsync();
process.ExitCode.Should().Be(0);

However, supporting PublishContainer would be a cool enhancement, I think.

Absolutely, I couldn't agree more! I migrated 99% of my personal projects from using a dedicated Dockerfile to dotnet publish and can confirm that this is a nice and elegant way.

Thank you for your help, @HofmeisterAn , I'm resolving this question.