Unable to start .NET Core 3.1 Worker Service on Docker using Serilog

Question

I'm writing a .Net Core 3.1 Worker Service application using Visual Studio 2019 (Docker support enabled).

If I start the app using Docker all works well but when I add Serilog.AspNetCore 3.4.0 dependency to the project I'm not able to debug with docker anymore.

Cases:

• Start app locally without Serilog --> OK
• Start app on Docker without Serilog --> OK
• Start app locally with Serilog --> OK
• Start app on Docker with Serilog --> ERROR

The Visual Studio returned error is:

and this is the console returned error:

-------------------------------------------------------------------
You may only use the Microsoft .NET Core Debugger (vsdbg) with
Visual Studio Code, Visual Studio or Visual Studio for Mac software
to help you develop and test your applications.
-------------------------------------------------------------------
It was not possible to find any compatible framework version
The framework 'Microsoft.AspNetCore.App', version '3.1.0' was not found.
  - No frameworks were found.

You can resolve the problem by installing the specified framework and/or SDK.

The specified framework can be found at:
  - https://aka.ms/dotnet-core-applaunch?framework=Microsoft.AspNetCore.App&framework_version=3.1.0&arch=x64&rid=debian.10-x64
The program 'dotnet' has exited with code 150 (0x96).

EDIT:

This is VS 2019 automatically generated Dockerfile:

#See https://aka.ms/containerfastmode to understand how Visual Studio uses this Dockerfile to build your images for faster debugging.

FROM mcr.microsoft.com/dotnet/core/runtime:3.1-buster-slim AS base
WORKDIR /app

FROM mcr.microsoft.com/dotnet/core/sdk:3.1-buster AS build
WORKDIR /src
COPY ["MensaNotificationService/MensaNotificationService.csproj", "MensaNotificationService/"]
RUN dotnet restore "MensaNotificationService/MensaNotificationService.csproj"
COPY . .
WORKDIR "/src/MensaNotificationService"
RUN dotnet build "MensaNotificationService.csproj" -c Release -o /app/build

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

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

What is the problem and how I can solve it?

Answer 1

The error is clear - the ASP.NET Core runtime is missing. This isn't even a Visual Studio bug, as the Worker Service template is meant to create a background process, not a web app. The .NET Runtime alone doesn't include the ASP.NET Core runtime.

If you want to use Serilog with Microsoft.Extensions.Logging in a worker service, use Serilog.Extensions.Hosting or Serilog.Extensions.Logging package, not Serilog.AspNetcore. The AspNetCore package adds ASP.NET Core-specific extensions to Serilog.Extensions.Hosting.

If you really want to host a web app with a long running service as a daemon, you need to change the runtime to `aspnet. This is shown in Dockerize an ASP.NET Core application as well. The example docker file uses :

# Build runtime image
FROM mcr.microsoft.com/dotnet/core/aspnet:3.1
WORKDIR /app
COPY --from=build-env /app/out .
ENTRYPOINT ["dotnet", "aspnetapp.dll"]

A better solution though, would be to use one of the ASP.NET Core templates and add a BackgroundService to it.