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What is the problem when reciving MSB1001: Unkown switch, when trying to publishing C# application?

I am trying to dockerize my web API with docker and I have encountered an error MSB1001: Unkown switch. More details can be found in the cmd prompt image
Does anyone know what this means, I've tried to follow up on this in GitHub discussions and posts in StackOverflow.
My Dockerfile:
FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
WORKDIR C:\Users\Alexa\OneDrive\Desktop\SortIT\Api
# Copy everything
COPY . .
# Restore as distinct layers
RUN dotnet restore "./Api.csproj"
RUN dotnet publish "/Api.csproj" -c release -o ./
# Build runtime image
FROM mcr.microsoft.com/dotnet/aspnet:6.0
COPY --from=build /Api .
ENTRYPOINT ["dotnet", "Api.dll"]
My file directory

There are a number of issues with your Dockerfile. The one giving you the 'unknown switch' is on the publish statement, where you've given the project file name as /Api.csproj. It should be ./Api.csproj.
As others have pointed out, your WORKDIR uses Windows syntax, but you're building a Linux image and should use Linux syntax. I like to use /src as the directory in my build steps.
You publish the project to ./ which means that you'll end up with a directory that contains both your source and the published project. You want to keep them separate, so you can copy only the published project into the final image.
Which those changes, you end up with
FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
WORKDIR /src
# Copy everything
COPY . .
# Restore as distinct layers
RUN dotnet restore "./Api.csproj"
RUN dotnet publish "./Api.csproj" -c Release -o out
# Build runtime image
FROM mcr.microsoft.com/dotnet/aspnet:6.0
COPY --from=build /src/out .
ENTRYPOINT ["dotnet", "Api.dll"]

I assume you have build context in the folder with Api.csproj file. First - WORKDIR sets the current working directory in the container. It is not a directory on the host system. You start with a directory where you copy source code from the build context to the container. Good name for it /src
FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
WORKDIR /src # current directory in the container
COPY . . # Copy everything from build context to /src
RUN dotnet restore "Api.csproj"
Note that in order to optimize the build process and use caching, its better to start with copying *.csproj file only and restore dependencies. Because source code changes more often then dependencies of the application.
Next you want to build/publish your application somewhere in a container. Usually you create new directory for that and don't use the system root:
#publish app to folder /publish
RUN dotnet publish "Api.csproj" -c release -o /publish
And the last step - you should copy the published application to the runtime container. Here you set the current directory to the directory where the published application will be located:
FROM mcr.microsoft.com/dotnet/aspnet:6.0
WORKDIR /app #now set the current directory to /app
COPY --from=build /publish . #copy from build stage to /app
And don't forget to expose ports used by your API.
Dockerfile:
FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
WORKDIR /src
COPY "Api.csproj" .
RUN dotnet restore "Api.csproj"
COPY . .
RUN dotnet publish "Api.csproj" -c release -o /publish
FROM mcr.microsoft.com/dotnet/aspnet:6.0
WORKDIR /app
EXPOSE 80
COPY --from=build /publish .
ENTRYPOINT ["dotnet", "Api.dll"]

Docker multistage build error c# (v20.10.8)

I have a microservice project and it includes docker. I am using .Net and .Net Framework. .Net 5.0 and .Net Framework 4.7.2
I don't get an error while building the project, but when I need to upload it to docker, I get an error. What is the solution ?
WORKDIR /app
EXPOSE 80
FROM mcr.microsoft.com/dotnet/sdk:5.0 AS build
WORKDIR /src
COPY ["Services/Customers/Wise.Customers/Wise.Customers.csproj",
"Services/Customers/Wise.Customers/"]
COPY ["Services/Customers/Wise.Customers.Application/Wise.Customers.Application.csproj",
"Services/Customers/Wise.Customers.Application/"]
COPY ["Services/Customers/Wise.Customers.Domain/Wise.Customers.Domain.csproj",
"Services/Customers/Wise.Customers.Domain/"]
COPY ["Services/Wise.Core/Wise.Core.csproj", "Services/Wise.Core/"]
COPY ["Services/Customers/Wise.Customers.Infrastructure/Wise.Customers.Infrastructure.csproj",
"Services/Customers/Wise.Customers.Infrastructure/"]
RUN dotnet restore "Services/Customers/Wise.Customers/Wise.Customers.csproj"
COPY . .
WORKDIR "/src/Services/Customers/Wise.Customers"
RUN dotnet build "Wise.Customers.csproj" -c Release -o /app/build
FROM build AS publish
RUN dotnet publish "Wise.Customers.csproj" -c Release -o /app/publish
FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "Wise.Customers.dll"]
error;

how to include class library reference into docker file

i'm trying to build docker file for .net core application which is having reference of class library whenever i'm trying to build docker i'm getting below error.
Skipping project because it was not found
below is the docker file which i'm using
FROM mcr.microsoft.com/dotnet/core/sdk:3.1 AS build-env
WORKDIR /app
# Copy csproj and restore as distinct layers
COPY *.csproj ./
RUN dotnet restore
# Copy everything else and build
COPY . ./
RUN dotnet publish -c Release -o out
# Build runtime image
FROM mcr.microsoft.com/dotnet/core/aspnet:3.1
WORKDIR /app
COPY --from=build-env /app/out .
ENTRYPOINT ["dotnet", "testapp.dll"]

You need to move the Dockerfile to the solution level, and reference the projects using [Folder]/[Project].csproj.
Here is my Dockerfile (located in the solution level):
FROM mcr.microsoft.com/dotnet/aspnet:3.1 AS base
WORKDIR /app
EXPOSE 80
EXPOSE 443
FROM mcr.microsoft.com/dotnet/sdk:3.1 AS build
WORKDIR /src
COPY ["SumApi/SumApi.csproj", "SumApi/"]
COPY ["Shared/Shared.csproj", "Shared/"]
RUN dotnet restore "SumApi/SumApi.csproj"
COPY . .
WORKDIR "/src/SumApi"
RUN dotnet build "SumApi.csproj" -c Release -o /app/build
FROM build AS publish
RUN dotnet publish "SumApi.csproj" -c Release -o /app/publish
FROM base AS final
WORKDIR /app`enter code here`
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "SumApi.dll"]
Learned it from here: https://imranarshad.com/dockerize-net-core-web-app-with-dependent-class-library/

multiple asp.net core project have problems in docker

I used Visual Studio 2019 and created my dockerfile with it.
my docker file
#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/aspnet:3.1-buster-slim AS base
WORKDIR /app
EXPOSE 80
EXPOSE 443
FROM mcr.microsoft.com/dotnet/core/sdk:3.1-buster AS build
WORKDIR /src
COPY ["BackEnd.service.api.csproj", "BackEnd.service.api"]
COPY ["src/BackEnd.Service.Application/BackEnd.Service.Application.csproj", "src/BackEnd.Service.Application/"]
COPY ["src/BackEnd.Service.Model/BackEnd.Service.Model.csproj", "src/BackEnd.Service.Model/"]
RUN dotnet restore "src/BackEnd.service.api/BackEnd.service.api.csproj"
COPY . .
WORKDIR "/src/src/BackEnd.service.api"
RUN dotnet build "BackEnd.service.api.csproj" -c Release -o /app/build
FROM build AS publish
RUN dotnet publish "BackEnd.service.api.csproj" -c Release -o /app/publish
FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "BackEnd.service.api.dll"]
and my project tree:
now I have this error:
please help me to how can I change my route of project to build it in docker?

The problem is most likely your build context. Visual Studio seems to be using you web app project as the build context, meaning it can't access your Application and Model projects from the src folder.
I can suggest that you try to explicitly set the Dockerfile context in your web app's .csproj file with the following property to the src directory from which all projects are accessible:
<PropertyGroup>
<TargetFramework>netcoreapp3.1</TargetFramework>
<DockerfileContext>..\</DockerfileContext>
</PropertyGroup>
Then you may need to update your Dockerfile to point to your reference projects (Application and Model) to be relative towards the src folder.
COPY ["BackEnd.service.api/BackEnd.service.api.csproj", "src/BackEnd.service.api"]
COPY ["BackEnd.Service.Application/BackEnd.Service.Application.csproj", "src/BackEnd.Service.Application/"]
COPY ["BackEnd.Service.Model/BackEnd.Service.Model.csproj", "src/BackEnd.Service.Model/"]
RUN dotnet restore "src/BackEnd.service.api/BackEnd.service.api.csproj"
You may need to play around with the directories a bit, but its very important to remember that the build context is the key.
Alternatively you can try to add a docker-compose project to your solution and have that build your Dockerfile. You will be able to specify a build context in the docker-compose.yml file for each project that should be built.

I suggest follow this article aspnetcore-app-dockerfiles to make dockerfile manually instead of vs project's docker template. Also, use .dockerignore will help you simplify your dockerfile script, ignore files might not need runtime.
Here is an example from my project, hope helps.
FROM mcr.microsoft.com/dotnet/core/aspnet:3.1-bionic AS base
WORKDIR /app
EXPOSE 80
EXPOSE 443
FROM mcr.microsoft.com/dotnet/core/sdk:3.1-bionic AS build
WORKDIR /build
COPY . .
RUN dotnet restore
RUN dotnet publish "src/BackEnd.service.api/BackEnd.service.api.csproj" -c Release -o /app --no-restore
FROM base AS final
WORKDIR /app
COPY --from=build /app .
ENTRYPOINT ["dotnet", "BackEnd.service.api.dll"]

How to build one docker image for multiple projects?

In my project I am using .net core 2.2 , recently I am using additional class library inside my project.
When I am trying to build my image it can not found my dll.
My docker file looks like:
FROM mcr.microsoft.com/dotnet/core/sdk:2.2 AS build-env
WORKDIR /app
# Copy csproj and restore as distinct layers
COPY *.csproj ./
RUN dotnet restore
COPY . ./
RUN dotnet publish -c Release -o out
# Build runtime image
FROM mcr.microsoft.com/dotnet/core/aspnet:2.2
WORKDIR /app
EXPOSE 80
COPY --from=build-env /app/out .
ENTRYPOINT ["dotnet", "LibvirtManagement.dll"]
I am getting error like this:
The project file "/JenkinsService/JenkinsService.csproj" was not found.
[/app/LibvirtManagement.sln]
The command '/bin/sh -c dotnet publish -c Release -o out' returned a non-zero code: 1

The error message is pretty straightforward, you're missing JenkinsService.csproj and other files from this project in docker container where you build it. You need to copy these files as well.
If you're using Visual Studio the easiest way to do it is to right-click executable project file (LibvirtManagement in your case) and then select Add -> Docker Support.... It will auto-generate correct Dockerfile for you
EDIT: this is what this tool created for me:
#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/aspnet:2.2-stretch-slim AS base
WORKDIR /app
EXPOSE 80
EXPOSE 443
FROM mcr.microsoft.com/dotnet/core/sdk:2.2-stretch AS build
WORKDIR /src
COPY ["LibvirtManagement/LibvirtManagement.csproj", "LibvirtManagement/"]
COPY ["JenkinsService/JenkinsService.csproj", "JenkinsService/"]
RUN dotnet restore "LibvirtManagement/LibvirtManagement.csproj"
COPY . .
WORKDIR "/src/LibvirtManagement"
RUN dotnet build "LibvirtManagement.csproj" -c Release -o /app/build
FROM build AS publish
RUN dotnet publish "LibvirtManagement.csproj" -c Release -o /app/publish
FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "LibvirtManagement.dll"]