For existing ASP.NET Core MVC project on Windows build server, how to target a Docker container without disturbing earlier build pipeline stages?

Fixed it by two changes:
1) Change the DLL name in the Dockerfile to be case sensitive. The app runs inside a container whose OS is case sensitive Linux.
2) Change the port number mapping in the "docker run" commmand

Troubleshooting steps:
1. In a Visual Studio 2019 command prompt window, go to the publish directory
2. Run the web site "dotnet AspNetMvcCoreTestApp2.dll". This command is the same one run inside the Docker container.
It produces this output. Notice the port number 5000
info: Microsoft.Hosting.Lifetime[0]
Now listening on: http://localhost:5000
info: Microsoft.Hosting.Lifetime[0]
Now listening on: https://localhost:5001
info: Microsoft.Hosting.Lifetime[0]
Application started. Press Ctrl+C to shut down.
3. Open a browser and go to http://localhost:5000/ and the start page of the site is displayed
4. Change the Dockerfile to list the correct DLL name including case sensitive letters. Also verify thta the .NET core version in the Dockerfile is the same as the one in the Visual Stuido 2019 explorer.

# Build runtime imageFROM mcr.microsoft.com/dotnet/core/aspnet:3.0WORKDIR /appCOPY . .ENTRYPOINT ["dotnet", "AspNetCoreTestProject2.dll"]EXPOSE 80

5. Remove any images for the container in Docker if needed
   Run "docker image ls" and make note of the IMAGE_ID of the existing image if it exists
   Run "docker rmi IMAGE_ID" to remove the image
   
6. Build the docker image "docker build -t aspnetcoretestproject2 ."
   
7. Enter "docker image ls" and make note of the IMAGE_ID value for aspnetcoretestproject2
   

    REPOSITORY                             TAG                 IMAGE ID            CREATED             SIZE    aspnetcoretestproject2                 latest              58c92979be61        3 minutes ago       212MB    mcr.microsoft.com/dotnet/core/sdk      3.0-buster          4422e7fb740c        3 weeks ago         689MB

8. Run the docker image mapping local host port 5000 to port 80 inside the Docker container
   "docker run -d -p 5000:80 58c92979be61"
   
9. Verify the docker container is running by "docker container ls"

    CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                  NAMES    c52ab21b9c25        58c92979be61        "dotnet AspNetCoreTe…"   4 seconds ago       Up 2 seconds        0.0.0.0:5000->80/tcp   magical_leavitt    e4152fcb2233        f80194ae2e0c        "ping 8.8.8.8"           3 minutes ago       Up 3 minutes                               k8s_testpod_demo_default_dd2702f7-eeac-11e9-a181-00155dde9201_2

10. Open web browser and enter http://localhost:5000 in the URL bar. This should show the start page of the ASP.NET web site

Put the command "EXPOSE" before the command "ENTRYPOINT".Also, you forgot to add environment variables for ASP Core runtime.

Fixed Dockerfile:

# Build runtime imageFROM mcr.microsoft.com/dotnet/core/aspnet:3.0WORKDIR /appEXPOSE 80 # container listens on the port at runtimeENV ASPNETCORE_URLS=http://+:80 # bind port 80 for httpCOPY . .ENTRYPOINT ["dotnet", "AspNetCoreTestProject2.dll"]

Read more about the ASPNETCORE_URLS here