.NET Core for Linux with dockers - create docker image

Question

I want to create a docker image for code I have written in .NET Core (C# Visual Studio 2017), that can be run on Linux.

The steps - I create a new file, such as hello world:

using System;

namespace myApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
        }
    }
}

The docker file (for Windows), which had been tested and works:

FROM microsoft/dotnet:2.1-sdk
WORKDIR /app

# copy csproj and restore as distinct layers
COPY *.csproj ./
RUN dotnet restore

# copy and build everything else
COPY . ./
RUN dotnet publish -c Release -o out
ENTRYPOINT ["dotnet", "out/myApp.dll"]

The docker file for linux:

FROM microsoft/aspnetcore:2.0
WORKDIR /app
COPY ./publish .
ENTRYPOINT ["dotnet", "Receive.dll"]

The above does not work well.

When I run (in command prompt. Linux container):

docker build . -t myapp_linux

I got the message:

COPY failed: stat /var/lib/docker/tmp/docker-builder786597608/publish: no such file or directory

Also, tried changing to configuration to something like:

FROM microsoft/aspnetcore:2.0
WORKDIR /app

# copy csproj and restore as distinct layers
COPY *.csproj ./
RUN dotnet restore

# copy and build everything else
COPY . ./
RUN dotnet publish -c Release -o out
ENTRYPOINT ["dotnet", "Receive.dll"]

The above doesn't work either, and I got the message:

Did you mean to run dotnet SDK commands? Please install dotnet SDK from: http://go.microsoft.com/fwlink/?LinkID=798306&clcid=0x409

The windows docker image contains the dotnet sdk, so it can run dotnet restore and publish. The Linux image doesn't contain the dotnet sdk, it contains only the runtime. hence it can't run the restore and publish commands. — Aman B
So its better to run the restore and publish command on a dev/build machine and just copy the output to docker image — Aman B

Aman B Aman B · Accepted Answer · 2018-11-08T13:53:42

You should run the restore and publish command outside of docker file e.g. PowerShell first and then just copy the output to docker, in docker file.

1- First run in cmd or powershell:

dotnet restore
dotnet publish -o ./publish

2- In your docker file:

FROM microsoft/aspnetcore:2.0
WORKDIR /app
COPY ./publish .
ENTRYPOINT ["dotnet", "Receive.dll"]

3- Build docker image

4- Run docker container

.NET Core for Linux with dockers - create docker image

2 Answers