Small image testing building and running dotnet core 3.0
$ git clone https://github.com/slamidtfyn/docker-dotnet3.git
$ cd docker-dotnet3
$ docker build -t dotnet3 .
$ docker run dotnet3
Hello World!
https://hub.docker.com/r/slamidtfyn/dotnet3
$ docker run slamidtfyn/dotnet3
Hello World!