If you are debugging with VS2017/9 and want to pass environment variables to your container then read this post, if you are looking for picture of cats then sorry but leave a comment how you got here
Create a new text file, the name doesn’t matter, but i called mine Dockerfile.env
Add this file to your .csproj file.
Not really a step but you you can simply query your Environment variable in the usual fashion (Environment.GetEnvironmentVariable())
Needless to say when you run in production you’ll need to pass the Environment variable according to Docker documentation which I don’t cover here