aspnet core 2.2 web app environment variables not changing in docker

I've got an ASP.NET core 2.2 web app that I have enabled docker support for. I have created a test app here for review here.

I am running it in VS with Docker locally. I want to add environment variables/secrets to the app settings secrets in order to override the values in the appsettings.json file. In order to do this locally, I have tried changing values in:

• launchsettings.json
• Dockerfile

however, for both of these, when I attach to my docker instance and printenv the variable values, I find that the variable for ASPNETCORE_ENVIRONMENT still shows up as Development.

I am attaching to the running container like this:

docker exec -t -i 4c05 /bin/bash

I have searched all files in my solution. I can't find ASPNETCORE_ENVIRONMENT being set to Development anywhere in the solution. However, somehow, the environment variable is still being set with that value.

What could be going wrong? I want that variable to change. Once working, what I really want to do is to add a connection string secret to environment variables so that it can be used locally via the appsettings.json file or via a docker secret environment variable if the aspnetcore web app is running in a container. I think I've got this code working, it's just that the variables are not being deployed as expected to the running container.

My VS version is:

thanks