The appsettings.json file has this setting:
{
"App": {
"Environment": "DEV"
}
}
You access that in code using the key App:Environment. You can use that as the name of an environment variable too, but not all platforms like having a colon in the name so you can also use App__Environment.
You’ll see that in the Dockerfile, and this is how you override the setting in the image for one container:
docker run -d -p 8084:80 -e App__Environment=PROD simple-web
You need to use a different port, because only one container can listen on each port
Browse to http://localhost:8084/ and you’ll see the updated value.