What is the intention of AZURE_FUNCTIONS_ENVIRONMENT variable?

[sandeepiiit]

Is your question related to a specific version? If so, please specify:

Function runtime v2

What language does your question apply to? (e.g. C#, JavaScript, Java, All)

C#

Question

When running a C# function in Visual Studio, I notice that an environment variable called "AZURE_FUNCTIONS_ENVIRONMENT" is set to Development? How is this variable used? Is AZURE_FUNCTIONS_ENVIRONMENT to functions what ASPNETCORE_ENVIRONMENT is for asp dotnet core web apps?
I am planning to use on those two variables to load an environment specific settings file: appsettings.{environmentname}.json, and I am wondering which one is the right approach?

[kashimiz]

You'll want to use AZURE_FUNCTIONS_ENVIRONMENT. The Functions runtime that powers a Function app on Azure is the WebHost project in this repo. As the host is initializing, it looks for the AZURE_FUNCTIONS_ENVIRONMENT app setting (as EnvironmentSettingNames.EnvironmentNameKey) and passes it to the IWebHostBuilder. Using only ASPNETCORE_ENVIRONMENT can lead to desired behavior changes and telemetry being missed.