Hi Kazys! Good to hear from you.

In an ASP.NET Core application, the runtime selects the environment (Development, Staging, Production, etc.) based on the ASPNETCORE_ENVIRONMENT environment variable. Here's how it works:

Environment Variable Setting:

Each profile in launchSettings.json sets the ASPNETCORE_ENVIRONMENT variable (e.g., "Development").

Runtime Selection: When the application starts, the runtime reads ASPNETCORE_ENVIRONMENT to determine which environment-specific configuration to load, such as appsettings.Development.json.

Switching Profiles: Locally: In Visual Studio, switch profiles using the dropdown to set the environment variable. Its located near the start button where you can select IIS Express or your project name.

Deployment: On servers or in cloud environments, set the ASPNETCORE_ENVIRONMENT variable to control the environment. This setup ensures the application loads the correct configuration and services based on the environment it's running in.

Ujjwal Singh now it is more clear, thank you!