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.