To configure and manage multiple environments in ASP.NET Core, you use a combination of environment variables and structured configuration files. At a high level, you create separate appsettings.{EnvironmentName}.json files and set the ASPNETCORE_ENVIRONMENT variable to tell the application which file to use.

Step 1: Create Environment-Specific Configuration Files

By default, an ASP.NET Core project includes appsettings.json and appsettings.Development.json. You can create additional files for other environments, such as staging or production. Settings in environment-specific files override the base appsettings.json file.

Example File Structure:

• appsettings.json (base settings for all environments)
• appsettings.Development.json (overrides for the Development environment)
• appsettings.Staging.json (overrides for the Staging environment)
• appsettings.Production.json (overrides for the Production environment)

Example appsettings.Development.json:

{
  "Logging": {
    "LogLevel": {
      "Default": "Debug",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "ConnectionStrings": {
    "DefaultConnection": "Server=(localdb)\\mssqllocaldb;Database=DevelopmentDb;..."
  }
}

Step 2: Set the ASPNETCORE_ENVIRONMENT Variable

ASP.NET Core applications read the ASPNETCORE_ENVIRONMENT variable at startup to determine the current environment.

To set the variable:

• In Visual Studio: Modify the launchSettings.json file inside the Properties folder. This is used only for local development and overrides any system-level environment variables.

"profiles": {
  "MyProject": {
    "commandName": "Project",
    "environmentVariables": {
      "ASPNETCORE_ENVIRONMENT": "Development"
    }
  },
  "StagingProfile": {
    "commandName": "Project",
    "environmentVariables": {
      "ASPNETCORE_ENVIRONMENT": "Staging"
    }
  }
}

• On the server: Set the ASPNETCORE_ENVIRONMENT variable in your hosting environment (IIS, Azure, Docker).
• IIS: Configure it in the web.config file or in IIS Manager for the app pool.
• Docker: Set it in your Dockerfile or docker-compose.yml.
• Azure App Service: Add a new Application Setting named ASPNETCORE_ENVIRONMENT in the Azure portal.

Step 3: Access Configuration in Your Code

ASP.NET Core's built-in dependency injection provides the IConfiguration and IHostEnvironment services to access configuration settings and determine the current environment at runtime.

Using IConfiguration to Retrieve Settings:

// In a controller or service, inject IConfiguration
public class MyService(IConfiguration configuration)
{
    private readonly string _connectionString = configuration.GetConnectionString("DefaultConnection");

    public void DoSomething()
    {
        // Use the connection string dynamically based on the current environment
    }
}

Using IHostEnvironment for Environment-Specific Logic:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage(); // Show detailed errors in development
    }
    else
    {
        app.UseExceptionHandler("/Error"); // Generic error page in production
    }

    if (env.IsEnvironment("Staging"))
    {
        // Add staging-specific middleware
    }
}

Advanced Environment Management

• Environment-specific service registration: Conditionally register services using if (env.IsDevelopment()) inside ConfigureServices.
• Centralized configuration: Use Azure App Configuration or HashiCorp Vault to manage and retrieve settings dynamically for multiple applications.
• Configuration key hierarchy: Environment variables take precedence over JSON settings, and environment-specific JSON overrides the base appsettings.json.