How to Automatically Configure appsettings.json for Different Environments in ASP.NET Core?

Automatically configure appsettings.json according to different environments in ASP.NET Core

In ASP.NET Core application development, it is often necessary to configure different settings for development, testing and production environments, such as database connection strings, Web API addresses, etc.

Create multiple appsettings.json files

To handle these different configurations, you can create multiple appsettings.json files, such as appsettings.Production.json, appsettings.Staging.json, and appsettings.Development.json. Each file contains specific settings for its corresponding environment.

Host.CreateDefaultBuilder and automatic configuration

In .NET Core 3.0 and above, you can leverage the Host.CreateDefaultBuilder method to automatically select and load the appropriate appsettings.json file. This method simplifies the configuration process by automatically building an IConfiguration object according to the following priority order:

1. appsettings.json
2. appsettings..json
3. App Key (for development environment)
4. Environment variables
5. Command line parameters

Set environment variables

To specify a specific environment to use in the appsettings.json file, you need to set the ASPNETCORE_ENVIRONMENT environment variable to a value that matches the desired environment, such as "Development", "Staging", or "Production".

Usage of Host.CreateDefaultBuilder

The following is how to implement Host.CreateDefaultBuilder in the startup class:

WebHost.CreateDefaultBuilder(args)
    .UseStartup<Startup>();

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    // ...
}

This code automatically injects environment-specific configuration objects into your Startup class constructor.

Set environment variables in different IDEs and startup settings

The method of setting environment variables differs depending on your IDE:

• Visual Studio: Project > Properties > Debug > Environment Variables
• Visual Studio Code: Edit .vscode/launch.json > env
• Launch Settings: properties/launchSettings.json > environmentVariables
• dotnet CLI: Use the syntax appropriate for your operating system to set environment variables

Read more

• Application startup in ASP.NET Core
• Configuration in ASP.NET Core
• Using multiple environments in ASP.NET Core

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