How Does ASP.NET Core Automatically Load Configuration Settings Based on Different Build Environments?

Environment configuration in ASP.NET Core application is automatically loaded

ASP.NET Core apps use appsettings.json files to store configuration settings, including database connection strings, API URLs, etc. However, these settings often vary depending on the development environment (local, test, production). To solve this problem, ASP.NET Core provides a flexible mechanism to load different appsettings files based on the build configuration.

Multiple Appsettings files

The

solution involves creating multiple appsettings files, such as appsettings.Production.json and appsettings.Development.json. Each file contains configuration settings specific to the corresponding environment.

Auto loading

To automatically load the corresponding appsettings file, you can use ASP.NET Core's Host.CreateDefaultBuilder method. This method initializes the configuration object based on the following sources, in the following order:

• appsettings.json
• appsettings.{Environment}.json (e.g. appsettings.Development.json)
• App Key (in development environment)
• Environment variables
• Command line parameters

By setting the ASPNETCORE_ENVIRONMENT environment variable to the desired environment (for example, "Production" or "Development"), the configuration system will automatically load the corresponding appsettings.{Environment}.json file.

Environment variable settings

Environment variables can be set in the following ways:

• Visual Studio: Project > Properties > Debug > Environment Variables
• Visual Studio Code: Edit .vscode/launch.json > env
• Launch settings: properties/launchSettings.json > environmentVariables
• .NET CLI: Use the syntax for setting environment variables that is appropriate for your operating system

Code Example

Here is an example of using Host.CreateDefaultBuilder:

<code class="language-csharp">WebHost.CreateDefaultBuilder(args)
    .UseStartup<Startup>()
    .Build();</code>

In the Startup class, the configuration object is automatically injected:

<code class="language-csharp">public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }
    public IConfiguration Configuration { get; }
}</code>

With this mechanism, ASP.NET Core applications can easily load different configuration settings depending on the build environment, ensuring that the appropriate values ​​are used during execution.

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