A .NET generic host is an object that encapsulates an app’s resources and lifetime functionality like dependency injection, logging and configuration.

One example when a generic host is useful is when you want to create a worker which fetches jobs from some kind of message queue.

The code below creates an IHost instance configured with some defaults and an implementation of a IHostedService

await Host.CreateDefaultBuilder(args)
    .ConfigureServices(services =>

The CreateDefaultBuilder creates an IHostBuilder object which comes with some default configuration set.

  • The content root is set to the result of Directory.GetCurrentDirectory()
  • It loads host configuration from command-line and environment variables prefixed with DOTNET_
  • App configuration is loaded from:
    • appsettings.json
    • appsettings.{Environment}.json
    • User secrets
    • Environment variables
    • Command-line arguments
  • Some default logging providers are activated

So what is the difference between HostConfiguration and AppConfiguration

Host configuration is used for configuring the properties of the IHostEnvironment implementation. This interface has properties like:

  • EnvironmentName - (Development/Production)
  • ContentRootPath - The base path for the executable hosting the app and content files like configuration files. The base path is the default for the JsonConfigurationProvider which is used when build the AppConfiguration.

Host configuration is available inside ConfigureAppConfiguration on the HostBuilderContext.Configuration object. When AppConfiguration is built the HostBuilderContext.Configuration is replaced with the app configuration

Host configuration can be configured with ConfigureHostConfiguration. Environment variables with the prefix DOTNET_ will be loaded into host configuration by default.

App configuration is configured by calling ConfigureAppConfiguration on IHostBuilder and is then available HostBuilderContext.Configuration and can be accessed with requiring IConfiguration interface with the help of dependency injection.


The host configuration is used to configure the generic host but also as a way to control the outcome of ConfigureAppConfiguration. I guess the reason to split these up in two steps is to be able to configure more how the application configuration should look like depending on the hosting environment. One example could be if you want to load some other JsonConfiguration sources for development or production.