--- title: Application Startup in ASP.NET Core author: ardalis description: Explains the Startup class in ASP.NET Core. keywords: ASP.NET Core, Startup, Configure method, ConfigureServices method ms.author: tdykstra manager: wpickett ms.date: 02/29/2017 ms.topic: article ms.assetid: 6538df00-4ec2-45e4-811a-d7ce2ee608ed ms.technology: aspnet ms.prod: asp.net-core uid: fundamentals/startup --- # Application Startup in ASP.NET Core By [Steve Smith](http://ardalis.com) and [Tom Dykstra](https://github.com/tdykstra/) The `Startup` class configures the request pipeline that handles all requests made to the application. ## The Startup class ASP.NET Core apps require a `Startup` class. By convention, the `Startup` class is named "Startup". You specify the startup class name in the `Main` programs [WebHostBuilderExtensions](https://docs.microsoft.com/aspnet/core/api/microsoft.aspnetcore.hosting.webhostbuilderextensions) [`UseStartup`](https://docs.microsoft.com/aspnet/core/api/microsoft.aspnetcore.hosting.webhostbuilderextensions#Microsoft_AspNetCore_Hosting_WebHostBuilderExtensions_UseStartup__1_Microsoft_AspNetCore_Hosting_IWebHostBuilder_) method. You can define separate `Startup` classes for different environments, and the appropriate one will be selected at runtime. If you specify `startupAssembly` in the WebHost configuration or options, hosting will load that startup assembly and search for a `Startup` or `Startup[Environment]` type. See [FindStartupType](https://github.com/aspnet/Hosting/blob/rel/1.1.0/src/Microsoft.AspNetCore.Hosting/Internal/StartupLoader.cs) in `StartupLoader` and [Working with multiple environments](environments.md#startup-conventions). `UseStartup` is the recommended approach. The `Startup` class constructor can accept dependencies that are provided through [dependency injection](dependency-injection.md). You can use `IHostingEnvironment` to set up [configuration](configuration.md) sources and `ILoggerFactory` to set up [logging](logging.md) providers. The `Startup` class must include a `Configure` method and can optionally include a `ConfigureServices` method, both of which are called when the application starts. The class can also include [environment-specific versions of these methods](environments.md#startup-conventions). Learn about [handling exceptions during application startup](error-handling.md#startup-exception-handling). ## The Configure method The `Configure` method is used to specify how the ASP.NET application will respond to HTTP requests. The request pipeline is configured by adding [middleware](middleware.md) components to an `IApplicationBuilder` instance that is provided by dependency injection. In the following example from the default web site template, several extension methods are used to configure the pipeline with support for [BrowserLink](http://vswebessentials.com/features/browserlink), error pages, static files, ASP.NET MVC, and Identity. [!code-csharp[Main](../common/samples/WebApplication1/Startup.cs?highlight=8,9,10,14,17,19,21&start=58&end=84)] Each `Use` extension method adds a [middleware](middleware.md) component to the request pipeline. For instance, the `UseMvc` extension method adds the [routing](routing.md) middleware to the request pipeline and configures [MVC](../mvc/index.md) as the default handler. For more information about how to use `IApplicationBuilder`, see [Middleware](middleware.md). Additional services, like `IHostingEnvironment` and `ILoggerFactory` may also be specified in the method signature, in which case these services will be [injected](dependency-injection.md) if they are available. ## The ConfigureServices method The [ConfigureServices](https://docs.microsoft.com/en-us/aspnet/core/api/microsoft.aspnetcore.hosting.startupbase#Microsoft_AspNetCore_Hosting_StartupBase_ConfigureServices_Microsoft_Extensions_DependencyInjection_IServiceCollection_) method is optional; but if used, it's called before the `Configure` method by the runtime (some features are added before they're wired up to the request pipeline). [Configuration options](configuration.md) are set in this method. For features that require substantial setup there are `Add[Service]` extension methods on [IServiceCollection](https://docs.microsoft.com/en-us/aspnet/core/api/microsoft.extensions.dependencyinjection.iservicecollection). This example from the default web site template configures the app to use services for Entity Framework, Identity, and MVC: [!code-csharp[Main](../common/samples/WebApplication1/Startup.cs?highlight=4,7,11&start=40&end=55)] Adding services to the services container makes them available within your application via [dependency injection](dependency-injection.md). ## Services Available in Startup ASP.NET Core dependency injection provides application services during an application's startup. You can request these services by including the appropriate interface as a parameter on your `Startup` class's constructor or one of its `Configure` or `ConfigureServices` methods. Looking at each method in the `Startup` class in the order in which they are called, the following services may be requested as parameters: * In the constructor: `IHostingEnvironment`, `ILoggerFactory` * In the `ConfigureServices` method: `IServiceCollection` * In the `Configure` method: `IApplicationBuilder`, `IHostingEnvironment`, `ILoggerFactory`, `IApplicationLifetime` ## Additional Resources * [Working with Multiple Environments](environments.md) * [Middleware](middleware.md) * [Logging](logging.md) * [Configuration](configuration.md)