*Update: I no longer recommend the approach described in this post. I propose a better solution here: Asynchronous initialization in ASP.NET Core, revisited.* Sometimes you need to perform some initialization steps when your web application starts. However, putting such code in the Startup.Configure method is generally not a good idea, because: There's no current scope in the Configure method, so you can't use services registered with “scoped” lifetime (this would throw an InvalidOperationException: Cannot resolve scoped service ‘MyApp.
Middlewhat? The ASP.NET Core architecture features a system of middleware, which are pieces of code that handle requests and responses. Middleware are chained to each other to form a pipeline. Incoming requests are passed through the pipeline, where each middleware has a chance to do something with them before passing them to the next middleware. Outgoing responses are also passed through the pipeline, in reverse order. If this sounds very abstract, the following schema from the official ASP.