A service lifetime is the dependency-injection rule that controls when a service instance is created and how long it is retained. ASP.NET Core services support shared application functionality such as logging and database access; registration in Program.cs determines how dependencies are resolved. section 14.0
Choose the registration according to the required instance boundary:
- Transient: AddTransient creates a new implementation instance for every dependency resolution. A GuidService with a private Guid makes repeated resolutions visibly different. section 14.4.1
- Scoped: AddScoped provides the usual one-service-object-per-HTTP-request behavior. Resolve it through HttpContext.RequestServices so the service belongs to the current request scope. section 14.4.3
- Dependencies can use different lifetimes, but a dependency resolved through a scoped service can behave as though it has the scoped lifetime. section 14.5.1
Observe the lifetime
Register `builder.Services.AddTransient<IResponseFormatter, GuidService>()`, inject `IResponseFormatter` into the `endpoint/function` handler, and request `/endpoint/function`. Different GUID values demonstrate transient resolution. Change the registration to `AddScoped`; resolutions within one HTTP request then use the scoped service object.
When configuring the request pipeline in Program.cs, create a scope before obtaining a scoped service; requesting one without a scope raises an exception. Dependency chains are resolved by inspecting constructors and recursively creating required services. section 14.4.3 section 14.5.1
