# Custom Endpoint Initialization


Classes that implement `NServiceBus.INeedInitialization` are created and called as one of the first steps performed during endpoint creation. Use `INeedInitialization` to register custom endpoint configuration logic.

Instances are:

 - Located by [assembly scanning](/nservicebus/hosting/assembly-scanning.md).
 - Created as one of the first steps when the bus is created.
 - Created on the same thread that is creating the bus.
 - Created with [`Activator.CreateInstance(...)`](https://learn.microsoft.com/en-us/dotnet/api/system.activator.createinstance) which means they:
    - Are not resolved from [dependency injection](/nservicebus/dependency-injection/index.md) (even if they are registered there).
    - Will not have any dependencies injected.
    - Must have a default constructor.

Once instantiated, `Customize(...)` is called on each instance. These calls are made on the same thread that is creating the endpoint. The order in which instances are instantiated and run is non-deterministic and should not be relied upon.

Exceptions thrown by instances of `INeedInitialization` are not handled by NServiceBus and will bubble up to the caller, creating the endpoint.

> [!NOTE]
> Instances of `INeedInitialization` are created after type-scanning has occurred. Do not attempt to alter the types to be scanned from an instance of `INeedInitialization`.

<!-- snippet: lifecycle-ineedinitialization -->

```cs
class NeedsInitialization :
    INeedInitialization
{
    public void Customize(EndpointConfiguration endpointConfiguration)
    {
        // Perform initialization
        // This is after Type Scanning.
        // Do NOT call the following here:
        // endpointConfiguration.AssemblyScanner();
    }
}
```

<!-- endsnippet -->