The engine, a class which implements the interface IEngine, is the central object that is responsible for managing server-side state (among its many other responsibilities). The engine is itself stored as an HttpSession attribute.

Because the internal state of the engine can change, the framework will re-store the engine into the HttpSession at the end of most requests. This ensures that any changes to the Visit object are properly replicated.

The simplest way to replicate server-side state is simply not to have any. With some care, Tapestry applications can run stateless, at least until some actual server-side state is necessary.