Explain the principle of operation of a service that uses state, and how it differs from a stateless approach.

A service that uses stateful storage keeps information about previous interactions with the client or internal data between requests. This allows the service to consider the context and change behavior depending on the history.

Unlike a stateless service, which does not store state between requests and processes each request independently, a stateful service requires state management, which complicates scaling and fault tolerance.

For example, a stateful service can store a user's session or the progress of a task, while in a stateless service, each request is processed as new, without considering previous data.