What is the difference between a stateless and stateful service?
A stateless service instance can handle the next request without relying on its own prior request history; durable state may still live in an external database or session store. A stateful component owns evolving information needed for correctness, so replacement requires replication, checkpoint recovery, replay, or reassignment.
How to think about it
A stateless compute instance does not need its own previous request history. Any healthy replica can serve the next call because sessions, carts or workflow state live in shared durable systems.
A stateful component owns information that participates in correctness: database pages, stream-processor windows, workflow cursors or a local index. Scaling and recovery therefore involve partition ownership, consistency, replication and restore—not only load balancing.