Stateful vs Stateless: Where the Session Lives
Overview This comparison covers whether a server or protocol retains session state between requests, or treats every request as a fully self-contained unit with no memory of prior ones. The choice determines how you scale, fail over, and route traffic across instances. Comparison Diagram StatefulStatelessClientServer Asession: id=42must returnto same serverServer Bno session dataClientcarries tokenServerServerany server canhandle the requestStateful: server pins session context and routing depends on itStateless: request carries all context, any node can serve it Comparison Table Aspect Stateful Stateless Request context Server retains prior interaction data across requests Each request carries all context needed to process it Session storage Held in server memory or local session store None on server; state lives in client token or database Routing requirement Requests must reach the same server (sticky sessions) Any server instance can handle any request Scaling model Vertical or sticky-session horizontal scaling only Trivial horizontal scaling, load balance freely Failure recovery Server crash loses in-memory session unless replicated Server crash has no session impact, retry hits any node Client design Client can be thin, server tracks progress Client or token must resend full context each call Typical examples Database connections, WebSocket sessions, FTP REST APIs, HTTP with JWT, DNS lookups Key Differences Stateful servers keep session memory; stateless servers keep none between calls Stateless systems need no sticky routing, simplifying load balancers Stateful failover requires session replication to avoid data loss Stateless designs push state into the client or token instead of the server Horizontal scaling is near-free for stateless architectures When to Use Each Stateful ...