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
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
- Real-time multiplayer games: Low-latency in-memory game state per connection benefits from a persistent stateful server.
- Database transactions: Multi-step transactions need the connection to remember uncommitted work until commit or rollback.
- Streaming media sessions: Protocols like RTSP or WebSockets keep a live connection open with ongoing playback state.
Stateless
- Public REST APIs: Stateless requests let any server or region handle calls without session affinity.
- Auto-scaling web services: New instances can join a pool instantly since no server holds unique session data.
- Serverless functions: Ephemeral compute like Lambda fits stateless design since instances are created and destroyed freely.