What is the difference between stateful and stateless services?

Question

Accepted Answer

**Stateful** — stores client state. **Stateless** — no client state stored.

**Stateful:**
- Server stores session data.
- Client tied to specific server.
- Harder to scale.
- Sessions, shopping carts.

```
Stateful:
Client → Server A (session stored)
Client → Server A (must same server)
(State stored on server)
```

**Stateless:**
- No server-side state.
- Any server can handle request.
- Easy to scale.
- REST APIs, microservices.

```
Stateless:
Client → Any Server (state in token)
Client → Any Server (same result)
(No state on server)
```

**Key differences:**
- **Stateful** — stores state.
- **Stateless** — no state.
- **Stateful** — harder to scale.
- **Stateless** — easy to scale.

Systems Analyst: What is the difference between stateful and stateless services?