Stateless vs Stateful Services

Stateless vs Stateful Services

Stateless services do not retain client-specific state between requests, while stateful services persist session or workflow state. The choice affects scalability, availability, and operational complexity.

Stateless Services

Benefits:

• Horizontal scaling is straightforward.
• Failover is simple because any instance can serve any request.
• Deployment and autoscaling are low-risk.

Tradeoffs:

• Requires external state stores.
• May increase latency due to extra lookups.

Stateful Services

Benefits:

• Lower latency when state is local.
• Simplifies complex workflows that rely on in-memory state.

Tradeoffs:

• Harder to scale and fail over.
• Requires session affinity or sticky routing.
• More complex deployment strategies.

Spring Boot Example: Externalized Session State

@Configuration
@EnableRedisHttpSession
public class SessionConfig {
}

@RestController
@RequestMapping("/cart")
public class CartController {
    @PostMapping("/items")
    public ResponseEntity<Void> addItem(HttpSession session) {
        List<String> items = (List<String>) session.getAttribute("items");
        if (items == null) {
            items = new ArrayList<>();
        }
        items.add("item-1");
        session.setAttribute("items", items);
        return ResponseEntity.ok().build();
    }
}

Summary

Stateless services are easier to scale and operate, while stateful services can offer lower latency for specific workflows. Externalizing state often provides the best balance for modern cloud architectures.