Infrastructure
Design Sticky Sessions
Sticky sessions ensure a user's requests are routed to the same server instance throughout their session. This design covers load balancer strategies, session replication, and failover mechanisms.
- Problem â Stateful applications need request affinity
- Solution â Load balancer routing with session persistence
- Trade-off â Simpler state management vs load imbalance
Sticky sessions are a pragmatic solution for legacy applications that cannot be made stateless.
What Are Sticky Sessions?
Why Sticky Sessions?
Load Balancer Strategies
Session Replication
Replication Strategies
Failover Scenarios
Trade-offs
| Aspect | Sticky Sessions | Stateless |
|---|---|---|
| State Management | Simple (in-memory) | Complex (external store) |
| Load Balance | Uneven (hot servers) | Even distribution |
| Failover | Session loss risk | Seamless |
| Scalability | Limited by session state | Horizontal scaling |
| Complexity | Low | High |
When to Use Sticky Sessions
Practice Exercises
- Design: How would you implement sticky sessions with automatic failover when a server crashes?
- Scale: Design a sticky session system for 10M concurrent users across 100 servers.
- Migration: How would you migrate from sticky sessions to a stateless architecture without downtime?
- Consistency: Design a session replication system with < 100ms propagation delay.
What to Learn Next
-> Load Balancing Distribution algorithms and strategies.
-> Caching Strategies Distributed session caching.
-> Circuit Breaker Server failure handling.
-> Retry Patterns Resilient session recovery.
-> Sidecar Pattern Service mesh session management.
-> Strangler Fig Migrating from sticky sessions.