Stateless vs. Stateful Load Balancing - Key Differences and Use Cases

• What Is Stateless Load Balancing?
• What Is Stateful Load Balancing?
• 🧠 Types of Stateful Load Balancing
• Stateless vs. Stateful Load Balancing: A Comparison
• When to Use Which?
• Conclusion

When designing scalable systems, one of the most critical decisions you'll face is how to distribute traffic across your servers. Two core models are widely used: stateless and stateful load balancing.

But which one is right for your application?

This guide breaks down the differences, examples, and use cases of stateless and stateful load balancers to help you make the right architecture decision.

What Is Stateless Load Balancing?

Stateless load balancing distributes incoming traffic without retaining any client session information. Each request is treated independently—no memory of past interactions, sessions, or assigned servers.

🔧 How It Works:

• Routing decisions are made using attributes like:

  • IP address
  • Request URL
  • HTTP headers

• No tracking of user sessions or history

📦 Example:

An e-commerce search page that returns product results based on location:

• A stateless load balancer routes requests to the nearest server using geo-based routing.
• No session persistence is needed—each search is independent.

✅ Pros:

• Scalable: Easily adds/removes servers without session concerns
• Fast: Minimal overhead
• Simple to manage: Statelessness means no session tracking logic

⚠️ Cons:

• Not suitable for applications requiring session context (e.g., user login, shopping carts)

What Is Stateful Load Balancing?

Stateful load balancing maintains session awareness. It ensures that a user's requests are always sent to the same backend server, enabling access to session data like login state or preferences.

🔧 How It Works:

• Tracks user sessions using identifiers like:

  • Client IP (Source IP Affinity)
  • Cookies or session tokens (Session Affinity)

• Ideal for apps that depend on persistent state

📦 Example:

A user logs into their account on a banking app:

• A stateful load balancer directs all subsequent requests to the same backend server.
• The session containing login info and account data stays intact.

🧠 Types of Stateful Load Balancing

🔁 1. Source IP Affinity

• Binds a client to a server based on IP address
• Simple but can break when IP changes (e.g., mobile devices, proxies)

🍪 2. Session Affinity (Sticky Sessions)

• Uses cookies or tokens to track the user session
• More reliable across dynamic IPs or mobile clients

Stateless vs. Stateful Load Balancing: A Comparison

When to Use Which?

Conclusion

Choosing between stateless and stateful load balancing depends on your application's architecture and user experience needs:

• 🧪 Use stateless for performance, simplicity, and scalable services that don't depend on session data.
• 🔒 Use stateful for session-sensitive applications that require consistent backend assignment.

Pro tip: For high availability and user session resilience, consider combining stateful load balancing with distributed session stores like Redis or implementing sticky sessions with smart fallbacks.