Load Balancers and Stateless Services

L4 versus L7, health checks, statelessness

A load balancer distributes requests across servers and removes unhealthy ones using health checks. Layer 4 balancers route by IP and port (fast, protocol-agnostic); layer 7 balancers understand HTTP and can route by path or header, terminate TLS and retry. Algorithms include round robin, least connections and hashing for affinity. Keep application servers stateless (sessions in a shared store or tokens) so any server can handle any request and you can scale horizontally.

Spread load, avoid repeated work

Load balancers spread traffic, consistent hashing spreads data, and caches avoid repeated work.

A restaurant host

The host seats guests at whichever waiter has capacity and stops seating at a table whose waiter has gone home sick.

Make the balancer redundant too

Use managed balancers or active-passive pairs so the load balancer is not itself a single point of failure.

त्वरित जाँच: Why keep application servers stateless?

• So any server can handle any request and servers can be added or removed freely
• To make the code shorter
• Because databases require it
• To avoid needing a load balancer