Load Balancer

A load balancer is a device or service that spreads incoming network traffic across several servers so that no single server is overloaded. Users connect to the load balancer's address, and it forwards each request to one of the healthy servers behind it, skipping any that fail health checks.

Common methods are round robin (each server in turn), least connections and IP hash (the same user always goes to the same server). Layer 4 load balancers route by IP address and port; layer 7 load balancers can route by URL, header or cookie. Load balancing improves speed, reliability and the ability to scale by adding servers.