How do load balancers work, and what algorithms do they use?

Summary

Load balancers distribute requests across healthy backends using algorithms like round robin, least connections, weighted, or consistent hashing (for affinity), and remove unhealthy instances using health checks. L4 balancers route TCP/UDP connections; L7 balancers understand HTTP and can route by path, header or host.

Longer Answer

L7 features: TLS termination, path-based routing, retries, sticky sessions (avoid when possible), request buffering. Global load balancing (DNS/anycast) routes users to the nearest region.

Key Points

• Round robin / least connections / hashing
• Health checks
• L4 vs L7
• Avoid sticky sessions
• Global LB for regions