How to implement load balancing strategies
· Category: Networking
Short answer
Load balancing distributes incoming network traffic across multiple servers to prevent any single server from becoming a bottleneck. Common algorithms include round robin, least connections, and IP hash. A load balancer sits between clients and servers, routing requests based on the chosen strategy. For how this fits into larger architectures, see how caching improves system performance.
Common algorithms
- Round robin — Requests go to each server in turn. Simple, fair distribution but ignores server load.
- Least connections — Sends traffic to the server with fewest active connections. Better when requests vary in duration.
- IP hash — Hashes the client IP to consistently route to the same server. Useful for session persistence.
- Weighted round robin — Assigns weights to servers based on capacity. More powerful servers get more traffic.
- Least response time — Routes to the server with the fastest response time and fewest active connections.
Layer 4 vs Layer 7
- Layer 4 (transport): Balances based on IP and port. Fast, doesn't inspect content. Example: TCP load balancer.
- Layer 7 (application): Inspects HTTP headers, cookies, URLs. Can route based on path (
/api/*→ API servers,/images/*→ CDN). Slower but more flexible.
Health checks
Load balancers must detect unhealthy servers and stop sending them traffic:
- Active health checks: Periodically send requests to each backend (e.g., GET /health every 10s)
- Passive health checks: Mark a server as down after N consecutive failures
Tips
- Always configure health checks — a dead server receiving traffic is worse than no server at all
- Use Layer 7 for HTTP applications when you need path-based routing; for understanding DNS's role, see how to configure DNS records
- For global traffic distribution, consider DNS-based load balancing or how CDNs speed up content delivery