Load Balancing Strategies: Algorithms and L4 vs L7 Differences

Load Balancing Strategies

Common Algorithms

Algorithm	Principle	Best For
Round Robin	Distribute in turn	Servers with similar capacity
Weighted Round Robin	Distribute by weight	Servers with different specs
Least Connections	Route to server with fewest active connections	Long-lived connections
IP Hash	Fixed routing based on client IP	Session sticky requirements
Random	Random assignment	Simple use cases

L4 vs L7 Load Balancing

L4 (Transport Layer)

• Based on TCP/UDP; doesn't inspect application content
• Faster performance
• Examples: AWS NLB, HAProxy in TCP mode

L7 (Application Layer)

• Based on HTTP/HTTPS; can inspect URL, headers, cookies
• Supports URL-based routing, SSL termination, A/B testing
• Examples: Nginx, AWS ALB, Kong

Health Checks

Load balancer periodically probes backend services and removes unhealthy nodes:

• Passive: Based on observed failure rate
• Active: Regularly sends dedicated health check requests