Load Balancer - Variations and Follow-ups

Variations

1. Layer 4 (TCP) Load Balancer

• Operates at transport layer
• Faster (no HTTP parsing)
• Protocol-agnostic
• Lower latency

2. Layer 7 (HTTP) Load Balancer

• Operates at application layer
• Content-based routing
• SSL termination
• Request modification

3. Global Load Balancer

• Geographic routing
• Multi-region failover
• Latency-based routing
• Disaster recovery

Follow-up Questions

Q: How do you handle session persistence?

Answer:

• Cookie-based (insert cookie with server ID)
• IP-based (hash client IP)
• Header-based (custom header)
• TTL for session timeout

Q: How do you detect unhealthy backends?

Answer:

• Active health checks (periodic probes)
• Passive health checks (monitor traffic)
• Mark unhealthy after N failures
• Remove from pool
• Re-add when healthy

Q: How do you handle backend server updates?

Answer:

• Connection draining
• Stop new connections
• Wait for existing to complete
• Timeout after N minutes
• Graceful shutdown

Q: How do you prevent overload?

Answer:

• Rate limiting per client
• Connection limits
• Queue requests
• Reject excess traffic
• Auto-scaling

This guide covers variations and deep-dive questions for load balancer interviews.