Load balancers preview

Elastic Load Balancing distributes traffic across targets. Application Load Balancer (ALB) handles HTTP/HTTPS at Layer 7; Network Load Balancer (NLB) handles TCP/UDP at Layer 4 with extreme performance.

ALB features

• Path-based routing (/api/* → one target group)
• Host-based routing (api.example.com)
• Health checks remove unhealthy EC2/tasks
• SSL termination at the load balancer

Typical architecture

Internet → ALB (public subnets) → EC2/ECS tasks (private subnets) → RDS. Django behind Gunicorn registers as ALB target on port 8000.

List load balancers

aws elbv2 describe-load-balancers \
  --query 'LoadBalancers[].{Name:LoadBalancerName,Type:Type,DNS:DNSName}' \
  --output table

Practice: Create S3 buckets and VPC resources only in a sandbox account. Use unique bucket names globally; delete buckets and empty objects when finished.

Cost: ALB/NLB bill hourly plus LCU usage—delete sandbox load balancers when done.

Important interview questions and answers

1. Q: ALB vs NLB?
   A: ALB for HTTP routing and host/path rules; NLB for low-latency TCP/UDP passthrough.
2. Q: Health check purpose?
   A: Stop sending traffic to failed instances until they recover or are replaced.

Self-check

1. What layer does an ALB operate at?
2. Why terminate SSL at the load balancer?

Tip: Delete sandbox ALBs when done—they bill hourly even with no traffic.