Elastic Load Balancing (ALB, NLB, CLB)

Elastic Load Balancing (ELB) automatically distributes incoming traffic across multiple EC2 instances, containers, or IP addresses. Load balancers are essential for high availability, fault tolerance, and horizontal scaling. This lesson covers the three main types: Application Load Balancer (ALB), Network Load Balancer (NLB), and Classic Load Balancer (CLB).

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Why Load Balancers?

Without a load balancer, clients connect directly to individual instances. This creates several problems:

• Single point of failure — if the instance goes down, the service is unavailable
• Uneven load — some instances may be overwhelmed while others are idle
• No health checking — unhealthy instances continue receiving traffic
• Manual scaling — you must update DNS or client configuration when adding/removing instances

A load balancer solves all of these: