Elastic Load Balancing in a VPC

Elastic Load Balancing (ELB) automatically distributes incoming traffic across multiple targets — EC2 instances, containers, IP addresses, or Lambda functions — within your VPC. It improves availability by spreading load across Availability Zones and ensures that no single resource becomes a bottleneck. Understanding how ELB integrates with VPC networking is essential for any production architecture.

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Why Load Balancing?

Without a load balancer:

• Users connect directly to a single server — if it fails, they get an error.
• You cannot scale horizontally; adding servers means changing DNS or client configuration.
• SSL termination, health checks, and request routing must be handled by the application.

With a load balancer:

• Traffic is distributed across multiple healthy targets.
• Unhealthy targets are automatically removed from rotation.
• You can scale in and out by adding or removing targets — the load balancer adapts.
• SSL termination can be offloaded to the load balancer.

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Types of Elastic Load Balancers

AWS offers three types of load balancers, each designed for different use cases: