AWS Elastic Load Balancer (ELB)

AWS offers four ELB types: Application Load Balancer (ALB) for HTTP/HTTPS traffic at Layer 7, Network Load Balancer (NLB) for TCP/UDP traffic at Layer 4, Gateway Load Balancer (GWLB) for third-party network appliances, and Classic Load Balancer (CLB) for legacy applications. Each type is optimized for different traffic patterns and use cases. The Classic Load Balancer is being phased out in favor of the newer options.

Yes, Application Load Balancers natively support WebSocket and Server-Sent Events without additional configuration. The ALB upgrades incoming HTTP connections to WebSocket and maintains the connection as long as it remains active. Classic Load Balancers also support WebSocket but with fewer features and less control.

AWS charges for ELB based on an hourly rate per active load balancer instance plus a per-GB data processing fee for traffic flowing through it. Pricing varies by AWS region and by load balancer type—ALB and NLB have different rate structures. You also pay standard data transfer fees for traffic leaving AWS.

Yes, you can register on-premises targets with Application Load Balancers and Network Load Balancers by using AWS Outposts or by connecting on-premises servers via VPN or Direct Connect with IP-address-based target registration. This enables hybrid architectures where traffic is load balanced across cloud and on-premises resources.