A solutions architect needs to design a highly available web application across multiple Availability Zones. Which Elastic Load Balancer type operates at the application layer?

Correct answer: Application Load Balancer

Option B is correct because the Application Load Balancer (ALB) operates at Layer 7 of the OSI model, the application layer, and supports HTTP/HTTPS routing, path-based routing, host-based routing, and WebSocket connections, making it ideal for highly available web applications. Option A, the Classic Load Balancer, is a legacy product that operates at both Layer 4 and Layer 7 but lacks the advanced routing features of the ALB and is not recommended for new architectures. Option C, the Gateway Load Balancer, operates at Layer 3 and is designed to route traffic through third-party virtual network appliances such as firewalls and intrusion detection systems, not web applications. Option D, the Network Load Balancer, operates at Layer 4 (transport layer) and is optimized for high-performance, low-latency TCP/UDP traffic, not application-layer HTTP routing.