Elastic Load Balancing

Service that distributes access across multiple servers.

Load balancer service that distributes traffic across multiple targets. Includes ALB, NLB, and GWLB.

• Load balancing web applications
• Entry point for Multi-AZ architectures
• Removing unhealthy servers via health checks

• Distributes traffic across multiple targets
• ALB targets HTTP/HTTPS
• NLB targets high-performance TCP/UDP

• ALB supports path-based and host-based routing
• Design target groups and health checks
• Understand cross-zone load balancing

Elastic Load Balancing (ELB) is an AWS managed load balancer service that automatically distributes incoming traffic across multiple targets (EC2 instances / containers / Lambda functions / IP addresses). It comes in four types: ALB (Application Load Balancer), NLB (Network Load Balancer), GWLB (Gateway Load Balancer), and CLB (Classic Load Balancer), to be selected based on the layer and use case. ALB targets HTTP / HTTPS (Layer 7) and supports path-based, host-based, HTTP header, and query string routing. NLB targets TCP / UDP / TLS (Layer 4) and is suited for workloads that require ultra-low latency, high throughput, or static IP addresses. GWLB is a service specialized in inserting third-party virtual appliances (firewalls / IDS / IPS), while CLB is a legacy general-purpose load balancer. A typical configuration is to place an ALB in front of a group of EC2 instances spanning multiple AZs, combined with Auto Scaling, to ensure high availability and scalability for a web application. Health checks are performed per ALB target group, and instances that fail to respond are automatically removed. It is common to configure HTTPS listeners and associate ACM certificates so that TLS termination is performed at the ALB. In microservices architectures, it is widely adopted to associate multiple target groups with a single ALB and use path-based routing to dispatch /api to an API server, /static to static content, and the rest to a web server. In the exam context, CLF-C02 asks questions such as "which service distributes traffic across multiple servers?" and "which service is used at the entry point of a Multi-AZ configuration to improve availability?". SAA-C03 asks in depth about choosing between ALB and NLB (ALB for HTTP/HTTPS, NLB for ultra-low latency TCP/UDP), enabling cross-zone load balancing, sticky sessions, target group health check design, and combinations with WAF / CloudFront / Route 53.

• Elastic Load Balancing (AWS Official)
• What is Elastic Load Balancing (AWS Official Documentation)

Last updated: 2026-06-01