AWS Elastic Load Balancing distributes incoming traffic across multiple targets to improve availability and scalability for web applications. The service provides different load balancer types tailored to specific network, performance, and security requirements.
Application Load Balancer, Network Load Balancer, and Gateway Load Balancer each serve distinct use cases. Understanding their differences helps architects select the right option for latency, throughput, and protocol handling needs.
| Load Balancer Type | Primary Layer | Key Protocols | Best For |
|---|---|---|---|
| Application Load Balancer (ALB) | Layer 7 | HTTP, HTTPS | Web and microservices traffic with advanced routing |
| Network Load Balancer (NLB) | Layer 4 | TCP, UDP, TLS | High performance, static IP, ultra low latency |
| Gateway Load Balancer (GWLB) | Layer 2/3 | Transparent integration | Third party virtual appliances and security services |
| Use Case Example | Traffic Management | Target Types | Routing Logic |
| ECS, Kubernetes, Lambda | Container and serverless apps | Containers, IP addresses | Path-based and host-based routing |
Understanding Application Load Balancer Behavior
The Application Load Balancer operates at the application layer, inspecting HTTP and HTTPS headers to make routing decisions. It supports path-based and host-based routing, enabling multiple domains and applications on the same IP.
ALB integrates tightly with containers and serverless platforms, supporting target groups for ECS, Kubernetes, and Lambda. Health checks automatically route traffic away from unhealthy instances to maintain high availability.
Leveraging Network Load Balancer for Performance
The Network Load Balancer functions at Layer 4, handling millions of requests per second with minimal latency. It preserves the source IP address and supports static Elastic IPs for predictable firewall rules.
NLB excels for TCP and UDP workloads such as databases, gaming servers, and enterprise appliances. It offers target failover across Availability Zones and supports TLS termination for encrypted traffic.
Deploying Gateway Load Balancer for Security
Gateway Load Balancer extends Layer 2 connectivity for third party virtual appliances like firewalls and intrusion detection systems. It enables transparent inspection without requiring changes to IP addresses or VLAN topology.
GWLB combines the benefits of a security appliance with cloud elasticity, allowing traffic to pass through monitored and inspected paths. Teams can centrally manage security policies while retaining high throughput and low latency.
Architectural Differences and Selection Criteria
Selecting the right load balancer involves evaluating protocol support, latency requirements, and integration with existing infrastructure. ALB suits web and API traffic, while NLB fits high performance and static IP needs.
Consider GWLB when you need to route traffic through security appliances without redesigning the network. Each balancer type brings distinct billing models, connection limits, and scaling behaviors that impact cost and operations.
Operational Best Practices for Elastic Load Balancing
- Define clear target groups and health check paths for each load balancer type.
- Use connection draining on ALB to complete in flight requests during deregistration.
- Configure security groups and listeners to enforce least privilege access.
- Monitor metrics such as request count, latency, and error rates to detect issues early.
- Align load balancer selection with traffic patterns, IP requirements, and compliance needs.
FAQ
Reader questions
How do I choose between ALB and NLB for a microservices architecture?
For microservices requiring content based routing and container integration, choose ALB. For extreme performance, static IPs, or non HTTP protocols, choose NLB.
Can I use NLB to preserve client source IP without proxy protocol?
Yes, NLB preserves the original client IP at the target without requiring proxy protocol configuration on most setups.
Does GWLB add extra hops or latency compared to traditional appliances?
GWLB is optimized for low latency and avoids extra hops by integrating directly with the VPC data plane while still providing inspection capabilities.
What happens to existing connections during target failover on ALB and NLB?
Ongoing TCP connections may be reset during failover, while new connections are routed only to healthy targets based on health check status.