Load Balancing Strategies for AWS Solutions Architect Professional
Why Load Balancing Strategies Matter
Load balancing is a critical component of building highly available, scalable, and fault-tolerant architectures on AWS. For the Solutions Architect Professional exam, understanding load balancing strategies is essential because it directly impacts application performance, user experience, and cost optimization. Questions often require you to choose the most appropriate load balancing solution for complex, real-world scenarios.
What is Load Balancing?
Load balancing is the process of distributing incoming network traffic across multiple targets, such as EC2 instances, containers, IP addresses, or Lambda functions. AWS offers several load balancing options:
Application Load Balancer (ALB) - Operates at Layer 7 (HTTP/HTTPS), ideal for microservices and container-based applications. Supports path-based and host-based routing, WebSockets, and HTTP/2.
Network Load Balancer (NLB) - Operates at Layer 4 (TCP/UDP/TLS), capable of handling millions of requests per second with ultra-low latency. Provides static IP addresses and preserves source IP.
Gateway Load Balancer (GWLB) - Operates at Layer 3 (Network layer), designed for deploying and scaling third-party virtual appliances like firewalls and intrusion detection systems.
Classic Load Balancer (CLB) - Legacy option operating at both Layer 4 and Layer 7, primarily for EC2-Classic networks.
How Load Balancing Works in AWS
Target Groups: Define where traffic is routed. Targets can be instances, IP addresses, Lambda functions, or other ALBs.
Listeners: Check for connection requests using configured protocols and ports, then forward traffic based on defined rules.
Health Checks: Continuously monitor target health and route traffic only to healthy targets.
Cross-Zone Load Balancing: Distributes traffic evenly across all registered targets in all enabled Availability Zones.
Sticky Sessions: Bind user sessions to specific targets for stateful applications.
Connection Draining (Deregistration Delay): Allows in-flight requests to complete before deregistering targets.
Advanced Load Balancing Strategies
Weighted Target Groups: ALB supports weighted routing to distribute traffic percentages across different target groups, useful for blue-green deployments and canary releases.
Slow Start Mode: Gradually increases traffic to newly registered targets, preventing overwhelming new instances.
Lambda as Target: ALB can invoke Lambda functions, enabling serverless architectures behind load balancers.
PrivateLink Integration: NLB integrates with AWS PrivateLink to expose services to VPC endpoints.
Global Accelerator: Provides static anycast IP addresses and routes traffic to optimal AWS endpoints based on health, geography, and routing policies.
Exam Tips: Answering Questions on Load Balancing Strategies
1. Identify the OSI Layer requirement: If the question mentions HTTP headers, cookies, or URL paths, think ALB. For TCP/UDP traffic, extreme performance, or static IPs, consider NLB.
2. Look for latency keywords: Ultra-low latency requirements typically point toward NLB, which can handle millions of requests with minimal delay.
3. Security appliance scenarios: When questions involve deploying firewalls, IDS/IPS, or traffic inspection, GWLB is the answer.
4. Static IP requirements: NLB provides static IP addresses per AZ. ALB requires using Global Accelerator for static IPs.
5. WebSocket and HTTP/2: These protocols require ALB, not NLB or CLB.
6. Preserve source IP: NLB preserves client source IP by default. ALB uses X-Forwarded-For headers.
7. Blue-green and canary deployments: Look for ALB with weighted target groups or Route 53 weighted routing policies.
8. Cross-region failover: Combine load balancers with Route 53 health checks or use Global Accelerator.
9. Cost optimization: Consider whether the scenario truly requires a load balancer or if other solutions like Auto Scaling alone might suffice.
10. Read carefully for hybrid scenarios: Questions involving on-premises integration may require NLB with IP-based targets or Direct Connect considerations.