AWS Application Load Balancer (ALB) Overview

• Layer 7 Load Balancer: ALB operates at the application layer, handling HTTP/HTTPS traffic.
• Target Groups: Routes traffic to groups of resources, such as EC2 instances, ECS tasks, Lambda functions, or private IP addresses.
• Container and Microservices Support: Ideal for container-based applications using ECS due to port mapping features for dynamic ports.
• Advanced Routing: Capable of routing based on URL path, hostname, query strings, and headers.
• HTTP/2 and WebSocket Support: ALB supports modern web protocols for efficient communication.
• Automatic Redirects: Can automatically redirect HTTP traffic to HTTPS for secure communication.
• Health Checks: Performs health checks at the target group level to ensure traffic is only routed to healthy targets.
• Serverless Integration: Can route traffic to AWS Lambda functions for serverless architectures.
• Fixed Hostname: Provides a consistent DNS name for the load balancer.
• Client IP Preservation: Uses X-Forwarded-For, X-Forwarded-Ports, and X-Forwarded-Proto headers to pass the original client IP and protocol information to the backend.

Example Scenario

• Public Facing ALB: Serves as the entry point for incoming web traffic.
• Multiple Target Groups:
  • /user path routes to a target group with EC2 instances for user-related services.
  • /search path routes to a different target group with EC2 instances for search services.
• Routing Rules: ALB uses rules to direct traffic to the appropriate target group based on the request path, hostname, or query parameters.
• Use Case for Query String Routing:
  • Mobile traffic with ?Platform=Mobile in the URL is routed to one target group.
  • Desktop traffic with ?Platform=Desktop is routed to another target group.

Preparing for Hands-On

• Fixed Hostname: ALB provides a stable DNS name.
• Client IP Headers: The backend servers access the client's IP through specific HTTP headers due to the load balancer's connection termination.