Application Load Balancer (ALB)

• Operates at Layer 7 (HTTP/HTTPS)

• Can distribute traffic to:
• Multiple HTTP applications across instances (target groups)
• Multiple applications on the same instance (e.g., containers)

• Supports HTTP/2 and WebSocket protocols

• Can perform redirects (e.g., HTTP → HTTPS)

• Ideal for microservices and containerized applications (e.g., Docker, Amazon ECS)

• Supports dynamic port mapping in ECS, allowing tasks to register with any available port

Advanced Routing Features

• Can route requests to different target groups based on:
• Path-based routing: /users → Users TG, /search → Search TG
• Host-based routing: app.example.com vs api.example.com
• Query string or header values: ?platform=mobile → TG1, ?platform=desktop → TG2

• Target groups can contain:
• EC2 instances (standalone or in an Auto Scaling Group)
• ECS tasks
• Lambda functions (HTTP request → JSON event)
• Private IP addresses (for hybrid on-prem routing)

• Health checks are configured at the target group level

• Supports routing across AWS and on-prem environments

Networking & Hostname

• ALB has a fixed DNS name: xxx.region.elb.amazonaws.com

• The original client IP is not directly visible to the target; instead:
• X-Forwarded-For → client IP
• X-Forwarded-Port → original client port
• X-Forwarded-Proto → original protocol (HTTP/HTTPS)