Application Load Balancer (ALB)

💡 Definition

An Application Load Balancer (ALB) is a type of Elastic Load Balancer that functions at the application layer (Layer 7 of the OSI model). It is best suited for load balancing HTTP and HTTPS traffic for modern application architectures, including microservices and containers.

🔑 Key Concepts

• Layer 7: Can inspect content of the request (headers, cookies, URL path) to make routing decisions.
• Path-Based Routing: Can route /images to one target group and /api to another.
• Host-Based Routing: Can route site-a.com to one group and site-b.com to another.
• Target Types: Can route to EC2 instances, Lambda functions, and IP addresses.

⚙️ How it Works

1. Listeners: You configure listeners (e.g., Port 80) to check for connection requests.
2. Rules: You define rules (e.g., "If URL path contains /api").
3. Routing: Traffic matching a rule is forwarded to a specific Target Group.

🎯 Use Cases

• Microservices: Routing traffic to different services based on the URL path.
• Containerized Apps: Deep integration with ECS and EKS.
• Web Applications: Handling HTTP/HTTPS traffic with advanced routing needs.

💰 Pricing Model

• Charged per Application Load Balancer-hour and per LCU (Load Balancer Capacity Unit) used.

📝 Exam Tips (CLF-C02)

• Think "Layer 7" (Application Layer).
• Think "HTTP/HTTPS".
• Supports Path-based and Host-based routing.
• Routes traffic to Target Groups.

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See Also: * Load Balancer * Target Group * Auto Scaling