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Application Load Balancer

Overview​

Application Load Balancer (ALB) is a powerful AWS service that distributes incoming application traffic across multiple targets based on content-based routing rules. It supports features like SSL/TLS termination, health checks, sticky sessions, and integration with AWS services, making it suitable for handling diverse and complex application traffic needs. ALB is particularly well-suited for modern web applications, microservices, and APIs, offering advanced routing capabilities and scalability.

Key Features​

  • It operates at the application layer (Layer 7) of the OSI model, which allows it to make routing decisions based on the content of the request.
  • Supports Content-Based Routing, Host-Based Routing, source IP Address, query string parameter-based routing
  • Support instances, IP addresses, Lambda Functions, and containers as targets
  • SSL/TLS Termination
  • Health Checks
  • Sticky Sessions
  • WebSocket Support
  • Integration with AWS Services
  • Traffic Filtering through Security Groups

Use Cases​

1. Microservices Architectures:

  • Service Routing: ALB can route requests to different microservices based on URL paths or hostnames, making it ideal for applications built using microservices.

2. Web Applications:

  • Traffic Distribution: Distribute incoming HTTP/HTTPS traffic across multiple instances or containers, ensuring even load distribution and high availability.

3. API Gateways:

  • API Management: Use ALB to route API requests to different backend services based on the request content, providing a robust API management solution.

4. Hybrid Environments:

  • Cross-Region Routing: Implement cross-region load balancing by routing traffic to different regions based on the request, optimizing performance and resilience.

Analogy​

Application Load Balancer (ALB) is like a traffic manager at a busy intersection who directs vehicles (requests) based on their destination (content). Just as a traffic manager directs cars to different lanes or exits based on where they need to go, ALB directs incoming traffic to various backend services based on URL paths, hostnames, or other content in the request.