AWS Load Balancing Overview

• Definition: A load balancer is a server or a set of servers that distribute incoming network traffic across multiple backend EC2 instances.
• Purpose: It ensures that no single server bears too much demand. By spreading the load, it increases the application's responsiveness and availability.

Key Points

• Elastic Load Balancer (ELB): A set of servers that manage the incoming traffic and distribute it to EC2 instances.
• User Transparency: Users connect to the ELB rather than directly to backend instances, unaware of which instance is serving them.
• Benefits of Using Load Balancers:
  • Spreads load across multiple instances.
  • Provides a single point of access to applications.
  • Handles failures of instances seamlessly with health checks.
  • Offers SSL termination for secure HTTPS traffic.
  • Enforces stickiness with cookies.
  • Ensures high availability across zones.
  • Separates public and private traffic.

AWS Managed Load Balancers

• Managed Service: AWS handles upgrades, maintenance, and availability.
• Cost-Effective: Cheaper than setting up a personal load balancer.
• Scalability: Automatically scales with traffic.
• Integration: Works with EC2, Auto Scaling groups, ECS, Certificate Manager, CloudWatch, Route 53, WAF, Global Accelerator, etc.

Health Checks

• Function: Determines if an EC2 instance is functioning correctly.
• Mechanism: Uses a specified port and route (e.g., /health) to check the instance.
• Response Handling: If an instance fails to return a 200 OK status, it is marked unhealthy and won't receive traffic.

Types of Load Balancers

• Classic Load Balancer (CLB): Older generation, supports HTTP, HTTPS, TCP, SSL/TLS. AWS recommends against using CLB.
• Application Load Balancer (ALB): Supports HTTP, HTTPS, WebSocket. Recommended for modern applications.
• Network Load Balancer (NLB): Supports TCP, TLS, UDP. Suitable for high-performance networking.