AWS Elastic Load Balancer

Distributes incoming traffic across multiple targets, such as

  • EC2 instances

  • Containers

  • IP addresses

  • Lambda functions

  • Must have at least 2 AZ’s to make use of it.

  • Sticky sessions X-forwarded-For (XFF) header illustration of XFF header in use

  • With regard to ELB health checks, when an instance is considered unhealthy, ELB doesn’t terminate it, it merely redirects the traffic to healthy instances.

  • Cross Zone load balancing - only available for ALB & CLB.

    • I wonder, why doesn’t it work for network load balancer?

  • ELB’s cannot go cross region. one per region

  • ALB is good for web applications

  • NLB is good for high throughput, eg video games

3 Types of load balancer

  1. Application Load Balancer (HTTP(s)). Params you can apply rules on:
    • host header
    • source ID
    • path
    • http headers
    • http header method
    • query string
  2. Network Load Balancer (TCP/UDP)
  3. Classic Load balancer - this bad boy’s considered legacy now.