• Balances load accross multiple web-server instances.

Types of ELB

  • Application Load Balancer
  • Network Load Balancer
  • CLassic Load Balancer

Application Load Balancer

  • Operates on OSI layer 7 of computing and are application-aware, ie. can make decision based on application sending the request.
  • Can see upto layer 7 to make routing decisions.
  • Best suited for http and https traffic.
  • Can create advanced request routing, sending specified requests to specific web servers.

Network Load Balancer

  • Operates at connection level on OSI layer 4 of computing.
  • Superfast performance and superfast speed ie. low latency.
  • Most expensive load balancer, generally used in Production.
  • Best suited for tcp traffic requiring extreme performance.
  • Capable of handling millions of requests per second, while maintaining ultra-low latencies.

Classic Load Balancer

  • Legacy elastic load balancer - important for aws certification
  • Can load-balance http/https applications and uses layer-7 specific features, such as X-Forwarded and sticky sessions.
  • Can also use strict layer 4 load balancing for applications that rely purely on the TCP protocol.
  • Error
    • If your application stops responding, the ELB responds with a 504 error.
    • This implies application is having issues, could be either on web server layer or database layer.
    • Identify the point of faliure and scale up/scale out where possible.

X-Forwarded-For Header

  • To get ipv4 address of your end user.

x-forwarded-for