Load Balancers (ELB)

Load Balancer types

• Application Load Balancers - best suited for load balancing of HTTP and HTTPS traffic, operate at Layer 7 and **are application-aware, intelligent, create advanced request routing, sending specified requests to secific web servers

  

• Network Load Balancers - best suited for load balancing of TCP traffic where extreme performance is required, operate at the connection level, Layer 4, can handling millions of requests per second, while maintaining ultra-low latencies

  • directly see the client IP

  

• Classic Load Balancers - legacy Elastic Load Balancers, can use for load balance HTTP/HTTPS applications and use Layer 7 - specific features (X-Forwarded, sticky session), can strict Layer 4 load balancing for app that rely purely on the TCP protocol

Application LB + Class LB

• error 504 - time out error ⇒ need to trouble shoot the application failed (web server or database server?)
• X-Forwarded-For Header

EC2 instance look to X-Forwarded-For header to know origin IP (User IP)

• EC2 instance look to X-Forwarded-Port header to know origin port
• EC2 instance look to X-Forwarded-Protol header to know origin protocol

Tips

• instances monitored by ELB are reported as: InService, Outof Service
• health check checks the instance health by talking to it
• Load balances have their own DNS name (not IP)

Advanced Load Balancer Theory (ALB + CLB)

• Sticky Sessions (Stickiness): enable your users to stick to the same EC2 instance. useful if you are storing information locally to that instance (cache...)