AWS - Elastic Load Balancer (ELB)

• Application Load Balancer
• Best suited for HTTP and HTTPS traffic.
• Operate at layer-7 and are application aware.
• They are intelligent and your can create advanced request routing, sending specified requests to specific webservers.
• Network Load Balancer
• Best suited for TCP traffic where extreme performance is required.
• Operate at connection level (Layer-4).
• Can handle millions of requests per second with very-low latency.
• Used for extreme performance.
• Classic Load Balancer (Elastic Load Balancer)
• Are the legacy Elastic Load Balancers.
• Can use for HTTP/HTTPS applications
• Use layer-7 specific features such as X-Forwarded-for header and sticky sessions.
• You can also use strict layer-4 load balancing for applications that rely purely on TCP protocol.
• 504 error means application has timed out. That means Load Balancer is still there but it is not able to connect to any application server.
• If you want IP address of your users, look for X-Forwarded-for header.
• Instances monitored by ELB are reported as InService and OutofService.
• Health checks check the Instance’s health by talking to it.
• Load balancers have their own DNS name and you are never given the IP address