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AWS ELB

Types of Load Balancer

• Application Load Balancer [Layer 7]
• Network Load Balancer [Layer 4] - AWS most expensive
• Classic Load Balancer - legacy purposes - non-recommended

Application Load Balancers

• Best suited for load balancing of http and https traffic
• Operate at layer 7 and are application-aware
• Intelligent - you can create advanced request routing, sending specified requests to specific web servers

Network Load Balancers

• Best suited for load balancing of TCP traffic where extremer performance is required
• Operating at the connection level (Layer 4)
• Capable of handling millions of requests per second while maintaining ultra-low latencies
• Use for extreme performance. [most expensive to buy]

Classic Load Balancers

Legacy Elastic Load Balancers

• Load balance http/https applications and use 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
• If application stops responding the ELB responds with a 504 error.
• This means app is having issues - at either Web Server or Database Layer
• Identify where the application is failing, and scale it up or out where possible (504 err)

X-Forwarded-For Header

How to get IPv4 public address when load balancer sends EC2 the private address? Uses X-Forwarded-For header