04 - Elastic Load Balancer

Question 1

Three types of load balancers

Answer 1

Three types of load balancers

• Application Load Balancers
• Network Load Balancers
  
  • Support static IP addresses
  • Support elastic IP addresses
  • Preserve Private Source IP addresses
• Classic Load Balancers (same as elastic load balancer)

Question 2

504 Error

Answer 2

504 Error - Classic Load Balancer Errors

• Means the gateway has timed out
• Does not mean that it is the LB timing out
• This means the application has not responded within the idle timeout period (check web application or database)

Details

• If the application stops responding, the elastic load balancer (ELB) responds with a 504 Error (gateway timeout) (e.g. the application is having issues)
• The error is not with the ELB, but with the Web Server Layer or the Database Layer (identify problem and scale up / out as needed)

Question 3

X-Forwarded-For Header

Answer 3

• Used by Classic Load Balancers
  
  • Uses X-Forwarded & Sticky Sessions (not as intelligent as the Application Load Balancer)
  • X-Forwarded-For Header
    
    • By default the ELB only send its private address to the endpoint (it is the man in the middle)
    • The X-Forwarded-For Header contains the public IP address of the requestor

Question 4

7 Layers of OSI Model

Answer 4

Question 5

Load Balancer Details

Answer 5

Application Load Balancers (preferred for HTTP / HTTPS)

• Best for a flexible feature set for your web applications with HTTP and HTTPS traffic.
• They operate at the request level (Layer 7 of the OSI Model)
• Application Load Balancers provide advanced routing, TLS termination and visibility features targeted at application architectures, including microservices and containers.

Network Load Balancers (new) (preferred for TCP)

• Best for when you need ultra-high performance and static IP addresses for your application.
• Operating at the connection level (Layer 4 of the OSI Model)
• Network Load Balancers are capable of handling millions of requests per second while maintaining ultra-low latencies.

Classic Load Balancers (old) (combined load balancing for HTTP / HTTPS / TCP / TLS) (THIS IS ON THE EXAM)

• Legacy solution
• Best for when you have an existing application running in the EC2-Classic network
• They operate at the request level (Layer 7 of the OSI Model - Application Aware)
• They are intelligent routing decisions at either the transport layer (TCP / SSL) or the application layer (HTTP / HTTPS)
• It supports either EC2-Classic or a VPC
• Can support strict layer 4 load balancing for applications that rely purely on the TCP protocol