Cross Zone Load Balancing in AWS

Key Concepts:

• Cross Zone Load Balancing: Allows each load balancer instance to distribute incoming traffic evenly across all registered instances in all availability zones.

Scenarios:

1. With Cross Zone Balancing:
   • Traffic is distributed evenly across all EC2 instances.
   • If a client sends 50% of traffic to each of two ALB instances, each EC2 instance will receive an equal share of the traffic (10% each if there are 10 instances).

1. Without Cross Zone Balancing:
   • Traffic is distributed only among EC2 instances within the same availability zone as the ALB instance.
   • If there is an imbalance in the number of EC2 instances across availability zones, some instances may receive more traffic than others.

Load Balancer Types and Default Settings:

• Application Load Balancer (ALB):
  • Cross zone load balancing is enabled by default.
  • No additional charges for inter-AZ data transfer.
• Network Load Balancer (NLB) and Gateway Load Balancer (GLB):
  • Cross zone load balancing is disabled by default.
  • Enabling it may incur additional charges due to inter-AZ data transfer.
• Classic Load Balancer (CLB):
  • Cross zone load balancing is disabled by default.
  • Enabling it does not incur charges for inter-AZ data transfer.
  • CLB is considered previous generation and will be retired soon.

Practical Steps:

• For NLB and GLB:
  • Cross zone load balancing can be enabled in the attributes section, which may result in regional charges.
• For ALB:
  • Cross zone load balancing is on by default and can be adjusted at the target group level.
  • You can inherit settings from the load balancer attributes or override them for a specific target group.

Next Steps:

• Ensure understanding of how to configure cross zone load balancing for different types of load balancers.
• Practice setting up and modifying load balancer attributes and target group settings in the AWS Management Console.