Distributes incoming application traffic across multiple targets, such as Amazon EC2 instances, containers, IP addresses, and Lambda functions.

• Can be physical hardware or virtual software.
• You can connect an SSL certificate to an ELB

<aside> 💡 An ELB must have at least two AZs

</aside>

<aside> 💡 An ELB cannot go cross-region, one per region

</aside>

Works in the following order:

1. Listeners
   • Traffic is evaluated against listeners. Evaluate any traffic that is matching the Listener’s port.
2. Rules — Not for CLB
   • Listeners will then invoke rules to decide what to do with the traffic.
3. Target Groups — Not for CLB

For ALB or NLB, ****traffic is sent to the Listeners. When the port matches it then checks the rules what to do. The rules will forward the traffic to a Target Group. The target group will evenly distribute the traffic to instances registered to that target group.

https://youtu.be/Ia-UEYYR44s?si=qcZ1JZzi8cAIr0_d&t=16004

• Classic Load Balancers — CLB — associated directly to the ASG

  • Can balance HTTPS, HTTPS or TCP traffic (not at the same time)
  • Layer 7, sticky sessions
  • Layer 4, strict balancing

  

  https://youtu.be/Ia-UEYYR44s?si=fb3My_S3u5kh4fs1&t=16064

• Application Load Balancer — ALB — associated indirectly to the ASG via their Target Groups

  • Operates at Layer 7 of the OSI Model, the Application layer
  • Designed to balance HTTP and HTTPS traffic
  • Request Routing, allows you to add routing rules to your listeners based on the HTTP protocol
  • Great for Web Applications

• Network Load Balancer — NLB — associated directly to the ASG via their Target Groups

  • Designed to balance TCP/UDP
  • Operates at Layer 4 of the OSI Model, the Transport layer
  • Can perform Cross-Zone Load Balancing
  • Great for Multiplayer Video Games, or when network performance is critical

Sticky Sessions

Is an advanced load balancing method that allows you to bind a user’s session to a specific EC2 instance.

This ensures that all requests from that session are sent to the same instance.

Typically utilized with a Classic Load Balancer

Can be enabled for ALB though can only be set on a Target Group, not individual EC2 instances.

Cookies are used to remember which EC2 instance.

Launch Configuration