AWS Cloud Developer Associate Certification

3. ELB and ASG

There are three types of Elastic Load Balancer (ELB) on AWS:

• Classic Load Balancer (CLB) – this is the oldest of the three and provides basic load balancing at both layer 4 and layer 7.
• Application Load Balancer (ALB) – layer 7 load balancer that routes connections based on the content of the request
• Network Load Balancer (NLB) – layer 4 load balancer that routes connections based on IP protocol data.

Elastic Load Balancing

• An ELB forwards traffic to eth0 (primary IP address).

EC2 Auto Scaling

• Auto Scaling can span multiple AZs within the same AWS region
• Auto Scaling is a region-specific service.
• There is no additional cost for Auto Scaling, you just pay for the resources
• You cannot edit a launch configuration once defined
• You can use a launch configuration with multiple Auto Scaling Groups (ASG).

EC2 Auto Scaling – Scaling Option

Scaling Option	What it is	When to use
Maintain
Manual
Scheduled
Dynamic

EC2 Auto Scaling – Scaling Types (associated with Dynamic Scaling Policies)

Scaling	What is it	when to use
Target Tracking Policy
Simple Scaling Policy
Step Scaling Policy

EC2 Auto Scaling – Health Checks

• By default uses EC2 status checks
• Can also use ELB health checks and custom health checks
• If any health check returns an unhealthy status the instance will be terminated.
• With ELB an instance is marked as unhealthy if ELB reports it as OutOfService
• If an instance is marked as unhealthy it will be scheduled for replacement.