Question

Hi. Does Amazon Elastic Load Balancing incorporate auto scaling?

That is: when the traffic drops to a low level from a high level, does it scale down?

Answer 1

Yes, it does.
According to the ELB product description,

Elastic Load Balancing automatically scales its request handling capacity in response to incoming application traffic.

Auto Scaling with Elastic Load Balancing

Let’s say that you want to make sure that the number of healthy Amazon EC2 instances behind an Elastic Load Balancer is never fewer than two. You can use Auto Scaling to set these conditions, and when Auto Scaling detects that a condition has been met, it automatically adds the requisite amount of Amazon EC2 instances to your Auto Scaling Group. Or, if you want to make sure that you add Amazon EC2 instances when latency of any one of your Amazon EC2 instances exceeds 4 seconds over any 15 minute period, you can set that condition, and Auto Scaling will take the appropriate action on your Amazon EC2 instances — even when running behind an Elastic Load Balancer. Auto Scaling works equally well for scaling Amazon EC2 instances whether you’re using Elastic Load Balancing or not.

As per the Auto Scaling feature description:

Auto Scaling allows you to scale your Amazon EC2 capacity up or down automatically according to conditions you define. With Auto Scaling, you can ensure that the number of Amazon EC2 instances you’re using increases seamlessly during demand spikes to maintain performance, and decreases automatically during demand lulls to minimize costs. Auto Scaling is particularly well suited for applications that experience hourly, daily, or weekly variability in usage.

Features of Auto Scaling

Scale out Amazon EC2 instances seamlessly and automatically when demand increases.
Shed unneeded Amazon EC2 instances automatically and save money when demand subsides.
Scale dynamically based on your Amazon CloudWatch metrics, or predictably according to a schedule that you define.