Understanding How ECS Autoscaling Works
If you’ve been using Amazon ECS long enough, you’ve probably at least heard of autoscaling. Horizontally scaling services, ECS or otherwise, is a huge part of building reliable web apps. When traffic spikes, you need more containers, and when it quiets down, you certainly don’t want to be paying for more than you need.
In this article, we’ll jump into how native ECS autoscaling works and examine its limitations. I’ll assume you already have an app running on ECS. If not, check out this guide on how to set up your ECS cluster with Terraform. Now let’s get into it!
The native ECS autoscaling functionality is pretty good. It does what it says it does, increasing and decreasing capacity according to a few compute metrics. It leans on CloudWatch metrics to decide when your services need a boost or a trim.
ECS automatically publishes a few service utilization metrics to AWS CloudWatch, which is how the autoscaler gets the metrics it needs to make scaling decisions. Whether the autoscaler is a feature of EC2 or a separate service depends on whether we’re dealing with autoscaling groups or service-level scaling, but we’ll get into that later.
