Auto Scale Fargate Service Based On SQS ApproximateNumberOfMessagesVisible
I would like to scale out my aws fargate containers based on the size of the SQS queue. It appears that I can only scale based on the container's CPU or Memory usage. Is there a way to create a policy that would scale out and in based on queue size? Has anyone been able to scale based on other cloudwatch metrics?
Answer
Yes you can do this. You have to use a step scaling policy, and you need to have an alarm created already for your SQS queue depth (ApproximateNumberOfMessagesVisible).
Go to CloudWatch, create a new alarm. We'll call this alarm sqs-queue-depth-high, and have it trigger when the approximate number of messages visible is 1000.
With that done, go to ECS to the service you want to autoscale. Click Update for the service. Add a scaling policy and choose the Step Tracking variety. You'll see there's an option to create a new alarm (which only lets you choose between CPU or MemoryUtilization), or use an existing alarm.
Type sqs-queue-depth-high in the "Use existing alarm" field and press enter, you should see a green checkmark that lets you know the name is valid (i.e. the alarm exists). You'll see new dropdowns where you can adjust the step policy now.
This works for any metric alarm and ECS services. If you're going to be trying to scale this setup out, for multiple environments for example, or making it any more sophisticated than 2 steps, do yourself a favor and jump in with CloudFormation or Terraform to help manage it. Nothing is worse than having to adjust a 5-step alarm across 10 services.