AWS Fargate service: scale to zero?
I've recently migrated a small web application to AWS using Fargate and Aurora Serverless. The application doesn't get much traffic so my goal is to save cost while no one is using it. Aurora Serverless seems to do this for me on the DB side automatically.
However, I'm struggling to find any resources on how to scale a Fargate service to zero.
There is an ALB in front of it and I know ALB request count can be used in scaling... so ideally when there is an average of 0 requests over a period of say 10 minutes, the service would scale down to zero tasks. Then when a request comes in, it would trigger a scale-up of one task for the service.
Solution 1:
I’m not sure how exactly it would work. When there are no healthy ALB targets the ALB returns 503 error, hence your visitors would see an error page instead of your website. That may trigger a Fargate container start but that often takes tens of seconds, sometimes even over a minute. By the time your container is up your visitor is probably gone.
If you want a truly serverless website with zero idle costs you’ll have to implement it using API.
- Put your frontend files (HTML, CSS, JS) in S3
- Load your dynamic content through API
- Implement the dynamic functionality in Lambda functions
- Use API gateway to call the Lambdas
- The DB can be Aurora Serverless or DynamoDB On-Demand
This architecture costs nothing when idle and provides instant response to your visitors.
Update: if you still want to scale down the Fargate Service to 0 Tasks you can certainly do it through setting the Service's DesiredCount to 0. That can be done e.g. through aws-cli:
~ $ aws ecs update-service ... --service xyz --desired-count 0
If you want to do this in Dev I suggest you run this UpdateService either manually, or from a cron-job, or from a scheduled Lambda function. Either way you can set the task to 0 at night and back to 1 the next working day. That'll be easier than relying on AutoScaling which may not be that reliable for very low traffic.
Hope that helps :)
Solution 2:
If re-writing your app to fit the above response it's not an option or costly, you could look into GCP CloudRun
CloudRun it's serverless containers developed by GCP. You can pack your website in a container and then CloudRun only bills you per CPU usage during requests and boot-up. It even has a really good free tier that will make running your app at minimum costs.
So you could combine Amazon Aurora with GCP CloudRun for minimum costs and no need to rewrite your app.