How to receive only one sns notification triggered via autoscaling event.

This isn't possible currently, but I've passed on this feedback to the internal AutoScaling team. The only workaround currently would be to aggregate the notifications via EventBridge, and then create your own mechanism to trigger an SNS notification once a threshold is breached. Ex, :

• Have the Event notify Lambda which records the entries in a DB
• Have the Event logged in a CloudWatch log group; which has a metric filter to create a custom metric; link an alarm to that custom metric

https://docs.aws.amazon.com/autoscaling/ec2/userguide/cloud-watch-events.html