possibly cheaper on the cloud (Lambda vs EC2 instance)

Whoa, are you saying there's an autoscaler that doesn't use EC2 instances? I may be misunderstanding, but that would be very cool.

Maybe I should have said: my plan is to use AWS StepFunctions where a single task in the DAG is an entire ClearML pipeline . The non-ClearML steps would orchestrate putting messages into a queue, doing retry logic, and triggering said pipeline.

I think at some point, there has to be some amount of AWS-native architecture/infrastructure in order to react to objects landing in an S3 bucket in an event-driven way.