I recently wrote up a lot about this:

https://convox.com/blog/ecs-challenges/

TL:dr it works very well. It's very flexible. But Amazon is still very hard for a lot of reasons.

One piece of data to share is that with ECS we are effortlessly running hundreds of production clusters and thousands of test clusters.

I'm not sure we could do this if ECS didn't exist.

ECS is incredibly powerful but definitely a lower-level primitive. We look at it sort of like a Kubernetes that we don't have to run for ourselves.

Scale has been great. We have customers running hundreds of containers on a single app without breaking a sweat.