[zard784]

Does it understand how to mutate resources in-place with out a downtime? Or is that code/logic something I need to write and track like I do today?

[lindydonna]

(Disclosure: I work at Pulumi)

Yes, Pulumi does mutate resources in place, if the cloud provider supports it. For most resources, it will create a new one (such as a new ECS task), and wait for it to be ready before deleting the old one.