I think you're missing some aspects of cattle. You're still supposed to keep track of what happens and where. You still want to understand why and how each of the servers in the autoscaling group (or similar) behaves. The cattle part just means they're unified and quickly replaceable. Buy they still need to be well tagged, accounted for in planning, removed when they don't fulfil the purpose anymore, identified for billing, etc.
And also importantly: you want to make sure you have a good enough description for them that you can say "terraform/cloudformation/ansible: make sure those are running" - without having to find them on the list and do it manually.
And also importantly: you want to make sure you have a good enough description for them that you can say "terraform/cloudformation/ansible: make sure those are running" - without having to find them on the list and do it manually.