You can use AWS Accounts like microservices. The biggest security walls in AWS are the account barriers. Those have to be specifically configured to cross. Sometimes (1%) its unavoidable, but if you have multiple services running on an account, you force yourself to weave arcane webs of IAM permissions crisscrossing all over to get what you need where. It's a terrible model that people inflict on themselves because it's how everything used to work.