Ephemeral Applications are simply built in a manner that helps for maintainability. This is also known as “serverless” and immutable, although in reality all terms are misleading.
Fundamentally, an Ephemeral Application is easier to maintain and sustain because it is entirely configured at launch, and it has no state that it must maintain between restarting. This makes the entire process easier to own, and containers are a big part of making this happen.
To better understand this, you can reference The Factors of an Ephemeral App