Doesn't seem possible to drop a database while MIX_ENV=prod

This is a postgres question not an ecto one. That error is postgres telling you that you cannot drop a db while other concurrent connections to the database exist. Stop those other connections and the drop should start working.

Though I’d argue that these kind of operations should generally not be done through mix commands in a production environment. Imo it’s better to use a limited user account with the application, preventing it doing any harmful operations on accident. One off tasks like deletion of a db then happen on the side using some admin credentials independently from the application.

I don’t know if this is the right way to do it but

MIX_EVN=prod mix ecto.rollback --all

…is a quite sufficient compromise for me (perhaps not even a compromise at all)