WARNING: In Ecto 2.X you should not reference Mix.Ecto because it is a private API: Preload fails to checkout connection from poolboy · Issue #1586 · elixir-ecto/ecto · GitHub
And in Ecto 3.X, while Mix.Ecto is now considered public (i.e. no longer has @moduledoc false), the ensure_started function has been removed. Off the top of my head I’m not sure what you should use instead (but maybe it is Mix.Task.run).
