For anyone in the future with this problem, it was a problem in my Repo.init/2
It was overriding the :url variable with a system variable that was undefined.
Apparently if you use Ecto as a standalone it generates repo code that automatically overrides :url with a system variable making the :url setting useless unless the code is removed.
This was patched in phoenix where it checks if the system variable exists before overriding, but not in ecto…
