Default region is more harmful than helpful

[cdegroot]

I just lost a couple of hours debugging an issue with a new environment where our Elixir code crashed with a permission error but the equivalent AWS CLI command on a shell ran just fine. This was an EC2 box in us-east-2 using an instance role.

It took me a while to realize that ExAWS has a default region when nothing is set, us-east-1. That explained why a different account (in us-east-1) ran the code just fine.

Consider removing that default, please. I think it's not the first time that a colleague or I got tricked by it, although today was one of the times that it took quite a while to realize that this was at hand. "us-east-1" is not a special region (anymore), and it is much more helpful to just crash when developers forget to explicitly configure a region either VM-wide or for a request. If we must have a default region, then probably the equivalent of {:system, "AWS_REGION"} is better than a hardcoded region.

(I am filing this as an issue to see whether people agree; I am, of course, more than happy to follow up with a PR if maintainers respond positively).