Starting today with the release of dnspython==2.0.0, using pymongo in a flask app running with gunicorn with eventlet workers breaks when using a hostname for the Mongo DB instead of an IP. I have not had time to investigate this issue in-depth, but pinning dnspython<2 works as expected. I will see if I can add some more info later.

cc @Trolldemorted @mauricesvp @MMunier (for updates in this issue)