If you’re like me, you prefer to keep things updated as often as possible. Besides, keeping things updated is a part of preventing security breaches and taking advantage of bug fixes. Unfortunately, this can cause a headache with Magento 2.
Magento 2 fails to load and reports 1 exception(s):Exception #0 (Exception): Deprecated Functionality: Function mcrypt_module_open() is deprecated.
This isn’t really a fix but a work around. It appears the mcrypt extension has been deprecated in PHP 7.1. Unfortunately, it appears Magento 2 still utilizes functions derived from the extension. For the time being, you will need to revert to PHP 7.0.
If you would like to see any additional changes, check out the PHP 7.1 change log Here