NGINX + HHVM + CI

Generally, the biggest problem you'll run into with running CodeIgniter in an environment like that is that you'll have a harder time finding people who can help with configuration issues. Also, you may want to look a little deeper into the framework tests to make sure CI passes. The URL and commit hash they have listed for CI are pretty old, but that might not mean anything.

Bonfire

Practical CodeIgniter 3
CodeIgniter Testing Guide