This repository contains the PHP7 (currently 7.4) HTTP template, it uses RoadRunner RoadRunner to handle the interaction between the watchdog and that of the PHP function.
RoadRunner communicates with the PHP function utilising PSR-7 so your handler must return a PSR-7 response, it's also worth noting that if you echo or print that'll cause an error as that uses STDOUT - you'll want another debugging strategy.
This is not production ready, lots of testing is required. Note: Tweak RR workers and evaluate performance