We want to move away from HHVM, as T176370 states; this task is the tracking task of the second quarterly goal for the SRE team work for switching to PHP7.

The goals we want to achieve are listed below, and a specific subtask will be created for each.

1. Allow directing users to PHP7 based on a cookie/header/beta feature
2. Separate Traffic layer caches for PHP7/HHVM
3. Evaluate scalability and performance of PHP7 compared to HHVM
4. Package and install PHP 7.2 in production in place of PHP 7.0
5. Assist in the production deployment of excimer (cf T205059), the new PHP7 profiler