The library we are currently using to aggregate the Tuleap metrics is mostly abandoned and have some limitations (most notable one is that we can not pass our already initialized instance of a Redis client).
The library have been forked and some work has been done to fix existing bugs and transforming into something more fit for the PHP 7 era.
Goal is to tag/release the library and to use it in Tuleap.
https://github.com/Enalean/php-prometheus-client