PHP Warning: PHP Startup: Unable to load dynamic library ‘/usr/lib64/php/5.5/modules/libevent.so’ – /usr/lib64/php/5.5/modules/libevent.so: undefined symbol: php_sockets_le_socket in Unknown on line 0

Warnings like this are typically due to certain module load order dependencies and can be fixed by ensuring the dependant module loads after the required module. In this case I reordered the module loads by renaming /etc/php-5.5.d/libevent.ini to x-libevent.ini (sockets.ini would then load before it.)