CentOS/RHEL 7.X ship with MariaDB and not MySQL. Does anyone have MySQL running on a CentOS/RHEL 7.X? Did you run into any issues with dependencies/etc faced?
Note MySQL DB would be used for Ambari, HS2, Ranger and Oozie.
MariaDB should not be causing any issue (however it is unsupported). However the Databases that are listed here: http://docs.hortonworks.com/HDPDocuments/Ambari-188.8.131.52/bk_Installing_HDP_AMB/content/_database_req... are the Tested and certified configurations.
@Andrew Watson MySQL DB is a certified database and it should work ok on Centos/RHEL7.X when used as HDP Metastores. A future release would start supporting the default MariaDB which is shipped with these OS.