You may see this error in your agent logs.
This article is for our v1 agent and will soon be deprecated.
main - ERROR - getMySQLStatus: MySQL connection error: (2002, "Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)")
As per the MySQL documentation this "normally means that there is no MySQL server running on the system or that you are using an incorrect Unix socket file name or TCP/IP port number when trying to connect to the server. You should also check that the TCP/IP port you are using has not been blocked by a firewall or port blocking service."
One solution describes how to change the permissions of the sock file so that this will work properly.