A MySQLAgent cannot connect to the MySQL instance. The full error message usually looks like this:
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server. com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
This is one of the most common errors and indicates that the DB isn't reachable with the connection properties provided.
This can have one or more of the following causes:
Each one can be tested with the corresponding number solution: