com.mysql.jdbc.Driver not loaded. Are you sure you've included the correct jdbc driver in :jdbc_driver_library

for logstash 6.2.x and above, prefer adding the drivers under:

/usr/share/logstash/logstash-core/lib/jars/

and rather keep the jdbc_driver_library empty. this has been quoted in many of the elastic.co forums too.

Logstash can't load the driver because it's looking for the driver in the wrong place, you should always specify the full path to a driver e.g.:

jdbc_driver_library => "/opt/drivers/mysql-connector-java-8.0.15.jar"