Database not working after upgrading to 8.1 from 7.9

[pkhoshroo]

Cannot create PoolableConnectionFactory (Communications link failure)

That means Ignition never even got to submit any username, as the database isn’t listening. If the DB is on a separate machine, you need to configure MySQL to listen to more than just localhost. After you fix that, you will certainly need to ensure Ignition is using a user name and password that exists in your database.

Make sure to follow the steps above and it is better to create another user login and try again if you haven't done that already.