[fix] MySQL cj jdbc CommunicationsException: Communications link failure

If you are working with Database in your app using ORM or Spring JDBC/Spring Boot JPA, you may get this exception,

Exception in thread "main" org.springframework.jdbc.CannotGetJdbcConnectionException: 
Failed to obtain JDBC Connection; nested exception is com.mysql.cj.jdbc.exceptions.CommunicationsException: 
Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. 
The driver has not received any packets from the server.

Caused by: com.mysql.cj.exceptions.CJCommunicationsException: Communications link failure

• Make sure your Database is up. Check connection to the database via DB Client or Console. Try doing telnet.
• How you defined the right database Hostname/IP Address in your JDBC DriverManager Connection URL?
• Have you defined the right Database server Port?
• Make sure your firewall settings are not restricting access.
• Make sure you have Internet connectivity.
• Make sure the Database server if having an IP Whitelisting policy, your IP is listed.
• If the Database Server is on Cloud (AWS/Azure/GCS), the right policies are set.
• If Database is on Docker Container, make sure the host port is exposed and accesiible