[Fix] Spring Boot: mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure

2023-04-12T16:38:05.616-05:00 ERROR 74117 
--- [main] com.zaxxer.hikari.pool.HikariPool: HikariPool-1 - Exception during pool initialization.

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.
 at com.mysql.cj.jdbc.exceptions.SQLError.createCommunicationsException(SQLError.java:174)
 ~[mysql-connector-java-8.0.14.jar:8.0.14]

Caused by: com.mysql.cj.exceptions.CJCommunicationsException: Communications link failure
Caused by: java.net.SocketTimeoutException: Connect timed out
Caused by: org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection

Process finished with exit code 1

If you are getting the above exception stack trace in your Spring Boot application, below are some reasons for this issue and ways to fix the issue,

• Make sure that the MySQL database server is running. If it's a remote server check with your DBA or DevOps team if the service is up.
• Try doing telnet/ping from your system to see if the MySQL server is reachable
• Check that you have provided the correct server hostname in the configuration in the Spring Boot project application.properties file.
• Make sure the JDBC driver is corret
• If you have connection pool set up say HikariCP, ensure that the pool configuration is correct
• Check if there is no firewall rule that is blocking access.
• Try restarting the MySQL server and Spring Boot application.