Explanation
To enable access to a compute node port, you enable the appropriate security rule. When you enable one of the predefined security rules, the given port on the compute node is opened to the public internet. To enable access to a different port, or restrict access to a port, you must create a security rule.
Note: When a database deployment is created, the following Oracle Compute Cloud Service security rules are created, but set to a disabled status.
References: References: Using Oracle Database Cloud Service (February 2017), page 3-7
https://docs.oracle.com/en/cloud/paas/database-dbaas-cloud/csdbi/using-oracle-database-cloud-service.pdf