https://docs.cloud.oracle.com/en-us/iaas/Content/Database/Tasks/migrating.htm Migration Connectivity Options You have several connectivity options when migrating your on-premises databases to the Oracle Cloud Infrastructure. The options are listed below in order of preference.
FastConnect: Provides a secure connection between your existing network and your virtual cloud network (VCN) over a private physical network instead of the internet. For more information, see FastConnect.
IPSec VPN: Provides a secure connection between a dynamic routing gateway (DRG) and customer-premise equipment (CPE), consisting of multiple IPSec tunnels. The IPSec connection is one of the components forming a site-to-site VPN between a VCN and your on-premises network. For more information, see VPN Connect.
Internet gateway: Provides a path for network traffic between your VCN and the internet. For more information, see Internet Gateway.

https://docs.cloud.oracle.com/en-us/iaas/Content/Database/Tasks/updatingDB.htm OS Updates Before you update the OS, review the following important guidelines and information:
Back up your DB system's databases prior to attempting an OS update.
Do not remove packages from a DB system. However, you might have to remove custom RPMs (packages that were installed after the system was provisioned) for the update to complete successfully.
Warning
Do not install NetworkManager on the DB system. Installing this package and rebooting the system results in severe loss of access to the system.
Oracle recommends that you test any updates thoroughly before updating a production system.
The image used to launch a DB system is updated regularly with the necessary patches. After you launch a DB system, you are responsible for applying the required OS security updates published through the Oracle public YUM server.
To apply OS updates, the DB system's VCN must be configured to allow access to the YUM repository. For more information

https://docs.cloud.oracle.com/en-us/iaas/Content/Database/Tasks/creatingDBsystem.htm