To connect an application hosted in Oracle Cloud Infrastructure (OCI) to a database located on-premises (on your own data center or a different network), you can use various methods depending on your network architecture and security requirements. Here are some common approaches:

1. Oracle Cloud VPN or FastConnect:

Oracle VPN: You can set up a VPN (Virtual Private Network) connection between your OCI Virtual Cloud Network (VCN) and your on-premises network. This allows your application in OCI to access resources on-premises securely as if they were in the same network.

Oracle FastConnect: Oracle FastConnect provides a dedicated, private connection between your on-premises network and OCI. It offers higher bandwidth and lower latency compared to VPN connections. This method is suitable for high-performance applications.

Once you've established the network connectivity, you can configure your OCI resources (compute instances, database instances, etc.) to use the private IP addresses within your on-premises network.

2. VPN Solutions:

If you have your own VPN infrastructure (such as an IPSec VPN) in place, you can establish a VPN tunnel between OCI and your on-premises network. This typically involves configuring VPN gateways on both sides to facilitate secure communication

3. Public IP and Security Rules:

If your on-premises database is exposed to the public internet (not recommended for sensitive data), you can use its public IP address to connect from OCI. Ensure that you configure appropriate security rules to allow traffic from OCI IP addresses to your database's public IP

4. Oracle Cloud NAT Gateway

If you don't want to expose your on-premises database to the public internet, you can use an Oracle Cloud NAT (Network Address Translation) Gateway to allow your OCI resources to initiate outbound connections to your on-premises network securely.

5. Oracle Cloud Bastion

You can set up an Oracle Cloud Bastion host within your VCN. This Bastion host can be used as a secure jump host to access resources on-premises. It provides an additional layer of security by requiring SSH authentication to access the Bastion host before connecting to on-premises resources.

6. Database Gateway:

If you're connecting to a non-Oracle database on-premises, you might need to use Oracle Database Gateway for ODBC (or another relevant gateway) to enable connectivity between Oracle Cloud applications and the non-Oracle database.

The specific method you choose depends on factors such as security requirements, performance needs, and your existing network infrastructure. It's crucial to consult with your network and security teams and follow best practices for network connectivity and security.

Additionally, Oracle provides detailed documentation and support for setting up network connections between OCI and on-premises environments. Be sure to refer to Oracle's official documentation and consider engaging with Oracle support for assistance with your specific scenario.

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