We are new to Oracle Cloud Infrastructure (OCI) and need to design our network for a three-tier web application, requiring strict security. What is the recommended strategy for configuring a Virtual Cloud Network (VCN), including subnets (public/private), Route Tables, and Security Lists? Specifically, how do OCI's Network Security Groups (NSG) differ from Security Lists, and which should be prioritized for granular control and a strong cloud security posture? We need to ensure we follow best practices to prevent unauthorized access
3 answers
The recommended OCI design pattern involves using regional VCNs with separate availability domain (AD) subnets for resilience. You should use private subnets for your application and database tiers, only using a public subnet for load balancers or bastion hosts. Prioritize using Network Security Groups (NSGs) over Security Lists. Security Lists are applied at the subnet level, meaning every resource in that subnet gets the same rules. NSGs, however, are applied directly to the VNIC of an individual resource (like a Compute instance or Load Balancer), offering much finer-grained cloud security control. Use NSGs to define rules based on the role of the resource (e.g., "Web Server NSG," "Database NSG"), which simplifies firewall rule management and enhances your overall network security.
If we opt for NSGs for granular control, how does that impact troubleshooting network access issues? Is it harder to trace firewall rules when they are applied per VNIC instead of per subnet via Security Lists?
Always use separate private subnets for your database and application tiers. Leverage NSGs for fine-grained firewall rules applied directly to your Compute and DB systems, as this is the current best practice for robust cloud security in a multi-tier OCI deployment.
And don't forget to implement a NAT Gateway in your VCN! It’s essential for allowing resources in your private subnets to securely initiate outbound connections (like patching or external API calls) without exposing them to the public internet, which is a foundational aspect of secure network design.
Troubleshooting with NSGs is generally easier once you understand the grouping logic. Since the security rules are logically tied to the resource's role, you only check the specific NSG associated with that resource's VNIC. With Security Lists, you'd have to check the list applied to the whole subnet, which might have overly broad rules. The key to easy tracing is consistent naming conventions for your NSGs—for example, App-Tier-Web-NSG. This helps maintain a robust cloud security posture.