What are Private Zones?

Private zones enable you to configure different DNS responses based on the originating Virtual Private Cloud (VPC) network of a DNS query for the same record. Think of it as a split-horizon DNS implementation, delivering tailored DNS information depending on where the request originates.

In essence, private zones allow you to have internal DNS records that are only accessible within your specified VPC network, while the public DNS records remain unaffected. This is extremely useful for managing internal services and infrastructure.

Here's a breakdown of the key concepts:

• Split Horizon DNS: The core principle behind private zones. It involves providing different DNS answers to clients depending on their network location. This allows you to use the same domain name for both internal and external resources.

• VPC Network Authorization: You explicitly authorize specific VPC networks to access a private zone. Only VMs within these authorized networks will receive the "private" DNS answers. Queries from outside these networks will not see the private zone's records.

• Same Record, Different Response: The beauty of private zones is that you can have the same DNS record (e.g., my-service.example.com) resolving to different IP addresses depending on whether the query comes from inside or outside your authorized VPC network.

Use Cases for Private Zones:

• Internal Service Discovery: Expose internal services (e.g., databases, internal web applications) only to your internal infrastructure without making them publicly accessible.

• Staging Environments: Configure separate DNS records for your staging environment, accessible only to developers and testers within a specific VPC.

• Hybrid Cloud Environments: When integrating on-premises infrastructure with cloud resources, private zones facilitate seamless name resolution across both environments.

Example Scenario:

Let's say you have an application named api.example.com.

• Public DNS: The public DNS record for api.example.com points to a public IP address, allowing external users to access your application.

• Private Zone: You create a private zone also for example.com and configure a record for api.example.com to point to an internal IP address within your VPC. Only VMs within the authorized VPC will resolve api.example.com to the internal IP, allowing them to communicate directly with the internal API service. External users will continue to resolve api.example.com to the public IP.

By using private zones, you improve security by isolating internal services, simplify internal networking, and manage different environments effectively.