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5.1.5.2. Configure Private DNS Zones

💡 First Principle: Private DNS zones provide secure, internal name resolution for resources within a virtual network, eliminating the need for custom DNS servers and preventing the exposure of internal network topology to the public internet.

Scenario: You have a web application in one Virtual Network that needs to communicate with a database in another Virtual Network using a custom private hostname like mydb.internal.local. You want to achieve this without deploying any custom DNS servers or exposing these internal names to the public internet.

What It Is: Azure Private DNS provides a reliable, secure DNS service for your virtual network.

Purpose:
Key Benefits:
  • Simplified Management: No DNS server VMs to deploy or maintain.
  • Automatic Registration: Azure VMs in linked VNets can auto-register their hostnames.
  • Split-Horizon DNS Elimination: Internal names resolve privately; public names resolve externally.
  • Enhanced Security: DNS queries and responses remain within Azure’s private network.
Configuration Steps (High-Level):
  1. Create a Private DNS zone.
  2. Link the DNS zone to one or more VNets via virtual network links.
  3. Enable auto-registration (optional).
Visual: Azure Private DNS Zone for Internal Resolution
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⚠️ Common Pitfall: Forgetting to link the Private DNS Zone to all VNets that require name resolution. A resource in an unlinked VNet will not be able to resolve names in the private zone.

Key Trade-Offs:
  • Managed Service (Private DNS) vs. Custom DNS Server: Private DNS is simpler and more integrated. A custom DNS server offers more control and can be used for complex hybrid scenarios but requires management and patching.

Reflection Question: How do Azure Private DNS zones, by providing internal name resolution for resources within linked VNets and supporting auto-registration, fundamentally simplify and secure internal DNS management by keeping all name resolution traffic within Azure’s private network?