feat: Add DNS Registrar design decision

[osterman]

what

• Added a new design decision document for choosing where to register domains
• Presents two options: AWS Route 53 Registrar (recommended) and existing registrars (GoDaddy, Squarespace, Cloudflare, MarkMonitor)
• Includes detailed considerations: Cloudflare limitations, enterprise registrar options, Terraform support constraints, and legal implications
• Cross-linked with related design decisions (Vanity Domains and Service Discovery Domain)

why

• Consolidates domain registration guidance that was previously scattered across multiple documents
• Provides clear decision framework for reference architecture users choosing where to register domains
• Documents important limitations (e.g., Cloudflare apex NS delegation) and Terraform constraints (ClickOps required for registration)
• Enables practical domain strategy aligned with AWS-native DNS architecture

references

• Related to conversations about AWS Route 53 capabilities vs third-party registrars
• Clarifies Terraform provider limitations for domain registration (GitHub Issue #37670)

[trave-bloomerang]

This information makes sense. Is it fair to say that when electing to use AWS waiting on the core-dns account to be provisioned is a requirement?

[osterman]

This information makes sense. Is it fair to say that when electing to use AWS waiting on the core-dns account to be provisioned is a requirement?

Yes, exactly - provisioning core-dns is a requirement before proceeding. Additionally, using the AWS Route53 registrar requires a credit card added to the registrar, which is separate from your regular AWS billing. Will update the doc to note that as a consideration.