IdeaWell

Project ideas from Hacker News discussions.

What came first: the CNAME or the A record?

Original Article

Hacker News Discussion

📝 Discussion Summary (Click to expand)

Based on the Hacker News discussion, here are the three most prevalent themes:

1. Interpretation and Ambiguity of DNS RFCs

The community is deeply divided on whether Cloudflare's change was a legitimate interpretation of the DNS standard or a breaking violation of an implicit contract. While Cloudflare argued that the RFC's wording was ambiguous due to the lack of modern normative language (MUST/SHOULD), many commenters found the requirement for CNAMEs to appear first to be explicit and clear.

  • Cloudflare's Justification: > "While 'possibly preface' can be interpreted as a requirement for CNAME records to appear before everything else, it does not use normative key words, such as MUST and SHOULD that modern RFCs use to express requirements." — paulddraper
  • Counter-Argument (RFC Clarity): > "It's pretty clear that CNAME is at the beginning. The 'possibly' does not refer to the order but rather to the presence. If they are present, they are are first." — paulddraper

2. Inadequate Testing and Regression Failures

A dominant sentiment is that Cloudflare failed to perform sufficient integration testing, specifically failing to test against the widely used glibc resolver. Commenters expressed shock that a change affecting global DNS infrastructure could be deployed without catching regressions that would have been evident in a standard test environment.

  • Critique of Testing Process: > "How is getaddrinfo not called in any unit or system tests?" — bpt3
  • Observation on Deployment: > "It's pretty concerning that such a large organisation doesnt do any integration tests with their dns infrastructure" — mcfedr

3. The Viability and Danger of Postel’s Law

The incident sparked a broad debate on "Postel’s Law" (be liberal in what you accept, conservative in what you send). Many argued that this principle is increasingly harmful in modern systems because it allows broken implementations to proliferate. The discussion favored "failing fast" over attempting to be compatible with ambiguous or malformed data.

  • Modern Rejection of the Law: > "Postel's law is considered more and more harmful as the industry evolved." — mmastrac
  • The Argument for Strictness: > "Warnings are ignored. It's much better to fail fast." — psnehanshu > > "The modern view seems to be you should just immediately abort if the spec isn't being complied with since it's possibly someone trying to exploit the system with malformed data." — Gigachad

🚀 Project Ideas

DNS Record Order Validator & Visualizer

Summary

  • [A tool that validates DNS response packet ordering against both historical behavior and RFC interpretations, highlighting potential breaking changes.]
  • [Core value: Prevents "Cloudflare-style" outages by simulating how different DNS clients will interpret and parse responses before deployment.]

Details

Key Value
Target Audience DNS provider engineers, SREs, and DevOps teams managing authoritative DNS servers.
Core Feature Packet-level DNS response validator that compares output against known client implementations (glibc, systemd-resolved, Cisco IOS, etc.) and flags ordering dependencies.
Tech Stack Rust/Go (for packet parsing), Python (for test orchestration), Docker (for environment isolation), Wireshark/tshark (for packet analysis).
Difficulty Medium
Monetization Revenue-ready: SaaS subscription for CI/CD integration, or on-premise enterprise license for large DNS providers.

Notes

  • [HN commenters like "paulddraper" and "Dylan16807" highlighted the RFC ambiguity, but also expressed frustration that "Cloudflare didn't have comprehensive integration tests." This tool bridges that gap by testing against real-world client behavior, not just spec compliance.]
  • [Addresses the unmet need for "comprehensive byte-by-byte test suite" mentioned by "skywhopper" and the lack of glibc testing noted by "ibejoeb".]

RFC "Ambiguity Detector" & Parser

Summary

  • [A static analysis tool that scans IETF RFCs and Internet Drafts to flag ambiguous language (non-normative terms like "possibly," "may," "should") and suggests normative alternatives (MUST, SHOULD, MUST NOT).]
  • [Core value: Prevents implementation divergence by identifying specification weaknesses before they become production issues.]

Details

Key Value
Target Audience Protocol designers, standards body contributors, and software engineers implementing RFCs.
Core Feature NLP-based scanner that highlights vague phrasing in RFC drafts, suggests RFC 2119-compliant language, and visualizes potential interpretation forks.
Tech Stack Python (NLP libraries like spaCy or NLTK), LLMs (for context-aware suggestions), Markdown/XML parsing for RFC formats.
Difficulty Medium
Monetization Revenue-ready: Freemium model for open-source contributors, paid enterprise features for large standards organizations (IETF, W3C).

Notes

  • [Directly addresses "hdjrudni" and "ShroudedNight"'s complaints about RFC ambiguity and the lack of normative language in older specs.]
  • [Potential for discussion: Could be integrated into IETF's Datatracker workflow to enforce stricter language during draft reviews.]

Resilient DNS Client Fuzzer

Summary

  • [A fuzzing tool that tests DNS clients against malformed or edge-case DNS responses to identify parsing bugs, order dependencies, and RFC non-compliance.]
  • [Core value: Catches issues like the glibc getaddrinfo bug before deployment, simulating "Hyrum's Law" scenarios where client behavior diverges from specs.]

Details

Key Value
Target Audience Developers of DNS libraries (glibc, musl, systemd-resolved), network security teams, and QA engineers.
Core Feature Generates randomized DNS responses with varying CNAME/A record orderings, NXDOMAINs, and SERVFAILs; monitors client crashes or incorrect parsing.
Tech Stack Rust (for performance and memory safety), libFuzzer/AFL++, DNS packet generation libraries (e.g., dnslib).
Difficulty High
Monetization Hobby (open-source) OR Revenue-ready: Consulting services for integrating into CI pipelines of large organizations.

Notes

  • [Reflects "kayson"'s and "jrochkind1"'s sentiment that tests should have caught the issue earlier; targets the "no tests asserting behavior remains consistent" gap.]
  • [Practical utility: Could have prevented the Cloudflare incident by testing glibc against reordered CNAMEs.]

DNS Versioning & Compatibility Layer

Summary

  • [A proxy/layer that sits between DNS resolvers and clients, normalizing responses based on detected client capabilities (e.g., reordering CNAMEs for glibc, preserving order for systemd-resolved).]
  • [Core value: Allows DNS providers to innovate (e.g., performance optimizations) without breaking legacy clients, acting as a "compatibility shield."]

Details

Key Value
Target Audience Large DNS providers (like Cloudflare, Google DNS) and enterprise network admins managing heterogeneous environments.
Core Feature Client fingerprinting (via EDNS, OS detection) and dynamic response transformation to match client expectations without violating RFCs.
Tech Stack Go or C (for low-latency packet modification), eBPF (for kernel-level traffic interception), Redis (for caching client profiles).
Difficulty High
Monetization Revenue-ready: Embedded in DNS provider infrastructure as a premium feature, or sold as a standalone appliance for enterprise networks.

Notes

  • [Aligns with "forinti"'s conclusion: "require CNAME records to appear in-order before any other records" is a pragmatic fix, but this tool allows flexibility without breaking compatibility.]
  • [Addresses "hdjrudni"'s point about warnings being ignored by providing a transparent fix instead of relying on client updates.]

Read Later