Why Even Cloudflare Struggles with DNS: The Deceptively Complex Foundation of the Internet

#dns #webdev

The Deceptive Simplicity of DNS

One of the foundational components at Cloudflare is DNS. As one of the largest enterprises in the software industry, managing over 20% of the world's internet traffic, Cloudflare has built its reputation for security, CDN services, and other products on its DNS expertise.

Yet even they experience DNS issues. DNS problems are one of the worst nightmares technical teams face because they cascade across infrastructure like nothing else.

If Cloudflare, with all their expertise, has DNS problems, what does that tell us?

Is DNS Simple? Yes and No.

What is DNS? The Domain Name System is a hierarchical and distributed naming service that provides a naming system for computers, services, and other resources on the internet.

Basically, anything with an IP address can get a domain name. Those domain names usually point to IPs via DNS records.

DNS records live in authoritative DNS servers such as Google's 8.8.8.8, Cloudflare's 1.1.1.1, and others.

When you visit example.com, your device first checks the browser cache and the local DNS cache. If no record is found, it follows your network configuration to locate an authoritative name server to query. After reaching the resolver (your network’s recursive DNS server), the resolver contacts three servers in sequence.

First is the root server, which stores information about TLDs like .io and .com and identifies which TLD server is responsible for each. Next, the TLD server directs the resolver to the authoritative name server for the specific domain. That authoritative server contains the DNS records you’ve configured. Once retrieved, the result is returned to your browser and cached for future use.

Fun fact: DNS is the most heavily queried database system in the world.

DNS servers achieve their speed by storing DNS records in zone files, which are structured text files loaded directly into RAM for extremely fast access.

The "This is Simple" Illusion: Simple Surface, Infinite Depth

Most people add a few records, run some queries, see things working, and think they've mastered DNS. But that's just the tip of the iceberg. As mentioned earlier, one of the hardest problems you'll encounter in software is almost always related to DNS in some way.

Think of DNS as your home address. If no one knows that address, no one can reach you. But unlike a home address that you share with a few people, DNS is an address that needs to propagate to billions of devices worldwide once authoritative name servers get a record of it.

A single misconfiguration in DNS doesn't affect just one component—it cascades faster than almost any other system failure.

This rapid propagation is fundamental to how DNS was designed. You're putting a DNS record in to have a name pointing to the resource you're trying to make accessible to other resources or people, and that usually happens in milliseconds. Even though you sometimes see "changes take 48 hours to appear," the speed is a feature, not a bug. But it means mistakes spread just as quickly as corrections.

Common DNS Problems That Keep Engineers Up at Night

1. TTL (Time To Live) Misconfiguration

Imagine setting a TTL of 86400 seconds (24 hours) on a critical record, then needing to change it urgently. You're now stuck waiting up to 24 hours for this change to fully propagate because caching servers worldwide will hold onto the old value. The cache will only invalidate once the TTL of your previous record expires.

2. CNAME Chain Loops

You create a CNAME record pointing to another domain, which points to another, which accidentally points back to the first. Suddenly DNS resolvers enter an infinite loop. Queries fail, and your entire service becomes unreachable. These chains can be hard to spot in large infrastructures with multiple teams managing different zones.

3. Split-Horizon DNS Conflicts

Your internal DNS says api.example.com points to 10.0.0.5, but your external DNS says it points to 52.123.45.67. An employee working remotely suddenly can't access the internal service because their VPN isn't routing DNS queries correctly. Debugging takes hours because the problem appears and disappears based on network location.

4. DNSSEC Validation Failures

You enable DNSSEC for security, but a key rotation goes wrong or a signature expires. Now, instead of your site being accessible but potentially vulnerable, it's completely unreachable for anyone with DNSSEC validation enabled, with cryptic error messages that don't mention DNS at all.

5. Propagation Delays and Race Conditions

You update a DNS record and immediately deploy new infrastructure to that address. Some users get the new record instantly, while others are still seeing the cached old record for minutes or hours.

The DNS Learning Simulation: A Lesson in Humility

One interesting project I worked on with an intern involved creating a mini DNS simulation. We had fun, but the real purpose was teaching a lesson for both of us : we will never know everything. Our brain isn't designed to store complete knowledge about any complex system. We have limited cognitive capacity, and our best approach is to know just enough to get the job done effectively and know where to reference information when you need to refresh your memory.

This principle holds true even for proclaimed experts in their fields. Take C++ as an example. The language comes with multiple standardizations—C++98, C++11, C++14, C++17, C++20, C++23—each with hundreds of features, edge cases, and gotchas. If someone claims they know everything about C++, you can easily construct a scenario involving template metaprogramming, undefined behavior, or obscure standard library details that will humble them quickly.

DNS is no different. The tip of the iceberg is genuinely simple—point a name to an IP address. But once you decide to dive deeper, there's no end. It's like a decision tree where every node branches into multiple paths, and each path leads to more branches.

Consider this example: You start investigating why a query is slow. That leads you to examine authoritative nameservers, which leads to TTL settings, which leads to caching behavior across multiple resolver layers, which leads to anycast routing, which leads to BGP configurations, which leads to geographic DNS policies, which leads to EDNS client subnet considerations, which leads to privacy implications, which leads to DNS-over-HTTPS versus DNS-over-TLS debates, which leads to studying Certificate Authority Authorization records, which leads back to DNSSEC... and before you arrive at the depth you were searching for, you've probably forgotten which root node your investigation began at. Was it the slow query? The failed health check? The intermittent timeout?

The Missing Tool: Why We Need a DNS Simulator

The best way to truly understand DNS complexity would be through a comprehensive DNS simulator. To my surprise, no such tool exists in production quality. In the current software engineering industry, even at the biggest companies with the best engineers, when they make DNS changes, it's at most an educated guess backed by experience and prayer.

They run staging environments, yes. They have monitoring, absolutely. But they can't truly simulate how a DNS change will propagate across thousands of recursive resolvers with different caching policies, how it will interact with CDN configurations, how mobile devices switching between networks will handle it, or how edge cases in specific resolver implementations will respond.

This tool would need to model:

Multiple recursive resolver behaviors (Google DNS, Cloudflare DNS, OpenDNS, ISP resolvers)
Caching layers at different TTL stages
DNSSEC validation chains
Anycast routing scenarios
Network partition simulations
DNS cache poisoning attempts
Rate limiting behaviors
EDNS extensions and compatibility

Building this will take significant time—likely months of dedicated development to even reach a minimally viable prototype. But it's on my 2026 calendar because the industry desperately needs it. Every day, engineers at companies large and small make DNS changes hoping they won't cause the next cascading failures. A proper simulator could transform DNS operations from educated guessing into confident engineering, done via a simulation.

The Reality of DNS in Production

DNS combines several challenging aspects of distributed systems:

Global scope: Your changes affect the entire internet
Caching complexity: Multiple layers with independent policies
No rollback mechanism: Once propagated, you can't easily undo a DNS change
Debugging difficulty: Problems manifest differently based on location, resolver, and timing
Security implications: DNS is a frequent attack vector (DDoS amplification, cache poisoning, subdomain takeovers)

Even Cloudflare, with their massive infrastructure and DNS expertise, has experienced outages traced back to DNS issues.

The lesson here isn't that DNS is impossible to master. It's that treating it as "simple" is the fastest path to production incidents. Respect its complexity, document your configurations meticulously, make changes conservatively, and always have a rollback plan (even if it means waiting out a TTL period).

Until we have better simulation tools, DNS operations will remain part science, part art, and part crossing your fingers.