Module 4

Module 4: DNS Reliability and Performance

⏱ 6–8 hours

The systems that keep DNS working when everything else is on fire. Caching, anycast, monitoring, DR, and the post-mortems you should have read before your last outage.

Module 4: DNS Reliability and Performance

DNS is not glamorous infrastructure. It's not the part people put on their resumes. It's the part that, when it works, nobody notices — and when it breaks, takes down everything from your API to your login page to your internal tooling.

This module is about making DNS boring again, in the best sense: predictable, observable, and recoverable.

What You'll Cover

By the time you finish Module 4, you'll have a working model for how DNS behaves under load, how to design for failure, and how to actually debug the thing instead of just restarting it and hoping.

Lessons

  1. DNS Caching Strategies and Optimizations — TTL is a dial, not a setting. Learn how to tune it for normal ops, planned changes, and active incidents.

  2. Anycast DNS: Improving Resilience and Performance — How Cloudflare, Route 53, and every serious DNS operator at scale routes queries to the nearest healthy node without clients knowing.

  3. DNS Monitoring and Logging Best Practices — What to actually put in your Grafana dashboard. Specific metrics, specific thresholds, specific alert conditions.

  4. Troubleshooting DNS Issues: Tools and Techniques — The full toolkit from dig +trace to tcpdump, with a methodology that starts at the root zone and works down.

  5. DNS Scalability: Handling High-Volume Traffic — What high-volume actually means, where the bottlenecks are, and why horizontal scaling of resolvers is easier than you think.

  6. Disaster Recovery and Business Continuity for DNS — What to do when your DNS provider goes down. Spoiler: if you don't have a secondary provider before the incident, you're not doing DR.

  7. DNS Performance Metrics and Benchmarking — How to measure resolution latency properly, what good looks like (P99 under 10ms), and how to use dnsperf before production finds out.

  8. Case Studies: DNS Failures and Lessons Learned — Dyn 2016. Facebook 2021. Cloudflare June 2022. And a small TTL misconfiguration that took down a migration for four hours.

Prerequisites

You should have completed Modules 1–3 or have equivalent working knowledge of DNS record types, zone structure, recursive and authoritative resolution, and DNSSEC basics.

A Note on Scope

This module focuses on the operational layer — what you do after the zone is configured and serving. The lens here is reliability and recovery. Some overlap with Module 3 in case studies, but security mitigation is not the focus.

The content is written for the engineer who owns DNS in production. Some of this will feel obvious in retrospect. That's fine. Post-mortem culture exists because obvious things still go wrong.

Module 4 of 6 in the DNS Masterclass by Anouar Adlani.