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Hectal
Phase 3Intermediate4 of 8 in Networking

DNS — The Internet's Phonebook

How a name becomes an address, every record type you'll use, TTLs and caching, debugging with dig, and DNS inside Docker, Kubernetes, and the cloud.

'It's always DNS' is a joke because it's so often true: expired records, wrong TTLs, split-horizon surprises, search domains, and resolver outages have caused some of the largest outages in internet history. This phase makes DNS predictable.

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4 topics ~28 min 5 code blocks & diagrams
Start with the first topic
1
3.1

How DNS Resolution Works

Your machine asks a recursive resolver, which walks the hierarchy from the root servers to the TLD servers to the domain's authoritative servers, caching each answer for its TTL.

7 min 1 diagram 1 code practice

2
3.2

DNS Record Types You'll Actually Use

A, AAAA, CNAME, ALIAS, MX, TXT, NS, SOA, SRV, CAA, and PTR each answer a different question; knowing which one to use avoids the classic apex-CNAME and email-verification mistakes.

7 min 1 code practice

3
3.3

Debugging DNS Like an SRE

Most DNS incidents come from a handful of causes (stale caches, wrong resolver, search-domain surprises, split horizon, NXDOMAIN caching); dig with the right flags finds them quickly.

7 min 1 code practice

4
3.4

DNS for Service Discovery: Docker, Kubernetes & the Cloud

Inside platforms, DNS is how services find each other: Docker's embedded resolver, CoreDNS in Kubernetes, Route 53 private zones, and health-checked records for failover.

7 min 1 code practice