DNS Basics

Question

What is DNS and how does the DNS resolution process work step by step?

Answer

DNS (Domain Name System) translates human-readable domain names to IP addresses. Resolution flow: browser cache → OS cache → resolver (ISP/configured DNS) → root servers → TLD servers → authoritative nameservers. Common record types: A (IPv4), AAAA (IPv6), CNAME (alias), MX (mail), TXT (verification).

Why This Matters

DNS is fundamental to how the internet works. DevOps engineers need to understand DNS for configuring domains, troubleshooting connectivity issues, setting up load balancers, managing SSL certificates, and configuring email services.

Code Examples

DNS troubleshooting commands

bash

Local DNS configuration

bash

Common Mistakes

Forgetting about DNS caching when making changes (TTL)
Using CNAME at the apex/root domain (not allowed)
Not understanding DNS propagation delays

Follow-up Questions

Interviewers often ask these as follow-up questions

What's the difference between A records and CNAME records?
What is TTL and why does it matter?
How would you set up DNS for a load-balanced application?