DNS

Networking · Beginner · 4 min read

What is it?

DNS is the system that translates human-friendly domain names like example.com into the numeric IP addresses computers use to find each other.

Explain like I'm 5

DNS is like the internet's phone book: you know the name of who you want to reach, and DNS looks up their actual number for you.

Why was it created?

People can't remember strings of numbers for every site, so DNS was created to map memorable names to changing IP addresses.

Where is it used?

Resolving website domains
Routing email to mail servers
Service discovery in infrastructure
Load distribution across regions

Why should developers care?

DNS underlies every domain you visit. Misconfigured DNS is a common cause of outages developers must debug.

How does it work?

When you request a domain, your computer asks DNS resolvers, which walk a hierarchy of servers until they find the record mapping the name to an IP. Results are cached for a set time (TTL).

Real-world example

Visiting a site triggers a DNS lookup that returns its server's IP; your browser then connects to that address to load the page.

Common use cases

Pointing a domain at a server
Email delivery (MX records)
Verifying domain ownership (TXT records)
Geographic traffic routing

Advantages

Human-friendly names
Decouples names from changing IPs
Caching makes it fast
Globally distributed and resilient

Disadvantages

Caching means changes can take time to propagate
Misconfiguration causes hard-to-spot outages
Can be a target for attacks

When should you use it?

Whenever you publish a service under a domain name.

When should you avoid it?

You can't really avoid it for named services; you only choose how to manage it.

Alternatives

Connecting directly by IP address (impractical at scale)

Related terms

CDN Load Balancer Amazon Route 53 HTTP

Interview questions

Beginner

What does DNS do?
What is an A record?

Intermediate

What is TTL and how does it affect changes?
What is the difference between A and CNAME records?

Senior

How would you reduce DNS-related downtime during a migration?
How does DNS-based traffic routing work?

Common misconceptions

"DNS changes take effect instantly" — caching and TTLs can delay propagation.
"DNS stores website content" — it only maps names to addresses, not the pages themselves.

Fun facts

DNS stands for Domain Name System.
A record's TTL tells resolvers how long to cache it before checking again.

Timeline

1983 — DNS introduced to replace manual host files

Learning resources

MDN: What is DNS?

Quick summary

DNS is the internet's directory, turning domain names into the IP addresses computers use to connect.

Cheat sheet

Maps domain names to IPs
Hierarchical and cached (TTL)
A, CNAME, MX, TXT records
Changes take time to propagate

If you remember only one thing

DNS turns names you can remember into the IP addresses machines actually use.