This was originally posted as a twitter thread: https://twitter.com/chrisachard/status/1188870256971915265

Confused by DNS Records? A, CNAME, ALIAS...

Me too 😬

Let's change that! (cheatsheet at the end)

🔥 DNS Record crash course for web developers 👇

1.

To get to www.example.com, your computer needs to know where on the Internet that server is

That means: it has to know what IP address to talk to

The way it finds out is the Domain Name System (DNS)

2.

When you register a domain, you can set many types of DNS Records

Each record has a Type, a Host, and a Value

• "Types" are predefined
• "Host" represents the root (@) or a subdomain (www)
• "Value" is an IP or web address, or other value

3.

The A record maps a subdomain to an IPv4 address

This is most commonly used at the root, so it tells your browser where example.com lives

The AAAA record does the same for IPv6

4.

CNAME maps a subdomain to another domain name

This can be another subdomain on the same site (like forwarding www to the root)

or another domain like heroku - where your app lives

5.

But there's a problem with CNAME!

Once you define a CNAME record for a subdomain (host), you CAN'T DEFINE another record for that same subdomain

Because of this, you can't use CNAME at the root level (where you need other records to exist)

6.

To fix that, ALIAS is used (sometimes ANAME)

ALIAS is like CNAME, but it's a non-standard dns type

So you can use ALIAS to forward your root domain (example.com) to your app's server (example.herokudns.com)

7.

That lets you put other records at the root, like:

TXT records, which provide extra info to any computer reading the DNS record

TXT records are often used to prove you own a domain - because only the domain owner can set a DNS record.

8.

Or:

MX records (Mail eXchange), which you use to specify another server that handles your email (like google)

MX records are unique because you can set multiple servers that are each given a "priority"

9.

There are many other record types, but those are the ones you'll most often set yourself.

For each record, you also specify a Time To Live (TTL)

This tells DNS servers how long to cache your DNS values

10.

TTL is why it can take some time for your new domain records to "propagate"

DNS servers, your ISP, and even your own computer can cache DNS records, serving up the "old" values until the TTL runs out

Cheatsheet

Hopefully that made DNS a bit less confusing for when you set up your next domain!

To put it all together, here's a PDF cheatsheet of this crash course: https://chrisachard.com/cheatsheets/dns-cheatsheet.pdf

🎉

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