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 👇
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)
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 (
- "Value" is an IP or web address, or other value
A record maps a subdomain to an IPv4 address
This is most commonly used at the root, so it tells your browser where
AAAA record does the same for IPv6
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
But there's a problem with
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)
To fix that,
ALIAS is used (sometimes
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 (
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.
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"
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
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
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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Thanks for reading!