Domain IP address for www and non-www for Canonical URL

Question

To handle Canonical URL is it best practice to do a 301 redirect or better to have the same IP Address for both www and non www domain?

For example:

Canonical URL/domain wanted is http://example.com

Domain           | A Record
------------------------------------
example.com      | 192.0.2.34
www.example.com  | 192.0.2.34

I understand people may have a CNAME record for www (alias, given that CNAME is called Canonical Name); unsure if this is best practice compared to using the same IP address.

Or is this better.

Domain           | A Record
------------------------------------
example.com     | 192.0.2.34
*  www.example.com 301 redirect to example.com

Answer 1

The mechanisms you describe (A and CNAME records vs. 301 redirects) are part of two different protocols (DNS and HTTP). A and CNAME records have nothing to do with which site your HTTP server serves for different requests.

Let's look at two different DNS configurations:

Configuration 1 (CNAME record)

Host             | Type  | Data
-----------------+-------+-------------
example.com      | A     | 192.0.2.34
www.example.com  | CNAME | example.com

• nslookup example.com resolves to 192.0.2.34
• nslookup www.example.com resolves to 192.0.2.34

Configuration 2 (A records)

Host             | Type  | Data
-----------------+-------+-------------
example.com      | A     | 192.0.2.34
www.example.com  | A     | 192.0.2.34

• nslookup example.com resolves to 192.0.2.34
• nslookup www.example.com resolves to 192.0.2.34

In both cases your canonical domain and your www subdomain resolve to 192.0.2.34. However, the only thing your HTTP server will recognize is that it receives requests for both example.com and www.example.com on the same IP address. But it doesn't know whether you used A or CNAME records for that.

TL;DR

You have to use HTTP 301 redirects to enforce the canonical example.com in HTTP requests. But that has nothing to do with your DNS configuration.