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Faut-il utiliser des CNAME pour les sous-domaines ?

ayi

I manage multiple websites that currently have le suivant DNS configuration:

example.com      - A Record - Production Server IP
test.example.com - A Record - Test Server IP
www.example.com  - CNAME    - example.com
beta.example.com - CNAME    - test.example.com
dev.example.com  - CNAME    - test.example.com

Is this an approprié use of CNAME records? J'ai looked online et have pas found a clear answer. Some people claim that CNAME records are bad (they are not, cependant, clear on why this is) et propose le suivant setup:

example.com      - A Record - Production Server IP
test.example.com - A Record - Test Server IP
www.example.com  - A Record - Production Server IP
beta.example.com - A Record - Test Server IP
dev.example.com  - A Record - Test Server IP

Which one of these is le better approach (and why)?

Note : The subdomains do pas require leur own MX records, so that is pas an issue here.

ayi

Yes, c'est an approprié use of CNAMEs. In le discussions J'ai been part of, le arguments tend to go like this:

Against CNAMEs:

Il y a a (tiny) performance penalty, as le downstream DNS caches need to perform 2 DNS lookups, one for le CNAME et one for le A-Record le CNAME points to.
Vague, bogus arguments about CNAMEs having less "authority" ou compatibility issues.

In favor of CNAMEs:

They provide a clean abstraction entre hardware (physical servers) et services.
They simplify DNS management -- quand a server moves, you seulement need to change one record.

After trying a couple of différent ways to do this, I now have a personal favorite style. It is:

I find that this setup works well. It keeps extra DNS lookups for le CNAMES down; et si a server crashes I can encore change public DNS around fairly fast.

Voici a (improvised) example in BIND syntax:

;name     ttl   class rr     value 
server01  30m   IN    A      192.168.0.3
server02  30m   IN    A      192.168.0.4

webmail   24h   IN    CNAME  server01
extranet  24h   IN    CNAME  server02
ftp       24h   IN    CNAME  server02