newbie: can I have 2 A records?

[Nate Duehr]

On Thu, Apr 05, 2001 at 11:31:53AM +0800, Lik wrote:
> Can I have 2 A records as in:
> 
>      xserver    A     172.18.2.200
>      xserver    A     172.18.2.201

Yes, although depending on what DNS server you're running and what
version (assuming BIND 8.2.3-REL) different things will happen.

Generally that will cause folks to "round-robin" between the two IP
addresses when asking for "xserver", however this is not always the
case, and there's an excellent article written about why this is NOT a
good way to do load-balancing because of a few reasons.  The reasons (as
I understand them are):

- Different versions of server (including BIND, NT, and others) all vary
  on the way they answer requests for a name with multiple A-records.
- Different resolvers handle those (different) responses differently.

:-)  

Neat, eh?

The article is linked from one of the DNS resource sites linked from
the isc.org site -- I forget where -- anyone have it handy?

Don't expect a perfect 50%/50% split in traffic between the servers if
you do this.  It won't happen.  If it's an internal network with
perfectly heterogenous resolvers hitting it, you will be able to just
about predict the behavior, but if they're on the Internet, you won't.

If you need TRUE load-balanced behaviour, you have to buy a load
balancer that can deal with whatever type of traffic you're trying to
load-balance.

Hope it helps,
-- 
Nate Duehr <nate at natetech.com>

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