Geographic load balancing with DNS

[Sven Ingebrigt Ulland]

On Tue, May 09, 2006 at 07:29:24PM +0200, Hans wrote:
> Who has experience with geographic load balancing with dns ?

I don't, other than in theory.

> What I am searching for is products and which databases there are available
> to map IP addresses to country's.

Have a look at
http://wiki.powerdns.com/projects/trac/browser/trunk/pdns/pdns/docs/gslb-operations.sgml?rev=2
for some ideas and challenges that you might face. (I am not affiliated
with PowerDNS in any way, and do not advocate for or against it.)

One of the main problems with mapping IP addresses to countries, is
that you only know the IP address of the client's local recursor,
which is not necessarily close to the client itself [1].

What you want to achieve is probably to have clients connect to
servers or sites that are geographically close to them, to reduce
latency. What you might also consider, is to take time zones into
account. For example, on day-time in Tokyo, the Tokyo server may be
flooded by "local" connections. You may then use some clever tricks to
redirect some of the requests to idle sites/servers, maybe in Europe
or America.

In any case, you probably need a dynamical back-end to serve requests.
BIND-DLZ (bundled with BIND 9.4?) or PowerDNS offer such features. You
might want to check them out.

On a sidenote, Akamai uses a mixture of DNS and a BGP backend, where
BGP route path lengths are incorporated into the DNS servers, to be
able to select a close server for a requesting client. [2]

regards,
Sven

[1] Anees Shaikh, Renu Tewari, and Mukesh Agrawal. On the
effectiveness of dns-based server selection. In Proc. of IEEE INFOCOM
2001, Anchorage, AK 2001.

[2] J. Dilley, B. Maggs, J. Parikh, H. Prokop, R. Sitaraman, and B.
Weihl.  Globally distributed content delivery. IEEE Internet
Computing, 6(7):50.  58, 2002.