Geographical Load Balancing
steve at bluehost.com
Thu Nov 12 09:11:54 MST 2009
On 11/11/2009 04:50 PM, Corey Edwards wrote:
> Ryan Byrd wrote:
>> having a super short TTL is a great way to overload your DNS servers and
>> clients don't have to honor the TTL anyway and will often cache the records.
>> IE caches records for 30 mins, I believe, for example.
> I will vouch for that fact. Even worse, Outlook Express will cache until
> it is shutdown.
> Another trick some setups use is to order DNS replies so that the
> primary/nearest/best is listed first and the secondary/farthest/worst
> follow. Well that's all well and good until it runs through another DNS
> server who is not bound to honor that ordering, and typically will not.
> Here are a few URLs I've bookmarked on the topic. HTH
Even many clients don't follow the order you give them. In fact,
windows (up through vista, don't know about 7) tend to have some broken
method of figuring out the response time of all of it's resolvers, and
then use the slowest, most overloaded of them. Truly annoying from a
server farm perspective.
And yes, 5 seconds TTLs do tend to pound on the servers more, but not
all that bad if the server is authoritative (ie, already has the zone
and doesn't have to go look for it) and has relatively current
hardware. My DNS servers are pushing about 1500 queries per second
(each) and have been tested to about 9000 per second.
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