OT: Load Balancing & redundancy using Multiple A records

Julian Field MailScanner at ecs.soton.ac.uk
Fri Nov 23 15:59:07 GMT 2007

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shuttlebox wrote:
> On Nov 23, 2007 12:13 PM, Steve Freegard <steve.freegard at fsl.com> wrote:
>> It works, but don't expect it to load balance well.  For that you really
>> do need a proper load-balancer that can examine metrics of each of the
>> back-end systems and direct connections to them accordingly.
> I use this method both on the public (many-to-few) and the private
> side (few-to-few) of the network and it works real well. Over a months
> worth of traffic I see a difference of only 1-2%.
Join the club. I use round-robin DNS between a bunch of A records in my 
single MX record, and it load balances it long-term rather nicely. The 
web page you referred to talks all about the rules and regs but doesn't 
really take account of what is actually implemented. Yes, the rules say 
that DNS imposes no order in the results of a lookup. But in practice 
the implementers tend to just read in an array and use it in order. So 
it does help in my experience, whatever the rulebook says.

Just my 2p worth.


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Julian Field MEng CITP CEng
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