DNS Based Load Balancers

Lincoln Dale ltd at interlink.com.au
Wed Jul 5 09:18:55 UTC 2006

 >> but it's a perfect example of why GSLB based on DNS ain't perfect.
 > What would be a better solution then?

utopia would be for DNS to be enhanced in some manner such that the 'end
user ip-address' became visible in the DNS request.
utopia would have NAT devices which actually updated that in-place so an
authoritive nameserver always authoritively _knew_ the public ip-address of
where the request was coming from.

alas, we don't live in utopia and have to settle for alternate solutions.

one such approach is rely on protocol-specific mechanisms.  e.g. if its
HTTP, then something at HTTP.
oh wait - that won't deal with HTTP proxies either - but at least there is
some standardization on HTTP headers that proxies insert giving a hint of
the original client ip-address.

there are other approaches also.  a few years back when i spent a fair bit
of time in this area, my experience is that a hybrid system based on
"specific protocol" and "generic solution" (dns) worked best.  this simply
isn't an area where "one solution fits all cases".

there are public companies whose business model depends on this being 'hard'
to do right.  them being capable of doing something 'better' than not all
all is the reason they are still in business.
i did a fair bit of research in this area as part of work i used to do a few
years back.  much of that research belongs to my employer - i thought it was
documented publicly in the form of a patent i am a co-inventor of - but
alas, i can't seem to find it on uspto.gov .. perhaps it hasn't been issued
yet .. i haven't tracked these things for years.

in either case, i guess its an example of where even commercial entities
whose business model depends on 'getting it right' most of the time do
indeed 'get it wrong' also.



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