How to size our servers for many zones hosting ?

[Simon Waters]

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Aktarus73 wrote:
>
> My company plan to host many primary zones (up to 500) with
Linux/Bind9.
> How should we size our server for supporting so many zones ?
> Are there any calculation rules to determine memory
consumption average for
> 100, 200, etc. zones ?

Assuming straight IPv4 authoritative server on the Internet with
no DNSSEC or exciting stuff, I saw just over 100 bytes per
record last time I looked. So allow yourself 300 bytes per
record, probably 5 or 6Kb per zone is more than enough for
typical web hosting. Obviously there are some chunky one time
overheads in Linux and BIND 9 before you add on the 10MB or so I
suspect you'll need for data.

Zone isn't a good measure as the average zone will depend on how
many NS servers, how many MX records per domain, and whether you
 have any zones which are more than just; SOA, NS, MX, and a
handful of A records. DNSRBL lists for example can be huge, last
one I looked at swallowed 17MB of RAM when loaded, and it was
only one of a set, the others were larger.

Thus authoritative DNS can often be handled by quite a small
box, but hey most x86 memory is cheap (DNS servers are redundant
because you deploy several in different places, right? So no
need for fancy fault tolerant hardware if not using dynamic DNS).

I routinely fill up all the memory slots when buying x86 boxes
as it is cheaper to do this when buying than to take the time
out to upgrade later when a later bloated OS release appears
(which they usually do eventually). Okay memory will be cheaper
and bigger in 3 years time, but can you justify the time and
expense (and risk) of opening an operational box in 3 years time
just to save 100 or 200 USD today. (Well maybe if you are a
small operation).

If you are providing recursive lookup as well (hopefully not on
the same box) then memory is more likely to be an issue.
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