we (i and a colleague) have a system where we probe a large number of
IP addresses out there in the Internet. A probe consists of opening
a http URL on that system and when we get back the (expected) 401
response, we close the connection. about 7% of the time, we get no response
and we close the connection after several seconds.
for more or less any Intel-style server, we can run about 500-1000
probes per second (via a driver program with 50-100 threads).
here’s the unexpected part: we go to a cloud vendor and run this program
in a few instances, but no matter how many instances we run, once we get
to about 1000 probes/s total, additional instances or driving rates do not
increase the total rate, but simply increase packet loss and the number of calls
from the cloud vendor.
we’ve tried this on SIlverLining (an AT&T cloud) and RackSpace, with
pretty much identical results. we’ve hypothesized this as a limit of a site-wide
NAT box or some such, but it seems unlikely. before we go repeat this experiment
with other cloud vendors, does anyone have any comments on what this might be
or if other vendors might do better or worse?
andrew
-----------------------
Andrew Hume
949-707-1964 (VO and best)
732-420-0907 (NJ)
and...@research.att.com
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