Comment 14 for bug 1544839

this looks like a case where the apache config needs adjusting as you said Julian. I'm not surprised rally is able to crush the devstack apache basic config when using session (creating session quickly).

This also may be a case of connections being held open longer than needed. The two places I would look is

* see if request pipelining is being used (not sure) with the sessions and the session objects are lingering around after it is no longer needed.

* the apache config can be tuned for rally when used at higher concurrency.