[openstack-dev] [Tempest][Production] Tempest / the gate / real world load

Robert Collins robertc at robertcollins.net
Thu Dec 12 19:23:42 UTC 2013

A few times now we've run into patches for devstack-gate / devstack
that change default configuration to handle 'tempest load'.

For instance - https://review.openstack.org/61137 (Sorry Salvatore I'm
not picking on you really!)

So there appears to be a meme that the gate is particularly stressful
- a bad environment - and that real world situations have less load.

This could happen a few ways: (a) deployers might separate out
components more; (b) they might have faster machines; (c) they might
have less concurrent activity.

(a) - unlikely! Deployers will cram stuff together as much as they can
to save overheads. Big clouds will have components split out - yes,
but they will also have correspondingly more load to drive that split

(b) Perhaps, but not orders of magnitude faster, the clouds we run on
are running on fairly recent hardware, and by using big instances we
don't get crammed it with that many other tenants.

(c) Almost certainly not. Tempest currently does a maximum of four
concurrent requests. A small business cloud could easily have 5 or 6
people making concurrent requests from time to time, and bigger but
not huge clouds will certainly have that. Their /average/ rate of API
requests may be much lower, but when they point service orchestration
tools at it -- particularly tools that walk their dependencies in
parallel - load is going to be much much higher than what we generate
with Tempest.

tl;dr : if we need to change a config file setting in devstack-gate or
devstack *other than* setting up the specific scenario, think thrice -
should it be a production default and set in the relevant projects
default config setting.

Robert Collins <rbtcollins at hp.com>
Distinguished Technologist
HP Converged Cloud

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