[openstack-dev] [Nova][Heat] scheduled-images blueprint

Mark Washenberger mark.washenberger at markwash.net
Thu May 2 15:20:03 UTC 2013


> > This is a workflow (not orchestration) feature and would be solidly
> in-scope for a WFaaS API (e.g. the proposed
> https://wiki.openstack.org/wiki/Convection mentioned several times in
> this thread) in the form of a much more generic "cloud cron" type feature.
>

Tangentially related, but I just want to get out ahead of the usage of
"cron" to describe this type of feature. I think its a bit of a hazard to
expose a cron-like interface for clouds, because cron gives the job
submitter too much control over the scheduling of their action. This
results in problems where a majority of users just pick the default time,
or midnight, or 4 AM, which causes strange load spikes in the underlying
system.

A better alternative is to express a frequency for the action only, (say
1/day, 1/week, 1/hour, whatever). You can still implement this interface as
a cron-like schedule under the covers. But now schedules can be initially
randomized, and a cloud administrator can take action if needed to
redistribute load.
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