On 04/03/2017 06:07 PM, Blair Bethwaite wrote:
Hi Jay,
On 4 April 2017 at 00:20, Jay Pipes <[email protected]> wrote:
However, implementing the above in any useful fashion requires that Blazar
be placed *above* Nova and essentially that the cloud operator turns off
access to Nova's POST /servers API call for regular users. Because if not,
the information that Blazar acts upon can be simply circumvented by any user
at any time.
That's something of an oversimplification. A reservation system
outside of Nova could manipulate Nova host-aggregates to "cordon off"
infrastructure from on-demand access (I believe Blazar already uses
this approach), and it's not much of a jump to imagine operators being
able to twiddle the available reserved capacity in a finite cloud so
that reserved capacity can be offered to the subset of users/projects
that need (or perhaps have paid for) it.
Sure, I'm following you up until here.
Such a reservation system would even be able to backfill capacity
between reservations. At the end of the reservation the system
cleans-up any remaining instances and preps for the next
reservation.
By "backfill capacity between reservations", do you mean consume
resources on the compute hosts that are "reserved" by this paying
customer at some date in the future? i.e. Spot instances that can be
killed off as necessary by the reservation system to free resources to
meet its reservation schedule?
The are a couple of problems with putting this outside of Nova though.
The main issue is that pre-emptible/spot type instances can't be
accommodated within the on-demand cloud capacity.
Correct. The reservation system needs complete control over a subset of
resource providers to be used for these spot instances. It would be like
a hotel reservation system being used for a motel where cars could
simply pull up to a room with a vacant sign outside the door. The
reservation system would never be able to work on accurate data unless
some part of the motel's rooms were carved out for reservation system to
use and cars to not pull up and take.
> You could have the
reservation system implementing this feature, but that would then put
other scheduling constraints on the cloud in order to be effective
(e.g., there would need to be automation changing the size of the
on-demand capacity so that the maximum pre-emptible capacity was
always available). The other issue (admittedly minor, but still a
consideration) is that it's another service - personally I'd love to
see Nova support these advanced use-cases directly.
Welcome to the world of microservices. :)
-jay
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