Hi Dina,

Thanks for note about Climate logic.  This is something that will be very 
useful, when we will have to schedule from Nova multiple instances (of 
potentially different flavors) as a single request.  If the Solver Scheduler, 
can make a request to the Climate service to reserve the resources soon after 
the placement decision has been made, then the nova provisioning logic can 
handle the resource provisioning using the climate reserved leases.  Regarding 
Solver Scheduler for your reference, just sent another email about this with 
some pointers about it.  Otherwise this is the blueprint - 
https://blueprints.launchpad.net/nova/+spec/solver-scheduler
I guess this is something to explore more and see how Nova provisioning logic 
to work with Climate leases. Or this is something that already works.  I need 
to find out more about Climate.

Thanks,
Yathi.


On 2/11/14, 7:44 AM, "Dina Belova" 
<dbel...@mirantis.com<mailto:dbel...@mirantis.com>> wrote:

Like a restaurant reservation, it would "claim" the resources for use by 
someone at a later date.  That way nobody else can use them.
That way the scheduler would be responsible for determining where the resource 
should be allocated from, and getting a reservation for that resource.  It 
would not have anything to do with actually instantiating the 
instance/volume/etc.

Although I'm quite new to topic of Solver Scheduler, it seems to me that in 
that case you need to look on Climate project. It aims to provide resource 
reservation to OS clouds (and by resource I mean here instance/compute 
host/volume/etc.)

And Climate logic is like: create lease - get resources from common pool - do 
smth with them when lease start time will come.

I'll say one more time - I'm not really common with this discussion, but it 
looks like Climate might help here.

Thanks
Dina


On Tue, Feb 11, 2014 at 7:09 PM, Chris Friesen 
<chris.frie...@windriver.com<mailto:chris.frie...@windriver.com>> wrote:
On 02/11/2014 03:21 AM, Khanh-Toan Tran wrote:
Second, there is nothing wrong with booting the instances (or
instantiating other
resources) as separate commands as long as we support some kind of
reservation token.

I'm not sure what reservation token would do, is it some kind of informing
the scheduler that the resources would not be initiated until later ?

Like a restaurant reservation, it would "claim" the resources for use by 
someone at a later date.  That way nobody else can use them.

That way the scheduler would be responsible for determining where the resource 
should be allocated from, and getting a reservation for that resource.  It 
would not have anything to do with actually instantiating the 
instance/volume/etc.


Let's consider a following example:

A user wants to create 2 VMs, a small one with 20 GB RAM, and a big one
with 40 GB RAM in a datacenter consisted of 2 hosts: one with 50 GB RAM
left, and another with 30 GB RAM left, using Filter Scheduler's default
RamWeigher.

If we pass the demand as two commands, there is a chance that the small VM
arrives first. RamWeigher will put it in the 50 GB RAM host, which will be
reduced to 30 GB RAM. Then, when the big VM request arrives, there will be
no space left to host it. As a result, the whole demand is failed.

Now if we can pass the two VMs in a command, SolverScheduler can put their
constraints all together into one big LP as follow (x_uv = 1 if VM u is
hosted in host v, 0 if not):

Yes.  So what I'm suggesting is that we schedule the two VMs as one call to the 
SolverScheduler.  The scheduler then gets reservations for the necessary 
resources and returns them to the caller.  This would be sort of like the 
existing Claim object in nova/compute/claims.py but generalized somewhat to 
other resources as well.

The caller could then boot each instance separately (passing the appropriate 
reservation/claim along with the boot request).  Because the caller has a 
reservation the core code would know it doesn't need to schedule or allocate 
resources, that's already been done.

The advantage of this is that the scheduling and resource allocation is done 
separately from the instantiation.  The instantiation API could remain 
basically as-is except for supporting an optional reservation token.


That responses to your first point, too. If we don't mind that some VMs
are placed and some are not (e.g. they belong to different apps), then
it's OK to pass them to the scheduler without Instance Group. However, if
the VMs are together (belong to an app), then we have to put them into an
Instance Group.

When I think of an "Instance Group", I think of 
"https://blueprints.launchpad.net/nova/+spec/instance-group-api-extension";.   
Fundamentally Instance Groups" describes a runtime relationship between 
different instances.

The scheduler doesn't necessarily care about a runtime relationship, it's just 
trying to allocate resources efficiently.

In the above example, there is no need for those two instances to necessarily 
be part of an Instance Group--we just want to schedule them both at the same 
time to give the scheduler a better chance of fitting them both.

More generally, the more instances I want to start up the more beneficial it 
can be to pass them all to the scheduler at once in order to give the scheduler 
more information.  Those instances could be parts of completely independent 
Instance Groups, or not part of an Instance Group at all...the scheduler can 
still do a better job if it has more information to work with.


Chris

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--

Best regards,

Dina Belova

Software Engineer

Mirantis Inc.
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