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From Madan Ganesh Velayudham <>
Subject Re: [PROPOSAL] Introduce API returning you an answer from CloudStack storage/host allocators whethere there is enough resources for vm deployment
Date Sat, 01 Feb 2014 02:20:55 GMT
Makes lot of sense. Would the same API allow the caller just to check (not actually proceed
to create) whether resources are present for a particular payload? This may be useful for
the client who want to proactively check and avoid returning failure. 

Are there any race condition possibilities when multiple requests are received?

Madan Ganesh Velayudham P.M.P, C.S.M.,

On 01-Feb-2014, at 5:56 am, Alena Prokharchyk <> wrote:

> Currently there is no way to know if there is enough resources for vm deployment, before
actual deployVm call is made. The sequence is the following:
> 1) Deploy Vm is called
> 2) DB record is created for the Vm
> 3) Storage/Host allocators determine whethere there are enough resources for vm to be
deployed, and return deploy destination to the caller stack.
> 4) If allocator returns valid deploy destination, VM gets actually created/started on
the backend. If allocators don't return the destination, the DB record created on step 2)
gets destroyed, and ResourceAllocation exception is thrown back to the API caller.
> The API I'm going to introduce, would help you to determine whether CS physical resources
- hosts, storages - can potentially accomodate vm deployment (considering template/service/diskOffering)
at a given time, w/o actually calling the deploy vm. Some admins might find this call useful
as they can always make this check before submitting the deployVm, so in case it returns NO,
you can fail the deployment immediately, w/o calling deployVm. Also you can make this call
to determine what is lacking for certain vm deployment, and expand your physical resources
> Please let me know if see any pitfalls in the proposal, as well if you see any other
use cases that can be solved using this API.
> Prachi, can you please point me to an existing method (or interface) defined in Allocators
code serving this purpose?
> Thanks,
> -Alena.

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