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From Mike Tutkowski <mike.tutkow...@solidfire.com>
Subject Question about selecting an EndPoint
Date Sat, 01 Feb 2014 07:02:48 GMT
Hi,

In the copyObject method of AncientDataMotionStrategy, we have the
following code to select an EndPoint:

            EndPoint ep = selector.select(srcForCopy, destData);

            if (ep == null) {

                String errMsg = "No remote endpoint to send command, check
if host or ssvm is down?";

                s_logger.error(errMsg);

                answer = new Answer(cmd, false, errMsg);

            } else {

                answer = ep.sendMessage(cmd);

            }
If you needed to know which EndPoint was going to be selected BEFORE this
copyObject method was invoked, how could one do that?

For example, I have a use case in 4.4 where I need to have CloudStack tell
the storage driver in use to create a volume on its storage system.
CloudStack then needs to tell the driver to grant hosts in a particular
cluster access to this volume. After this, CloudStack needs to tell the
hypervisor in use for the cluster to copy the template down to the recently
created storage (this is a case where we are spinning up a VM based on a
template that uses managed storage).

The way I was planning on doing this was to select an EndPoint using
similar logic to what's above and then pass that EndPoint in to both the
method that grants hosts access to the recently created volume AND pass
that same EndPoint in to the copyObject method (this necessitates creating
a new method on the interface that AncientDataMotionStrategy implements).

Thoughts on this? These are the steps in outline form:

* CloudStack wants to deploy a VM that uses a template to managed storage
(an example of managed storage is that the XenServer SR does not exist
before we kick off the VM...the SR (and the VDI that represents the
template) is created on the fly to house the root disk of the VM).

* CloudStack tells the storage driver in use to create a volume on its
storage system (this volume will be used for our XenServer SR).

* CloudStack tells the storage driver to grant hosts in the applicable
cluster access to the volume the driver just created (this is where we
first need to know of a host in the applicable cluster).

* CloudStack sends a command to a host in the applicable cluster to create
an SR based on the volume the driver just created, then the host downloads
a template to the SR.

Once this has completed, you now have a single template as a root disk on a
newly created SR. The volume the SR is on has guaranteed IOPS (Quality of
Service is the reason we want only a single template on the SR). When the
VM is expunged, its root disk (and the SR it was housed on) are destroyed.

Thanks!

-- 
*Mike Tutkowski*
*Senior CloudStack Developer, SolidFire Inc.*
e: mike.tutkowski@solidfire.com
o: 303.746.7302
Advancing the way the world uses the
cloud<http://solidfire.com/solution/overview/?video=play>
*(tm)*

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