Tuesday, October 11, 2011

Creating a Virtual Machine on/off schedule

“Wouldn’t it be nice to have a schedule to automatically turn VMs on or off at certain times of the day?” I’ve heard this from many of our clients, and this is definitely an interesting optimization problem.  Since most providers price by VM hours, one always needs to make sure not to end up with VM sprawl.  The fact that licensing on these VMs are also priced by the hour doesn’t help either.  So, yeah VM scheduling would be great but where do we start?

Actually, it isn't very complicated because most of us use load balancers anyway.  The load balancers are monitoring VM utilization (through connection count) and can thus keep track of times when all the VMs are underutilized.  Dr. Zarifoglu, in his load balancing article, identified thresholds for turning VMs on or off based on the workload.  So, turning one or more VMs off is simply an additional step after load balancing!

This leads to two possible approaches for VM Scheduling:
Dynamic scheduling – where VMs are automatically turned on or off based on demand and threshold policies, or
Static scheduling – where one would simply monitor VM utilization over time and come up with a user defined schedule that doesn’t change.

Obviously, the best approach would be to have a hybrid solution where the static schedule is automatically modified at fixed time intervals (say weekly) and is executed only after being approved by an administrator.  See Gravitant’s CloudMatrix – Policy Manager for more details on managing VMs in the cloud.


The caveat is that most cloud providers don’t allow simply turning VMs on or off (except for OpSource and Terremark).  Most providers will charge for stopped VMs as well, unless the VM is ‘deleted’.  So, an alternate process for turning a VM off (with the expectation of turning it on again at some point in time in the future) is to first create an image of the VM and save it in the backup storage space, and then ‘delete’ the VM.  In order to turn this VM back on, a new VM needs to be created and then the image from backup storage needs to be installed on the new VM before it can become functional.


As a result, the process of turning VMs on or off may be not be time and cost efficient.  However, here are a few alternate ways to do this:
(1) Go with a cloud provider like OpSource that allows VMs to be turned on or off at the click of a button and doesn’t charge for VMs that are turned off. (Note that there is a small fee for storage space occupied by the VM).
(2) Go with a cloud provider like Terremark that doesn’t even price by VM.  However, they would still charge for the OS licensing and storage if the VM was turned on at any point in time during the month.
(3) Go with any cloud provider but subscribe to an automated backup and restore service. Gravitant expects to provide this capability in its CloudMatrix console in early 2012.

For more information, go to www.gravitant.com.

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