We're in the planning phases of implementing an Amazon cluster for a
particular workflow.  We think volume will be such that it will make
sense to have at least a the manager and a worker node running working
all of the time and will be albe to reduce costs by using the reserved
instance pricing.  However, we have some questions about how auto
scaling works with regards to stopping vs. terminating worker nodes.
In my brief experience working with CloudMan I've been able to
determine that allocating instances that use EBS volumes accrues
charges.  With the 15GB EBS volume currently allocated by the CloudMan
AMI, starting a new worker node costs $1.50.  So if I start a worker
node, terminate it and start another one I get charged $3.00.
However, if I start an instance, stop it and restart it I only get
charged $1.50 for the initial allocation and I do not get charged for
restarting it.  Also, to my understanding (help me if I'm wrong here
because my experience is limited) I don't get charged for the time
where the volume is still mounted on EBS, but the instance is not
running.  I have a few questions regarding this.

1) For those with more experience with Amazon's pricing, is my scenario correct?
2) Will the autoscaling of nodes terminate unused nodes or simply stop them?
3) If autoscaling terminates nodes, is it possible to stop and restart
nodes within the cluster and not terminate them and still have
CloudMan utilize them in the cluster appropriately?


Jesse Erdmann
Bioinformatics Analyst
Masonic Cancer Center
University of Minnesota
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