Information Technology Reference
In-Depth Information
Choosing Cloud Instances
Administrators can make a choice from among various levels of compute, memory, storage,
and networking instances. Some public cloud vendors, especially the ones offering PaaS and
IaaS models, offer certain types of instances at lower prices. For instance, Amazon EC2 offers
Spot Instances, which are spare instances that provide excess capacity at a lower price than
normal ones. You can find out more at the following locations:
https://aws.amazon.com/ec2/purchasing-options/spot-instances/
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-spot-instances.html
Amazon says that the customer simply bids on spare Amazon EC2 instances and runs
them whenever the bid exceeds the current Spot Price. The price for such instances fluctu-
ates periodically depending on supply and demand for Spot Instance capacity. For this to be
useful, however, business applications should have flexibility for when applications will run.
This is because the instance runs only when the customer's maximum price is greater than
the current Spot Price. If so, the instances will run and terminate only if one of the two con-
ditions is met: the customer terminates them or the Spot Price increases above the customer's
maximum price.
At the time of this writing, the potential savings for using Amazon Spot Instances against
Amazon Reserved Instances was between 200 and 800 percent per hour (
http://aws.amazon
.com/ec2/pricing/
). This statistic is for general-purpose instance types (medium, large, and
extra large) depending on utilization requirement (light, medium, and heavy). Moreover, Spot
Instances do not accompany any upfront costs.
Similarly, Rackspace offers a monthly rate for faster cloud block storage on a per-GB
basis, versus its cloud backup service. The potential savings for using the backup service
instead of block storage is around 120 percent. More information is available at the follow-
ing location:
www.rackspace.com/cloud/public-pricing/#cloud-block-storage
It is important to survey and spend time experimenting with the application in order
to determine the optimal level of compute, memory, and storage that is required. And it
is equally important to know which applications can be deployed on spare instances and
which cannot. For instance, Spot Instances make perfect candidates for daily batch process-
ing systems or as short-term storage for machine logs that need not be kept for long time
periods. An interesting use case will be to utilize spare instances for processing machine-
generated log data for regular maintenance tasks.
Balancing Required Service Levels
Each application has its own service-level profile: its general purpose and functions. For
example, a publically accessible e-commerce website will have a different level of service
requirements than an internal employee portal. Evaluating the costs of public cloud instances
against the service levels needed for various applications can help in optimizing the public
cloud costs.
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