Cloudware Vendor Solutions - Guide to Cloud Computing for Business and Technology Managers - page 333

3. The Spot Instances model enables consumers to bid for Amazon EC2
computing capacity. Spot price, which varies in real time based on
supply and demand. In case of spot instances, users bid on unused
capacity and their instances are launched when the market price
reaches the threshold specified by the user.
There are three pricing models for EC2 instances: on-demand, reserved, and
spot. On-demand instances use a flat hourly rate, and the user is charged
for the time an instance is running; no reservation is required for this most
popular model. For reserved instances, a user pays a one-time fee to lock in
a typically lower hourly rate. This model is advantageous when a user antici-
pates that the application will require a substantial number of CPU cycles,
and this amount is known in advance. Additional capacity is available at the
larger standard rate. In case of spot instances, users bid on unused capacity,
and their instances are launched when the market price reaches a threshold
specified by the user.
16.2 Platform as a Service (PaaS) Solutions
For many businesses, specific rather than general requirements may mean
that a generic SaaS application will not suffice. PaaS creates a managed envi-
ronment in the cloud where complex, tailor-made applications can be con-
structed, tested, and deployed. The provider supplies a hardware platform
together with software environments specifically designed to support cloud
application development. The target users are developers who build, test,
deploy, and tune applications on the cloud platform (for the end user, the
result is still a browser-based application). Automatic scalability, monitoring,
and load balancing are provided so that an increase in demand for a resource
such as a Web application will not result in degradation in performance (of
course, this may mean an increased charge is incurred). PaaS vendors will
also ensure the availability of applications, so, for example, should there be
any problems on the underlying hardware, the application will be automati-
cally redeployed to a working environment, without a detrimental effect on
the end user's experience. PaaS should accelerate development and deploy-
ment and result in a shorter time to market when compared with traditional
software development using an organization's own data center.
The developer does not control and has no responsibility for the underlying
cloud infrastructure but does have control over the deployed applications.
The vendor is responsible for all operational and maintenance aspects of the
service and will also provide billing and metering information. The vendor
commonly offers a range of tools and utilities to support the design, integra-
tion, testing, monitoring, and deployment of the application.