Magellan Final Report - Office of Science - U.S. Department of Energy

Chapter 2
Background
The term “cloud computing” covers a range of delivery and service models. The common characteristic
of these service models is an emphasis on pay-as-you-go and elasticity, the ability to quickly expand and
collapse the utilized service as demand requires. Thus new approaches to distributed computing and data
analysis have also emerged in conjunction with the growth of cloud computing. These include models like
MapReduce and scalable key-value stores like Big Table [11].
Cloud computing technologies and service models are attractive to scientific computing users due to the
ability to get on-demand access to resources to replace or supplement existing systems, as well as the ability
to control the software environment. Scientific computing users and resource providers servicing these users
are considering the impact of these new models and technologies. In this section, we briefly describe the
cloud service models and technologies to provide some foundation for the discussion.
2.1 Service Models
Cloud offerings are typically categorized as Infrastructure as a Service (IaaS), Platform as a Service (PaaS),
and Software as a Service (SaaS). Each of these models can play a role in scientific computing.
The distinction between the service models is based on the layer at which the service is abstracted to the
end user (e.g., hardware, system software, etc.). The end user then has complete control over the software
stack above the abstracted level. Thus, in IaaS, a virtual machine or hardware is provided to the end user
and the user then controls the operating system and the entire software stack. We describe each of these
service models and visit existing examples in the commercial cloud space to understand their characteristics.
2.1.1 Infrastructure as a Service
In the Infrastructure as a Service provisioning model, an organization outsources equipment including storage,
hardware, servers, and networking components. The service provider owns the equipment and is responsible
for housing, running, and maintaining it. In the commercial space, the client typically pays on a per-use
basis for use of the equipment.
Amazon Web Services is the most widely used IaaS cloud computing platform today. Amazon provides
a number of different levels of computational power for different pricing. The primary methods for data
storage in Amazon EC2 are S3 and Elastic Block Storage (EBS). S3 is a highly scalable key-based storage
system that transparently handles fault tolerance and data integrity. EBS provides a virtual storage device
that can be associated with an elastic computing instance. S3 charges for space used per month, the volume
of data transferred, and the number of metadata operations (in allotments of 1000). EBS charges for data
stored per month. For both S3 and EBS, there is no charge for data transferred to and from EC2 within a
domain (e.g., the U.S. or Europe).
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