Cloud Computing - Cloud Data Management - page 15

2. Community cloud . The cloud infrastructure is shared by several organizations and
supports a specific community that has shared concerns (e.g., mission, security
requirements, policy, and compliance considerations).
3. Public cloud . The cloud infrastructure is made available to the general public or a
large industry group and is owned by an organization selling cloud services (e.g.
Amazon, Google, Microsoft). Since customer requirements of cloud services
are varying, service providers have to ensure that they can be flexible in their
service delivery. Therefore, the quality of the provided services is specified
using Service Level Agreement (SLA) which represents a contract between a
provider and a consumer that specifies consumer requirements and the provider's
commitment to them. Typically an SLA includes items such as uptime, privacy,
security and backup procedures. In practice, Public clouds offer several key
benefits to service consumers such as: including no initial capital investment on
infrastructure and shifting of risks to infrastructure providers. However, public
clouds lack fine-grained control over data, network and security settings, which
may hamper their effectiveness in many business scenarios.
4. Hybrid cloud . The cloud infrastructure is a composition of two or more clouds
(private, community, or public) that remain unique entities but are bound together
by standardized or proprietary technology that enables data and application
portability (e.g., cloud bursting for load-balancing between clouds). In particular,
cloud bursting is a technique used by hybrid clouds to provide additional
resources to private clouds on an as-needed basis. If the private cloud has the
processing power to handle its workloads, the hybrid cloud is not used. When
workloads exceed the private cloud's capacity, the hybrid cloud automatically
allocates additional resources to the private cloud. Therefore, Hybrid clouds offer
more flexibility than both public and private clouds. Specifically, they provide
tighter control and security over application data compared to public clouds,
while still facilitating on-demand service expansion and contraction. On the
down side, designing a hybrid cloud requires carefully determining the best split
between public and private cloud components.

Table 2.2 summarizes the four cloud deployment models in terms of ownership,
customership, location, and security.

2.5 Public Cloud Platforms: State-of-the-Art

Key players in public cloud computing domain including Amazon Web Services,
Microsoft Windows Azure, Google App Engine, Eucalyptus [ 16 ], and GoGrid
offer a variety of prepackaged services for monitoring, managing, and provisioning
resources. However, the techniques implemented in each of these clouds do vary.
For Amazon EC2, the three Amazon services, namely Amazon Elastic Load Bal-
ancer [ 5 ], Amazon Auto Scaling [ 2 ], and Amazon CloudWatch [ 3 ], together expose
functionalities which are required for undertaking provisioning of application