1. Comparing Public, Private, and Hybrid Cloud
Computing Options
By Judith Hurwitz, Robin Bloor, Marcia Kaufman, and Fern Halper from Cloud
Computing For Dummies
Cloud computing comes in three forms: public clouds, private clouds, and hybrids
clouds. Depending on the type of data you're working with, you'll want to compare
public, private, and hybrid clouds in terms of the different levels of security and
management required.
Public Clouds
A public cloud is one in which the services and infrastructure are provided off-site over
the Internet. These clouds offer the greatest level of efficiency in shared resources;
however, they are also more vulnerable than private clouds. A public cloud is the
obvious choice when

2. Your standardized workload for applications is used by lots of people, such as email.
You need to test and develop application code.
You have SaaS (Software as a Service) applications from a vendor who has a
well-implemented security strategy.
You need incremental capacity (the ability to add computer capacity for peak
times).
You’re doing collaboration projects.
You’re doing an ad-hoc software development project using a Platform as a
Service (PaaS) offering cloud.
Many IT department executives are concerned about public cloud security and
reliability. Take extra time to ensure that you have security and governance issues well
planned, or the short-term cost savings could turn into a long-term nightmare.
Private Clouds
A private cloud is one in which the services and infrastructure are maintained on a
private network. These clouds offer the greatest level of security and control, but they
require the company to still purchase and maintain all the software and infrastructure,
which reduces the cost savings. A private cloud is the obvious choice when
Your business is your data and your applications. Therefore, control and security
are paramount.
Your business is part of an industry that must conform to strict security and data
privacy issues.
Your company is large enough to run a next generation cloud data center
efficiently and effectively on its own.
To complicate things, the lines between private and public clouds are blurring. For
example, some public cloud companies are now offering private versions of their public

3. clouds. Some companies that only offered private cloud technologies are now offering
public versions of those same capabilities.
Hybrid Clouds
A hybrid cloud includes a variety of public and private options with multiple providers. By
spreading things out over a hybrid cloud, you keep each aspect at your business in the
most efficient environment possible. The downside is that you have to keep track of
multiple different security platforms and ensure that all aspects of your business can
communicate with each other. Here are a couple of situations where a hybrid
environment is best.
Your company wants to use a SaaS application but is concerned about security.
Your SaaS vendor can create a private cloud just for your company inside their
firewall. They provide you with a virtual private network (VPN) for additional
security.
Your company offers services that are tailored for different vertical markets. You
can use a public cloud to interact with the clients but keep their data secured within
a private cloud.
The management requirements of cloud computing become much more complex when
you need to manage private, public, and traditional data centers all together. You'll need
to add capabilities for federating these environments.
http://thecloudtutorial.com/nistcloudcomputingdefinition.html
Types of cloud computing
Cloud computing is typically classified in two ways:
1. Location of the cloud computing
2. Type of services offered
Location of the cloud
Cloud computing is typically classified in the following three ways:
1. Public cloud: In Public cloud the computing infrastructure is hosted by the cloud vendor
at the vendor’s premises. The customer has no visibility and control over where the

4. computing infrastructure is hosted. The computing infrastructure is shared between any
organizations.
2. Private cloud: The computing infrastructure is dedicated to a particular organization and
not shared with other organizations. Some experts consider that private clouds are not
real examples of cloud computing. Private clouds are more expensive and more secure
when compared to public clouds.
Private clouds are of two types: On-premise private clouds and externally hosted
private clouds. Externally hosted private clouds are also exclusively used by one
organization, but are hosted by a third party specializing in cloud infrastructure.
Externally hosted private clouds are cheaper than On-premise private clouds.
3. Hybrid cloud Organizations may host critical applications on private clouds and
applications with relatively less security concerns on the public cloud. The usage of both
private and public clouds together is called hybrid cloud. A related term is Cloud
Bursting. In Cloud bursting organization use their own computing infrastructure for
normal usage, but access the cloud using services like Salesforce cloud computing for
high/peak load requirements. This ensures that a sudden increase in computing
requirement is handled gracefully.
4. Community cloud involves sharing of computing infrastructure in between
organizations of the same community. For example all Government organizations within
the state of California may share computing infrastructure on the cloud to manage data
related to citizens residing in California.
Classification based upon service provided
Based upon the services offered, clouds are classified in the following ways:
1. Infrastructure as a service (IaaS) involves offering hardware related services using the
principles of cloud computing. These could include some kind of storage services
(database or disk storage) or virtual servers. Leading vendors that provide Infrastructure
as a service are Amazon EC2, Amazon S3,Rackspace Cloud Servers and Flexiscale.
2. Platform as a Service (PaaS) involves offering a development platform on the cloud.
Platforms provided by different vendors are typically not compatible. Typical players in
PaaS are Google’s Application Engine, Microsofts Azure,
Salesforce.com’s force.com .

5. 3. Software as a service (SaaS) includes a complete software offering on the cloud. Users
can access a software application hosted by the cloud vendor on pay-per-use basis.
This is a well-established sector. The pioneer in this field has been Salesforce.coms
offering in the online Customer Relationship Management (CRM) space. Other
examples are online email providers like Googles gmail and Microsofts hotmail, Google
docs and Microsofts online version of office called BPOS (Business Productivity Online
Standard Suite).
The above classification is well accepted in the industry. David Linthicum describes a more
granular classification on the basis of service provided. These are listed below:
1. Storage-as-a-service
2. Database-as-a-service
3. Information-as-a-service
4. Process-as-a-service
5. Application-as-a-service
6. Platform-as-a-service
7. Integration-as-a-service
8. Security-as-a-service
9. Management/Governance-as-a-service
10. Testing-as-a-service
11. Infrastructure-as-a-service