3 Service Models of cloud environment:
Software as a Service: Often geared toward the end
user who needs access through a web browser or other
thin client interface, SaaS provides access to applications
hosted on a service provider’s cloud infrastructure.
A business can find just about any general office
application available via the SaaS model. Customer
relationship management (CRM), calendaring, e-mail
and human resources management are among
some of the more common applications delivered
as services from the cloud infrastructure.
For IT departments, IT service management, spam
filtering, intrusion prevention and other traditional
security software are among the application types
increasingly available via the SaaS model.
With SaaS, the user organization neither
owns the application nor the associated servers,
operating systems, storage, network or other IT
resources required for its support and delivery.
The applications essentially come as-is, with little
to no opportunity to tweak user preferences.
Because of this, the commitments between a
customer and service provider can be fairly weak,
and if one SaaS option doesn’t work out, moving to
another provider is an option for the enterprise.
SaaS evolved from application
service provider and managed services
technologies and is perhaps the best
known and most mature type of cloud
service available today. Small- and
medium-sized businesses, limited by
staff and budget constraints, often
find the most benefit in this model,
although organizations of any size will
find SaaS useful to some degree.
Note that one common misconception
of cloud computing is that SaaS
equals cloud — perhaps because of the
innumerable SaaS offerings being pitched
by cloud companies today. While SaaS can
be delivered over a cloud infrastructure,
it is not a cloud in and of itself.
Platform as a Service: Derived
from the SaaS model, PaaS caters to
developers’ needs. Rather than simply
delivering prepackaged applications
via the cloud infrastructure, as is the
case with SaaS, a PaaS provider offers
up the entire computing platform and
solutions stack needed for an application.
With PaaS, a company can deploy
acquired or custom applications without
incurring the associated upfront
provisioning and ongoing maintenance
and management costs of the underlying
infrastructure. The user organization
has application control, the caveat in
many cases being that the developers
must be comfortable with the PaaS
provider’s choices for programming
languages, interfaces, development
tools, database support and the like.
The types of PaaS offerings vary;
which option works best for a business
depends on its goals. For example, some
cloud companies offer a PaaS and SaaS
combo, providing organizations with
the ability to customize the packaged
application. Although being able to
tweak the application may make the
SaaS model more attractive, the catch
is that when combined with a PaaS
offering, SaaS becomes less portable.
The richest PaaS offerings enable
an organization to support the entire
application development lifecycle.
This means that the PaaS provider not only provides the
platform itself but also ensures source code and version
control, enables user testing (with rollbacks as needed)
and provides change-tracking functions. PaaS can also
facilitate collaboration among far-flung developers.
Infrastructure as a Service: This service model enables
user organizations to forgo deployment of new data
center equipment to handle growing operational needs.
Rather, the business obtains needed IT infrastructure —
servers, security, storage, networks, etc. — from a cloud
services provider, often via a self-service catalog.
While a user company can run applications, databases,
operating systems and other software on top of its selected
infrastructure, it has no direct control over or access to
those machines. The cloud service provider manages the
infrastructure, including any scaling up or down as needed.
Infrastructure as a service is similar in concept to a
traditional dedicated hosting service, with two major
differences: Organizations tap into a shared, highly scalable
pool of resources, and they pay for only what’s used on a utility
basis. In other words, organizations neither have to preorder
nor pay for dedicated gear sitting in an outsourced data center.
IT shops must keep in mind, however, that multitenancy
applies across the public cloud infrastructure. They have no
way of controlling the types of virtual resources running
atop the infrastructure they’ve provisioned from the cloud.
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