commercial example of SaaS is Outlook.com, which is a messaging service on the
Internet. An enterprise example is Office 365 , which provides a cloud-hosted
Exchange, SharePoint, and Lync service, all accessed over the Internet with no
application or operating system management for the organization.
The first type of cloud solution, infrastructure as a service, differs from an on-
premises solution (where you are responsible for everything) because IaaS enables
your focus to shift to the components within a virtual machine. This is because IaaS
basically provides the ability to host virtual machines. You can see in Figure 12. 1 that
the IaaS provider is responsible for the networking, storage, server, and virtualization
layer, and then you are responsible for all aspects of the operating system within the
VM, the middleware, the runtime, data, and of course the application. While it may
seem like IaaS gives the most flexibility, the trade-off is that the amount of
management required is still high. Many organizations, however, may first dip their
toe into the cloud by using IaaS and then move on to the other types to cut down on
management and gain benefits offered with PaaS and SaaS.
Platform as a service drastically changes the amount of management for your
organization. With PaaS, you have to worry only about the application you manage
and the data, leaving everything else to the PaaS provider. I should point out that
although you manage the data, the provider likely still provides services to replicate
and protect the data.
Finally, with software as a service, you are responsible for nothing. You just use the
cloud-based software. Not every system can be SaaS, because some organizations have
their own custom code, but the goal for many organizations is a combination of PaaS
and IaaS, and there will always be some systems on premises.
Unless your organization enjoys IT infrastructure management, the end goal is SaaS
for everything. With SaaS, the complete service is provided, backed up, updated, and
maintained completely for you. Your only work is basic administration. However, only
certain types of solutions are available as SaaS. Popular examples include messaging,
collaboration, and customer relationship management. Even when a SaaS solution is
available, its flexibility may be limited because, remember, the vendor is providing
this service for thousands of customers on a shared infrastructure, which limits the
amount of customization possible. Therefore, even if a solution is available as SaaS, it
may not be a good fit for some organizations.
If a SaaS solution is not available, the next best choice is PaaS. With PaaS, you can
focus on just your application, provided you write the application in a language
supported by the PaaS offering and stay within its guidelines. The challenge for many
organizations is that they have legacy applications that don’t fit within the guidelines
and the developers have long since left the company, leaving no documentation and
no hope of making the application work in a PaaS environment. Additionally, many
organizations run applications by third parties who don’t follow the guidelines for the
application to run in PaaS. Although PaaS is a great solution, many applications are
therefore simply not a fit.