Today, there is a wide spectrum of services available in the cloud, including messaging solutions, collaborative solutions, identity management solutions, storage solutions, customer relationship management, and many more. Major vendors have also released cloud services based on their widely used on-premises software products. For example, Microsoft has released Office 365, which provides an online version of SharePoint Server, Exchange Server, and Lync Server. Microsoft also provides the Windows Azure platform, which makes the Windows Server operating system and other features available as services.
Notice how the Windows operating system (which the Azure Platform offers) and Microsoft Office server and client products (which Office 365 offers) are fundamentally different. An operating system provides a core set of functionality (hence the term platform) and what actually sits on top of it can be practically anything—from an e-commerce website to complex video processing software.
However, products such as Microsoft Exchange, which is a messaging solution, provide a welldefined set of features that target specific needs. This leads to an important observation: The number of ways and degrees to which a service is consumed and utilized can vary broadly. To address this in the world of cloud computing there are three different approaches to cloud-based services:
➤➤ Infrastructure as a Service (IaaS)
➤➤ Platform as a Service (PaaS)
➤➤ Software as a Service (SaaS)
Infrastructure as a Service (IaaS)
With Infrastructure as a Service (IaaS), you can basically outsource typical elements of infrastructure like virtualization, storage, networking, load balancers and so on, to a vendor of choice. The vendor offering IaaS bills you for the infrastructure services usage as per its service level agreement (SLA). One of the biggest benefits of IaaS is that it provides granular control, in which you can choose the core components for your infrastructure. With the launch of the VM Role on Azure, Microsoft has entered into the IaaS space along with vendors such as Amazon EC2, GoGrid, and OpSource, which already are key players in the IaaS market.
Platform as a Service (PaaS)
Platform as a Service (PasS) provides a core platform from which custom applications can deploy. With PaaS, you don’t have to work with infrastructure level elements and low level configuration of networking, security, and load balancers; all this is done for you by the vendor. The vendor provides you with a fully functional operating system with major platform software. For example, the Microsoft Azure platform provides support for the latest version of the .NET framework. This type of service offering means you can focus on deploying your custom applications on the platform and can easily configure your applications to scale up or down as demands change.
One of the key advantages of PaaS is that you don’t have to worry about performing operating system or application platform updates (for example, service packs) and hardware upgrades. The vendor regularly patches your operating system, whatever platform features are being offered (such as the core .NET platform or SQL database engine) and updates hardware on demand to meet your needs. Microsoft offers the Azure platform as a PaaS because it supports various types of Worker Roles and different types of applications. For example, you can run web applications with the Web Role, as well as host middle tier applications, such as Workflow, in the Worker Role. Similarly, SQL Azure provides Microsoft’s core relational database engine as a platform service.
Software as a Service (SaaS)
With Software as a Service (SaaS), the vendor manages everything from infrastructure, including load balancers and firewalls, to platforms, such as operating systems and virtual runtime environments like .NET and Java, all the way up to a complete line of business applications and services, such as e‑mail or a Customer Relationship Management product. SaaS provides you with fully provisioned and finished services with a well-defined feature set, which you can potentially later customize to a certain degree. Vendors usually provide browser-based interfaces so users can easily access and customize these services. APIs are also usually made available for developers. Microsoft Office 365 also offers these types of services, which currently include SharePoint Online, Exchange Online, Lync Online, and Office Professional Plus. Most of these online services have subset of the features of their on-premises counterparts.