- IaaS: A form of cloud computing that provides virtualized computing resources. You essentially use IaaS to replace physical resources, such as servers, with virtual resources hosted and managed by Amazon.
- SaaS: A software distribution service that lets you use applications without actually having the applications installed locally. Another term used to describe this service is software on demand. The host, Amazon, maintains the software, provides the required licenses, and does all the other work needed to make the software available.
- PaaS: A platform provides a complete solution for running software in an integrated manner on a particular piece of hardware. For example, Windows is a particular kind of platform. The virtual platform provided by PaaS allows a customer to develop, run, and manage applications of all sorts.
Defining IaaSThe simplest way to view IaaS is as a means of providing access to virtualized computer resources over an Internet connection. IaaS acts as one of three methods of sharing resources over the Internet, alongside SaaS and PaaS. AWS supports IaaS by providing access to virtualized hardware, software, servers, storage, and other infrastructure components. In short, you can use IaaS to replace every physical element in your computing setup except those required to establish and maintain Internet connectivity and those required to provide nonvirtualized services (such as printing). The advantages of IaaS are many, but here are the ones that most people consider essential:
- The host handles tasks such as system maintenance, backup, and resiliency planning.
- A client can gain immediate access to additional resources when needed and then doesn't need to worry about getting rid of them when the need has ended.
- Detailed administrative tasks are handled by the host, but the client can manage overall administrative tasks, such as deciding how much capacity to use for a particular task.
- Users have access to desktop virtualization, which means that their desktop appears on whatever device they happen to use at a given moment.
- The use of policy-based services ensures that users must still adhere to company requirements when using computer resources.
- All required updates (software and hardware) occur automatically and without any interaction required by the client.
Keep in mind that there is no free lunch. AWS and other IaaS providers are interested in making a profit. They do so by investing in huge quantities of hardware, software, and management personnel to oversee it all. The benefits of scale help create profit, and many businesses simply can't create setups they require for less money.However, you must consider the definite disadvantages of IaaS as well:
- Billing can become complex because some services are billed at different rates and within different time frames. In addition, billing can include resource usage. The client must ensure that the amount on the bill actually matches real-world usage; paying too much for services that the client didn't actually use can easily happen.
- Systems management monitoring becomes more difficult. The client loses control over the precise manner in which activities occur.
- A lag often occurs between the time a change in service is needed and the host provides it, so the client can find that even though services are more flexible, they aren't as responsive.
- Host downtime can affect a large group of people and prove difficult to fix, which means that a particular client may experience downtime at the worst possible time without any means to resolve it.
- Building and testing custom applications can become more difficult. Many experts recommend using in-house equipment for application development needs to ensure that the environment is both protected and responsive.
IaaS service contracts vary a great deal between vendors. Even though this book focuses on AWS, you need to consider other offerings, including Windows Azure, Google Compute Engine, Rackspace Open Cloud, and IBM SmartCloud Enterprise. In some cases, you might actually find it useful to obtain services from multiple hosts to obtain the best service for a particular need.
Comparing IaaS to SaaSSaaS is all about cloud-based applications. Products like online email and office suites are examples of cloud-based applications. A client typically accesses the application using a local application, such as a browser. The browser runs on local hardware, but the application runs on the host hardware. What a client sees is the application running in the browser as if it is working locally. In most cases, the application runs within a browser without any alteration to the local system. However, some applications do require the addition of plug-ins.
The difference between IaaS and SaaS is the level of service. When working with IaaS, a client typically requires detailed support that spans entire solutions. A SaaS solution may include only the application. However, it can also include the following:
- Application runtimes
- Data access
- Operating system support
- Server access
- Data storage
SaaS typically keeps the host completely in control and doesn't offer any sort of monitoring. Even though the host keeps the application updated and ensures data security, the client company administrators typically can't access SaaS solutions in any meaningful way (SaaS offers application usage, but not necessarily application configuration, and is therefore not as flexible as other alternatives). In addition, the client company typically accepts the application as is, without any modifications or customizations. Using client-developed applications is out of the question in this scenario.
Comparing IaaS to PaaSPaaS is more of a development solution than a production environment solution. A development team typically uses PaaS to create custom solutions or modify existing solutions. The development staff has full control over the application and can perform all development-related tasks, such as debugging and testing. As with the SaaS solution, the host normally maintains control over
- Operating system support
- Server access
- Data storage
- High availability
- SaaS enablement
Administrators can also perform monitoring and management tasks within limits when working with a PaaS (depending on the contract the client has with the host). However, realize that PaaS is oriented toward development needs, so the developer takes precedence when it comes to performing some tasks that an administrator might normally perform. In addition, PaaS relates to development, not production setups, so the host may take care of all administration tasks locally.