Another as a Service? What is The Difference Between IaaS, CaaS, PaaS, and FaaS?

One of the biggest trends in enterprise IT over the past decade is the explosion of the “as a service” business model, also known by the acronym XaaS. In the XaaS model, businesses provision services and applications over the Internet, rather than installing them on local machines. According to a 2018 survey by Deloitte, 71 percent of organizations say that XaaS now makes up more than half of their enterprise IT.

As the XaaS model continues to grow, however, it’s become harder and harder to keep track of all the various offerings and acronyms. In this article, we’ll discuss the differences between IaaS, CaaS, PaaS, and FaaS, so that you can determine which of these possibilities is the best fit for your IT needs.

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What is IaaS (infrastructure as a service)?

You can think of XaaS offerings as a spectrum:

  • On one end of the spectrum is the traditional “on-premises” model, in which the entire IT infrastructure operates locally: from the software applications you use to the servers that they run on.
  • On the other end of the spectrum is the “fully managed” model, in which a third-party cloud provider handles all aspects of provisioning and managing the software and hardware for you.

Of the four “as a service” models that we’ll discuss in this article, IaaS (infrastructure as a service) is the closest to on-premises. In IaaS, a third-party cloud provider rents infrastructure such as servers, virtual machines (VMs), networks, and storage. However, users are still responsible for managing and provisioning this hardware and installing applications.

A common and humorous analogy for explaining the XaaS model is the idea of “pizza as a service”:

  • In on-premises pizza as a service (i.e. homemade pizza), you are responsible for providing everything from the pizza oven and dough to the toppings and dining table.
  • In fully managed pizza as a service (i.e. dining out), the restaurant provides all of the infrastructure, ingredients, and wait staff, and customers only have to pay the bill.

In this analogy, you could think of IaaS as providing the pizza-making “infrastructure,” i.e. the oven and the gas/electric utilities that power it. However, the responsibility of providing the pizza dough and ingredients, as well as other necessities such as plates, utensils, etc., will fall squarely in your lap.

What is CaaS (containers as a service)?


CaaS (containers as a service) represents the next step up from IaaS on the XaaS spectrum. In CaaS, cloud users can deploy containers, i.e. software packages that combine applications with the libraries, dependencies, and settings that they need to run predictably and reliably.

CaaS solutions provide you with everything that IaaS does—i.e. the servers, VMs, network, and storage—as well as container engines and orchestration functionality. Some examples of CaaS solutions are AWS Fargate and Google Cloud Run. The term KaaS (Kubernetes as a service) is a subclass of CaaS, used to describe the container orchestration technology Kubernetes.

What is PaaS (platform as a service)?

PaaS (platform as a service) offerings come after IaaS and CaaS on the XaaS spectrum. With PaaS, you get access to everything that IaaS gives you and more: the runtime, middleware, and operating system. As a result, users are only responsible for managing their own applications and data. (Here at, we’re very familiar with what PaaS entails: after all, we were named an “innovator” in the PaaS field by the market intelligence firm IDC!)

PaaS solutions are often intended as a framework or sandbox for developers to build their own software applications. Some popular PaaS options include Google App Engine and AWS Elastic Beanstalk.

Continuing the “pizza as a service” analogy, a PaaS restaurant would provide infrastructure such as the oven, as well as pizza dough and toppings. However, you would still have to make and cook the pizza yourself, and you might have to bring other necessities (such as drinks and silverware). Serverless Tools

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What is FaaS (function as a service)?


Last but not least, we come to FaaS (function as a service), which is the closest to the “fully managed” model on the XaaS spectrum. In FaaS, the third-party cloud provider automatically executes a given function or piece of code in response to an external trigger or event. In particular, the FaaS provider is responsible for powering up and shutting down the server on which the application runs; users pay only for the compute and storage resources they consume.

FaaS is sometimes referred to as “serverless computing,” which is a bit of a misnomer: serverless applications still require a server to run, but the user doesn’t have to worry about managing or provisioning that server.

IaaS vs. CaaS vs. PaaS vs. FaaS: Which is Right for You?

The right choice between IaaS, CaaS, PaaS, and FaaS will largely depend on the levels of responsibility and control that you want to have over your IT infrastructure:

  • IaaS is ideal if you want the benefits of the cloud (e.g. scalability, cost model, disaster recovery) while maintaining a large degree of control.
  • CaaS is good for IaaS situations where developers want to enjoy the convenience of container orchestration as well.
  • PaaS is the best choice if you don’t want to deal with the complexity and nuance of setting up servers, networks, and databases, but you do have the time, budget, and resources to build your own software applications, including a skilled team of developers.
  • FaaS is a good fit for very high-volume transactions, especially software with spikes in workload that need to be rapidly scaled, as well as applications that are run on a dynamic basis or regularly scheduled.



Whether you use IaaS, CaaS, PaaS, or FaaS, there’s a XaaS model out there that fits your needs. IronWorker is a serverless FaaS solution that makes it easy to deploy jobs in any IT environment—whether that’s in the public cloud, on-premises, on a dedicated server, or using a hybrid deployment combining the cloud and on-premises. Sound intriguing? Check out how some of the world’s most popular websites have successfully used IronWorker, or get in touch with our team today for a free trial of the IronWorker platform.

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