Cloud Computing Models: IaaS, PaaS and SaaS

Cloud services are grouped into Infrastructure as a Service, Platform as a Service, and Software as a Service, depending on how much the provider manages for you. Understanding where your responsibility ends and the provider's begins is one of the most tested ideas on the Cloud Digital Leader exam.

Key facts

• Infrastructure as a Service provides virtualized computing, storage, and networking on demand, while the customer still manages the operating system, runtime, and applications running on top.
• Platform as a Service provides a managed platform for building and running applications, so developers focus on code and data while the provider handles servers, patching, and scaling plumbing.
• Software as a Service delivers complete applications over the internet, such as email and collaboration tools, with the provider managing nearly everything except user access and data.
• As you move from IaaS to PaaS to SaaS, you trade direct control for convenience, speed, and reduced operational work for your internal teams.
• Google Cloud examples help anchor the models: Compute Engine is IaaS, App Engine and Cloud Run are PaaS-style services, and Google Workspace is SaaS.
• All three models still run on shared cloud infrastructure with pay-as-you-go billing, elasticity, and global reach provided by the cloud provider.
• Choosing a model is a business decision about skills, speed, customization needs, and compliance, not simply a technical preference of the engineering team.
• Many organizations use all three models at once for different workloads, rather than committing the entire company to a single delivery model.

What the exam expects you to know

• The exam tests matching a scenario to IaaS, PaaS, or SaaS based on how much control the customer needs and how much management they want to avoid.
• Expect questions about total cost of ownership, where reduced operational effort can offset service fees even when raw infrastructure looks cheaper.
• Candidates should know concrete Google Cloud examples for each model and be able to explain them to a non-technical stakeholder clearly.
• Scenarios often describe a team that wants to focus only on code, which points to PaaS, or only on using software, which points to SaaS.
• The exam also tests the shared responsibility implications of each model, because responsibility shifts toward the provider as you move toward SaaS.
• Questions may contrast cloud models with on-premises computing, where the organization manages every layer from hardware through applications itself.

Cloud Computing Models: IaaS, PaaS and SaaS vs On-premises computing: when to use which

Cloud models differ from on-premises computing mainly in ownership, speed, and financial treatment. On-premises, an organization buys, installs, and maintains its own hardware and software, which gives maximum control but requires capital spending, long procurement cycles, and in-house maintenance. With IaaS, PaaS, or SaaS, resources are rented on demand, capacity can grow or shrink quickly, and the provider handles the underlying facilities and much of the upkeep. Choose on-premises only when regulation, legacy constraints, or very specific control needs demand it. For most new initiatives, a cloud model reduces time to value and lets small teams deliver results that would otherwise need large infrastructure investment. See also the On-premises computing notes.

Common exam traps

• Thinking SaaS means the customer has no responsibilities at all, when users, access settings, and the data entered into the application remain the customer's concern.
• Assuming IaaS is always cheapest, without counting the staff time needed to patch, secure, back up, and manage the operating systems yourself.
• Confusing PaaS with SaaS, even though PaaS is for building your own applications while SaaS is finished software you simply use.
• Believing an organization must pick only one model, when real portfolios almost always mix models to match different workload needs.

Frequently asked questions

What is the main difference between IaaS and PaaS?

With IaaS you rent infrastructure and manage the operating system, middleware, and applications yourself, giving you the most control. With PaaS the provider also manages the platform layer, so your team focuses mainly on writing code and managing data, which speeds development and reduces routine operational work.

When should a business choose SaaS?

Choose SaaS when a standard application meets your needs and you want the fastest adoption with the least technical management, such as for email, collaboration, or customer relationship tools. The provider handles updates, availability, and security of the application itself, while you manage users and configuration.

Can a company use IaaS, PaaS, and SaaS together?

Yes, and most do. A company might run a specialized legacy system on IaaS virtual machines, build a new customer app on a PaaS service, and use SaaS for office productivity. Matching each workload to the model that fits its control and speed needs is normal practice.

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