The Cloud Service Model Spectrum
When organizations move to the cloud, they don't all do it the same way. Cloud providers offer services along a spectrum of managed responsibility — from raw infrastructure you fully control, to complete software applications you simply use. Understanding the three primary models — Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS) — is foundational to designing your cloud strategy.
The Shared Responsibility Breakdown
A useful mental model is to think about who manages what. As you move from IaaS to SaaS, the cloud provider takes on progressively more responsibility:
| Layer | IaaS | PaaS | SaaS |
|---|---|---|---|
| Physical hardware | Provider | Provider | Provider |
| Networking | Provider | Provider | Provider |
| Operating system | You | Provider | Provider |
| Runtime / Middleware | You | Provider | Provider |
| Application code | You | You | Provider |
| Data | You | You | You / Shared |
Infrastructure as a Service (IaaS)
IaaS provides virtualized compute, storage, and networking resources on demand. You get raw building blocks — virtual machines, block storage, virtual networks — and you manage everything above the hypervisor layer.
- Examples: AWS EC2, Azure Virtual Machines, Google Compute Engine, DigitalOcean Droplets
- Best for: Lift-and-shift migrations, custom OS configurations, workloads with unique software requirements
- Trade-offs: Maximum control and flexibility, but maximum operational overhead — your team patches the OS, manages security hardening, and handles scaling logic
Platform as a Service (PaaS)
PaaS abstracts away the operating system and runtime environment. Developers deploy application code and data; the platform handles patching, scaling, and runtime management. PaaS is designed to accelerate development by removing infrastructure toil.
- Examples: AWS Elastic Beanstalk, Azure App Service, Google App Engine, Heroku, Cloud Foundry
- Best for: Web application development, API backends, teams that want to focus on code rather than infrastructure
- Trade-offs: Faster time to market, less operational burden — but less control over the underlying environment and potential vendor lock-in at the platform layer
Software as a Service (SaaS)
SaaS delivers fully managed software applications over the internet. There is no infrastructure or platform to manage — you subscribe and use. The provider handles everything: uptime, updates, security patches, and scaling.
- Examples: Salesforce, Microsoft 365, Google Workspace, Slack, Zoom, Dropbox
- Best for: Business productivity tools, CRM, collaboration, email — any function where off-the-shelf software meets your needs
- Trade-offs: Minimal operational burden and fastest time to value, but least customization and data residency considerations to manage
How to Choose the Right Model
- Start with your team's capability: If you lack DevOps expertise, PaaS or SaaS reduces operational risk. If you have strong infrastructure engineers, IaaS gives you the control you need.
- Consider your application's uniqueness: Commodity functions (email, HR) are SaaS candidates. Custom applications benefit from PaaS or IaaS.
- Evaluate compliance requirements: Data sovereignty, encryption key management, and audit logging requirements can constrain which layers you can delegate to a provider.
- Think about cost at scale: SaaS per-seat pricing can become expensive at scale; IaaS gives you more levers to optimize costs for large workloads.
The Reality: Most Organizations Use All Three
A typical enterprise runs SaaS for productivity tools, PaaS for custom application development, and IaaS for workloads requiring specialized OS-level configuration or lift-and-shift migrations. Designing a coherent strategy across all three — with clear governance on data, identity, and cost — is the real challenge and opportunity of modern cloud adoption.