IaaS vs. PaaS vs. SaaS: The Cloud Shared Responsibility Model
A comprehensive breakdown of cloud service tiers, infrastructure management boundaries, software patching obligations, and commercial tradeoffs.
IaaS (Infrastructure as a Service) provides raw virtualized compute, storage, and networking where the customer manages the OS, middleware, and application. PaaS (Platform as a Service) abstracts the OS and runtime, allowing developers to focus purely on deploying application code. SaaS (Software as a Service) delivers complete cloud-hosted software managed entirely by the vendor, consumed by end users via web or API.
Choosing among IaaS, PaaS, and SaaS is not merely a question of technology — it directly dictates your operational expenditure, security attack surface, regulatory liability, and engineering staffing requirements.
The Shared Responsibility Model Matrix
In all cloud deployment models, responsibility is shared between the cloud service provider (CSP) and the enterprise customer. The matrix below defines who owns each architectural layer:
| Architecture Stack Component | On-Premises Data Center | IaaS (e.g. AWS EC2, Azure VM) | PaaS (e.g. Heroku, AWS Beanstalk) | SaaS (e.g. M365, Salesforce) |
|---|---|---|---|---|
| Data & Access Governance | Customer | Customer | Customer | Customer |
| Application Code & Logic | Customer | Customer | Customer | Cloud Vendor |
| Runtime Engine & Middleware | Customer | Customer | Cloud Vendor | Cloud Vendor |
| Operating System & Kernel Patching | Customer | Customer | Cloud Vendor | Cloud Vendor |
| Hypervisor & Virtualization Layer | Customer | Cloud Vendor | Cloud Vendor | Cloud Vendor |
| Physical Servers & Power/Cooling | Customer | Cloud Vendor | Cloud Vendor | Cloud Vendor |
Key Engineering Tradeoffs
- IaaS Tradeoff: Maximum architectural control and migration ease for legacy monolithic applications, but requires dedicated Linux/Windows sysadmins for ongoing patch cycles, vulnerability management, and backup orchestration.
- PaaS Tradeoff: Drastically accelerated developer velocity with automatic scaling and zero OS patching, but introduces platform vendor lock-in and limits custom operating system-level kernel tweaks.
- SaaS Tradeoff: Zero maintenance overhead and immediate user onboarding, but demands strict identity governance (SSO/SCIM), data loss prevention (CASB/DLP), and vendor SLA monitoring.
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