Part 4: Cloud Service Models: IaaS, PaaS & SaaS Architecture Explained
Lesson Focus & Objectives
The cloud services industry organizes offerings into three hierarchical abstraction tiers: Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS). Understanding where the boundary of engineering responsibility lies between your organization and the cloud provider is essential for compliance, operational efficiency, and cost optimization. In Part 4, we examine the technical mechanics of each service model and dissect the formal Shared Responsibility Security Model.
1. The Cloud Service Pyramid Explained
1. Infrastructure as a Service (IaaS)
Lowest Abstraction / Maximum ControlProvides the consumer with raw compute resources (virtual or bare-metal CPU, RAM), raw storage capacity, and virtual networking components (subnets, routers, firewalls). The consumer has full administrative root access to install, configure, and operate arbitrary operating systems (Linux, Windows Server), database engines, and runtime dependencies.
2. Platform as a Service (PaaS)
Managed Runtime / Developer VelocityProvides consumers with a fully managed application development and runtime environment. The cloud provider automatically provisions, scales, and patches underlying operating systems, container engines, hardware virtualization, and middleware. The consumer only deploys application source code, configures environment variables, and manages database schema definitions.
3. Software as a Service (SaaS)
Turnkey Application / End-User ConsumptionProvides complete, fully managed applications delivered over the web browser or mobile client on a subscription basis. The provider manages 100% of the underlying infrastructure, code deployments, automated database backups, security patches, and hardware scaling. Consumers only manage user accounts, roles, and tenant-specific configuration settings.
2. The Shared Responsibility Matrix
| Infrastructure Layer | On-Premises | IaaS | PaaS | SaaS |
|---|---|---|---|---|
| Data & User Access | Customer | Customer | Customer | Customer |
| Application Code & Binaries | Customer | Customer | Customer | Cloud Provider |
| Runtime & Middleware (PHP, Node, Java) | Customer | Customer | Cloud Provider | Cloud Provider |
| Operating System & Security Patching | Customer | Customer | Cloud Provider | Cloud Provider |
| Hypervisor & Virtualization Layer | Customer | Cloud Provider | Cloud Provider | Cloud Provider |
| Physical Servers, Disks & Facilities | Customer | Cloud Provider | Cloud Provider | Cloud Provider |
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