Cloud Service Models: IaaS, PaaS, and SaaS
💡 Quick Tip
Technical Tip: Choose IaaS if you need full OS control; choose PaaS if you only want to upload code and forget the rest.
The Cloud Computing Hierarchy
Cloud Computing is not a single product, but a set of models delegating different technical responsibility levels to the provider. Understanding where provider responsibility (like AWS or Azure) ends and user responsibility begins is vital for secure design.
IaaS (Infrastructure as a Service)
The lowest level. The provider delivers raw resources: VMs, networking, and storage.
- Your responsibility: Installing the OS, managing security patches, and optimizing databases.
- Examples: Amazon EC2, Google Compute Engine.
PaaS (Platform as a Service)
The provider manages the OS, runtime, and web server. You only provide your application code.
- Your responsibility: Business logic and code.
- Advantages: Transparent auto-scaling and fast deployment.
SaaS (Software as a Service)
The highest level, where you consume a finished app via a browser.
- Your responsibility: Only user data and configuration.
- Examples: Microsoft 365, Slack.
📊 Practical Example
Real-World Scenario: Choosing a Strategy for a Data Analysis App
Step 1: IaaS Option. They consider renting servers with GPUs. This gives full control but requires a full-time sysadmin for security and updates.
Step 2: PaaS Option. They evaluate a service that offers a pre-configured Python runtime. It is pricier per hour, but scaling is automatic during analysis spikes.
Step 3: Technical Decision. They use a hybrid architecture: PaaS for the web frontend (development speed) and IaaS for heavy calculation engines (hardware optimization).
Step 4: Security Audit. They review the shared responsibility model. In PaaS, the provider secures the OS; in IaaS, they must run apt upgrade weekly themselves.
