Service Models
| Model | Full Name | Description | Azure Example |
|---|---|---|---|
| IaaS | Infrastructure as a Service | You manage OS, middleware, runtime, apps. Provider manages hardware. | Azure Virtual Machines |
| PaaS | Platform as a Service | Provider manages OS and infrastructure. You manage apps and data. | Azure App Service |
| SaaS | Software as a Service | Provider manages everything. You use the software. | Microsoft 365 |
Key Exam Point: IaaS = you patch the OS. PaaS = Microsoft patches the OS. Azure Virtual Machines = IaaS. Azure App Service = PaaS. Microsoft 365 = SaaS.
Deployment Models
- Public Cloud — Resources owned and operated by a third-party provider, shared across multiple customers. Pay-as-you-go pricing.
- Private Cloud — Resources used exclusively by one organization. May be hosted on-premises or by a third party.
- Hybrid Cloud — Combines public and private clouds, allowing data and apps to move between them.
CapEx vs. OpEx
| CapEx (Capital Expenditure) | OpEx (Operational Expenditure) | |
|---|---|---|
| Definition | Upfront investment in physical infrastructure | Pay-as-you-go, ongoing costs |
| Example | Buying servers, building a data center | Paying monthly for cloud resources |
| Cloud model | Traditional on-premises | Cloud computing |
Cloud computing shifts IT spending from CapEx to OpEx. The consumption-based model means you pay only for what you use — no upfront costs, no wasted capacity.
Shared Responsibility Model
Defines what Microsoft manages vs. what you (the customer) manage depending on the service type.
| Responsibility | On-Premises | IaaS | PaaS | SaaS |
|---|---|---|---|---|
| Physical infrastructure | Customer | Microsoft | Microsoft | Microsoft |
| Network controls | Customer | Customer | Microsoft | Microsoft |
| Operating system | Customer | Customer | Microsoft | Microsoft |
| Applications | Customer | Customer | Customer | Microsoft |
| Data & identity | Customer | Customer | Customer | Customer |
Benefits of Cloud Services
| Benefit | Definition |
|---|---|
| High Availability | Systems remain operational even when components fail. Measured by SLAs (99.9%, 99.99%). Azure guarantees uptime via Availability Zones and redundant infrastructure. |
| Scalability | Ability to handle increased load. Vertical scaling = add more power to existing VMs. Horizontal scaling = add more instances. |
| Elasticity | Automatically scale resources up when demand increases, and back down when it decreases — never over-provision or under-provision. |
| Reliability | Resilience through decentralized, distributed design. Deploy in multiple regions so a single failure doesn't take down everything. |
| Predictability | Performance predictability: auto-scaling, load balancing. Cost predictability: forecast spending with Azure Cost Management and pricing tools. |
| Security | Cloud providers offer tools and policies to meet security requirements. You choose your level of control. |
| Governance | Audit and policy enforcement built in. Templates ensure resources meet corporate standards. |
| Manageability | Manage resources via portal, CLI, APIs, or PowerShell. Auto-scaling, monitoring, and alerting included. |