Stage 7 · Master
AZ-900 — Azure Fundamentals
Cloud Concepts (25%)
IaaS/PaaS/SaaS, shared responsibility, and cloud models — the foundation of Azure knowledge.
What Is Cloud Computing?
Cloud computing is the delivery of computing services — servers, storage, databases, networking, software, analytics — over the internet. Instead of owning physical hardware, you rent resources from a cloud provider and pay for what you use.
- On-demand self-service — Provision resources without human interaction.
- Broad network access — Services available over the network from any device.
- Resource pooling — Provider resources serve multiple consumers.
- Rapid elasticity — Scale up or down quickly.
- Measured service — Pay only for what you use.
Service Models: IaaS, PaaS, SaaS
Cloud services are categorized by how much the provider manages vs. how much you manage. Understanding these models is fundamental to the AZ-900.
| Model | You Manage | Provider Manages | Example |
|---|---|---|---|
| IaaS | OS, runtime, apps, data | Physical hardware, networking | Azure VMs, AWS EC2 |
| PaaS | Applications and data | OS, runtime, middleware, hardware | Azure App Service, Heroku |
| SaaS | Nothing (just use it) | Everything | Microsoft 365, Salesforce |
IaaS gives you the most control but also the most responsibility. SaaS gives you the least control but also the least responsibility. PaaS is the middle ground — you focus on your code, the provider handles everything else.
Shared Responsibility Model
Security and compliance are shared between the provider and the customer. The provider secures the infrastructure. The customer secures what they put on the infrastructure. This model applies to all cloud service types.
| Model | Provider Secures | Customer Secures |
|---|---|---|
| IaaS | Physical, network, hypervisor | OS, runtime, apps, data, identity |
| PaaS | Physical through runtime | Applications, data, identity |
| SaaS | Everything | Data, user access, device management |
Public, Private, Hybrid, Multi-Cloud
- Public cloud — Resources owned and operated by a third-party provider (Azure, AWS, GCP).
- Private cloud — Cloud infrastructure used exclusively by one organization.
- Hybrid cloud — Combines public and private clouds with orchestration between them.
- Multi-cloud — Uses multiple public cloud providers simultaneously.
The exam tests your understanding of when to use each model. Use public cloud for scalability and cost. Use private cloud for compliance and control. Use hybrid for flexibility. Know the Azure Hybrid Benefit for cost savings.
CapEx vs. OpEx
Cloud computing shifts IT spending from capital expenditure (CapEx) to operational expenditure (OpEx). Instead of buying hardware upfront, you pay for services monthly. This has significant financial implications.
| Type | Description | Example |
|---|---|---|
| CapEx | Upfront capital investment in hardware | Buying servers, networking equipment |
| OpEx | Ongoing operational costs | Azure monthly billing, SaaS subscriptions |
Benefits of Cloud Computing
- High availability — Redundancy across regions and availability zones.
- Scalability — Scale resources up or down based on demand.
- Elasticity — Automatically adjust capacity to match load.
- Reliability — Built-in disaster recovery and backup.
- Global reach — Deploy resources worldwide in minutes.
- Speed and agility — Provision infrastructure in minutes, not months.
Key Terms to Memorize
- Availability Zones — Physically separate locations within a region.
- Regions — Geographic areas with one or more data centers.
- Resource Groups — Logical containers for Azure resources.
- SLA — Service Level Agreement (uptime guarantee).
- Fault tolerance — System continues operating despite failures.
- Disaster recovery — Recovering from a catastrophic event.
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