Study Hub / Microsoft Azure Fundamentals (AZ-900) / Domain 1.0
Microsoft Azure Fundamentals (AZ-900) Domain 1.0: Describe Cloud Concepts — Explained
Domain 1.0 is the foundation the whole AZ-900 stands on: what cloud computing is, why businesses adopt it, how costs shift from CapEx to OpEx, and the deployment models Azure offers. Pure concept — learn it once, use it everywhere.
Cloud computing, defined
Cloud computing is the on-demand delivery of computing resources — servers, storage, databases, networking, software — over the internet, with pay-as-you-go pricing.
- On-demand self-service — provision what you need, when you need it, without human interaction with the provider.
- Elasticity — scale out automatically as demand rises, scale in when it falls. You stop paying for idle peak capacity.
- Measured service / pay-as-you-go — metering makes costs track usage. Turn it off, stop paying.
- Global reach — deploy to Azure regions worldwide, placing resources near your users for latency and compliance.
- High availability baked in — availability zones (separate data centers within a region) protect against facility-level failure.
CapEx vs. OpEx: the money shift
- CapEx (capital expenditure) — buying assets upfront: servers, racks, data-center build-out. Big initial spend, then depreciation. The on-premises model.
- OpEx (operational expenditure) — paying for services as consumed: this month's VM hours, this month's storage. The cloud model.
- Why it matters — OpEx removes the upfront barrier (startups can start), converts fixed costs to variable ones, and shifts financial risk from "did we buy the right size?" to "are we using what we pay for?"
- Consumption-based model — you pay for what you use, like electricity. No usage, no bill (for metered services).
Deployment models and cloud types
- Public cloud — shared infrastructure owned by the provider (Azure). Cheapest, most elastic, least direct control.
- Private cloud — dedicated infrastructure for one organization (on-premises or hosted). Most control, highest cost, least elasticity.
- Hybrid cloud — public + private working together. Keep sensitive workloads private, burst elastic ones public. Azure Arc extends Azure management to hybrid resources.
- Service models — IaaS (rent VMs — you manage the OS), PaaS (rent a platform — provider manages the OS), SaaS (rent software — provider manages everything).
- Shared responsibility — Microsoft secures the physical hosts, network, and hypervisor; you secure your data, identities, and configurations. The customer always owns their data and access.
The must-memorize table: CapEx vs. OpEx
The money question behind half of Domain 1.
| Aspect | CapEx (on-premises) | OpEx (cloud) |
|---|---|---|
| Spending pattern | Large upfront purchase | Pay as you go |
| Cost behavior | Fixed — you own the capacity | Variable — scales with usage |
| Risk | Overbuy (waste) or underbuy (outage) | Overspend if unmanaged — needs cost controls |
| Barrier to start | High — procure and install first | Low — provision in minutes |
| Example | Buying servers for a new app | Running the app on Azure VMs |
Try it: 4 sample questions
Sample questions to check your understanding of this domain. Answers and full reasoning are tucked under each one.
1. A startup wants to launch an app without buying any servers, paying only for what the app actually uses. Which model fits?
- A. A. CapEx — purchase infrastructure upfront
- B. B. OpEx — consumption-based cloud spending
- C. C. Private cloud — dedicated hardware
- D. D. Capital leasing — finance the servers
Show answer & reasoning
B. No upfront hardware plus pay-for-use is the OpEx/consumption model — the cloud's core financial pitch. CapEx (A) and leasing (D) both involve acquiring assets; private cloud (C) is still dedicated infrastructure with upfront cost.
2. A hospital must keep patient records in its own data center but run analytics on Azure. Which deployment model is this?
- A. A. Public cloud
- B. B. Private cloud
- C. C. Hybrid cloud
- D. D. Multi-cloud
Show answer & reasoning
C. On-premises systems plus Azure, working together, is hybrid by definition — often driven by regulation, latency, or legacy constraints. Azure Arc is Microsoft's hybrid-management story. Multi-cloud (D) would mean multiple public providers, which isn't described here.
3. A startup's web app idles overnight but spikes every weekday at noon. Under a consumption-based model, what happens to their cloud bill?
- A. A. It stays flat — they pay the same every month
- B. B. It tracks actual usage: near-zero overnight, higher at the noon spike — they pay for what they consume
- C. C. They must prepay a year of peak capacity
- D. D. Spikes are free; only baseline usage is metered
Show answer & reasoning
B. Consumption-based = metered like a utility: the bill follows real usage up and down. Idle resources cost ~nothing; the noon spike costs more — and scaling back down stops the meter. Flat fees (A) and upfront commitments (C) are the opposite pattern (commitments can discount consumption pricing, but the metering underneath stays).
4. Under the shared responsibility model, who is responsible for the physical security of Azure data centers?
- A. A. The customer — always
- B. B. Microsoft — physical hosts and facilities are the provider's responsibility
- C. C. Both equally
- D. D. The customer's ISP
Show answer & reasoning
B. Physical security of data centers, hosts, and the hypervisor is Microsoft's side of the line — always. The customer owns what's in the cloud: data, identities, configurations. "Who secures the building?" → the provider, on every cloud exam.
This was one domain. The simulator drills all 3.
This free preview covered Describe Cloud Concepts (Domain 1.0). Not covered here: Describe Azure Architecture & Services (Domain 2.0). The largest domain — every Azure service, region, and architecture detail — stays in the paid guide and practice bank. The ByteBar Practice Exam Simulator drills every domain with 1,000 exam-style questions — $9.99 one-time unlocks all 28 exams. Prefer to read? The full AZ-900 Study Guide is in the ByteBar shop on Etsy.
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