Cloud Models: Public, Private, and Hybrid
Not all clouds are the same. Public cloud is like renting an apartment, private cloud is like owning a house, and hybrid cloud is the best of both. Let's explore when to use each.
What are cloud models?
Think of it like housing.
Public cloud = renting an apartment. Someone else owns the building, maintains it, and shares it with other tenants. You just pay rent and move in.
Private cloud = owning your own house. You control everything — the locks, the garden, the walls. But YOU pay for all the maintenance.
Hybrid cloud = you own a house but also rent a holiday apartment. Some things stay at home (private), and for special occasions you use the rental (public).
Each model has trade-offs. The exam tests whether you can pick the right one for the right situation.
The three cloud models compared
| Feature | Public Cloud | Private Cloud | Hybrid Cloud |
|---|---|---|---|
| Who owns the hardware? | Cloud provider (Microsoft, AWS, etc.) | Your organisation (or a dedicated hosting provider) | Mix — some yours, some provider's |
| Who manages it? | Cloud provider | Your IT team (or outsourced) | Both — shared management |
| Shared with others? | Yes — multi-tenant | No — single tenant | Private part is single-tenant |
| Cost model | Pay-as-you-go (OpEx) | Large upfront investment (CapEx) | Mix of both |
| Scalability | Virtually unlimited | Limited by your hardware | Scale to public when needed |
| Best for | Most workloads, startups, rapid growth | Strict compliance, legacy apps | Regulated industries with burst needs |
When to use each model
Public cloud — Peak Roasters’ choice
Peak Roasters, a small coffee roastery with 15 staff, needs a website, email, and an ordering system. They don’t have an IT team or a server room.
Public cloud is perfect because:
- No upfront hardware costs — they pay monthly
- Microsoft handles all the maintenance
- They can scale up during holiday seasons and scale back after
- They get enterprise-grade security without hiring specialists
Exam pattern: Public cloud is the default recommendation for most scenarios on the exam unless there’s a specific compliance or control requirement.
Private cloud — Harbour Health’s requirement
Harbour Health, a healthcare company with 500 staff, must comply with strict health data regulations. Some patient records cannot leave their data centre.
Private cloud makes sense because:
- Full control over data location and access
- Can meet specific regulatory requirements
- Customised security policies
- Dedicated resources — no “noisy neighbours”
Private cloud doesn't always mean on-premises
A common misconception: private cloud doesn’t mean you must own physical servers. You can have a hosted private cloud where a provider dedicates hardware exclusively to your organisation.
The key distinction is single-tenant (only your organisation uses those resources) vs multi-tenant (shared with others).
Exam tip: If a question mentions “dedicated hardware” or “single-tenant,” think private cloud — even if it’s hosted by a provider.
Hybrid cloud — Harbour Health’s actual solution
In practice, Harbour Health uses hybrid cloud. Patient records stay on their private infrastructure, but they use Azure (public cloud) for:
- Email and collaboration (Microsoft 365)
- Development and testing environments
- Analytics and reporting (de-identified data)
- Burst capacity during flu season
Hybrid cloud is best when you need both control AND flexibility.
Multi-cloud vs hybrid cloud
Don’t confuse these two terms:
- Hybrid cloud = public cloud + private cloud working together
- Multi-cloud = using multiple public cloud providers (e.g., Azure AND AWS)
Multi-cloud is common in large enterprises for redundancy or to use best-of-breed services. The AZ-900 exam focuses on hybrid cloud but may mention multi-cloud in passing.
The consumption-based model
Cloud computing uses a consumption-based model — you only pay for what you actually use.
| Traditional IT (CapEx) | Cloud (OpEx) |
|---|---|
| Buy servers upfront | Pay monthly for resources used |
| Pay whether you use them or not | Pay only for what you consume |
| Expensive to scale | Scale instantly, pay more only when needed |
| Hardware depreciates over time | Always get the latest infrastructure |
| Budget months in advance | Predictable monthly bills |
CapEx (Capital Expenditure) = big upfront purchases. Buying servers, building data centres.
OpEx (Operational Expenditure) = ongoing monthly costs. Paying for cloud services as you use them.
Key exam concept: Cloud shifts IT spending from CapEx to OpEx. This is a fundamental selling point of cloud computing and a heavily tested concept.
Summit Construction used to spend $50,000 every three years on new servers. Now they spend $800/month on Azure — and they can increase or decrease that spending instantly based on project load.
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Cloud Models: Public, Private, and Hybrid — AZ-900
Cloud Models: Public, Private, and Hybrid — AZ-900
~9 minFlashcards
Knowledge Check
Peak Roasters needs a website and email for 15 staff. They have no IT team and want minimal upfront costs. Which cloud model is most appropriate?
Harbour Health stores patient records that must stay within their own data centre due to regulations. They also want to use cloud services for email and analytics. Which cloud model best fits their needs?
Which statement correctly describes the consumption-based model of cloud computing?
Next up: How cloud pricing works — consumption, reserved, and serverless models explained.