Public Cloud
😟 THE PROBLEM
A start-up needs servers now but has no money for hardware.
😊 THE SOLUTION
Use the public cloud: shared infrastructure, nothing to buy, pay as you go.
- No budget for servers✓ No up-front cost at all
- Nobody knows how many users will come✓ Scale with demand on shared capacity
- No staff to run hardware✓ The provider maintains everything physical
Quick answer
A public cloud is cloud infrastructure owned and operated by a third-party provider, such as Microsoft Azure, and offered to anyone over the internet. Many customers share the provider's hardware but are isolated from each other. There is no hardware to buy, you scale on demand, and you pay for what you use.
Exam objective: 1.1.3 Define cloud models, including public, private, and hybrid. 1.1.4 Identify appropriate use cases for each cloud model. (Skills measured as of July 20, 2026)
Start with a question
Why does everyone in a city share one bus network instead of each family running its own bus?
A bus network is expensive to build and run, but when thousands of people share it, each ride costs very little. You do not own the bus, but you can get on whenever you need to.
The public cloud works the same way. Microsoft builds enormous datacenters. Millions of customers share them, and each pays only for the “rides” they take.
Explain it like I’m 10
The technical explanation
A public cloud is a deployment model in which a cloud provider owns, operates and maintains the infrastructure and makes services available to the general public over the internet. Microsoft Azure is a public cloud.
The defining characteristic is multi-tenancy: the same physical servers, storage systems and network devices serve many customers (tenants). Isolation is enforced in software and hardware. Hypervisors separate virtual machines, virtual networks separate traffic, encryption protects data, and identity controls decide who can access what.
| Advantage | Why it matters |
|---|---|
| No capital expenditure | Nothing to buy; start immediately |
| Massive scale | Capacity is available when you need it |
| Pay-as-you-go | Costs follow usage |
| No hardware maintenance | The provider handles hardware, power, cooling and physical security |
| Global reach | Deploy close to users in many regions |
| Trade-off | What it means |
|---|---|
| Less physical control | You cannot choose the exact server or walk into the datacenter |
| Specific compliance needs | Some requirements may be harder to meet (check region and certification options) |
| Dependency | You rely on the provider and your connectivity |
Shared by everyone
- Datacenter buildings
- Physical servers and racks
- Power, cooling, security guards
- Global backbone network
Isolated per customer
- Your virtual machines and data
- Your virtual networks
- Your identities and permissions
- Your encryption keys (optionally)
Architect level Isolation options inside the public cloud
If a workload needs more isolation without leaving Azure:
- Azure Dedicated Host: a physical server dedicated to your organisation, with your VMs only.
- Isolated VM sizes: sizes that take a whole physical host.
- Confidential computing: VMs and containers that use hardware-based trusted execution environments (for example AMD SEV-SNP or Intel TDX), so data stays encrypted even while in use, protected from the host operator.
- Private endpoints: reach PaaS services over a private IP in your virtual network instead of a public endpoint.
These options let regulated industries use the public cloud without moving to a private cloud.
Real-world business scenario
A mobile gaming studio
- The problem
- A new game might have 1,000 players or 1,000,000 in launch week. Nobody can predict which.
- What they used
- Game servers on Azure Virtual Machine Scale Sets in several regions, player profiles in Azure Cosmos DB, leaderboards cached in Azure Managed Redis.
- Why that choice
- Only a public cloud gives instant, global capacity without buying hardware for a launch that might not take off.
- The result
- The game scaled to millions of players in its first week, and the studio paid for small capacity during testing.
When to use it and when not to
✓ Use it when…
- New applications and start-ups that need to move fast with no up-front cost.
- Variable, seasonal or unpredictable workloads.
- Global audiences that need low latency in many regions.
- Dev and test environments that are created and deleted often.
✕ Think twice when…
- You need full control of physical hardware or its exact location beyond what regions offer.
- A regulation explicitly prohibits shared or third-party infrastructure.
- Legacy systems that depend on specific on-premises hardware.
↔ Alternatives to consider
- **Private cloud** for maximum control and dedicated infrastructure.
- **Hybrid cloud** to keep some systems on-premises while using the public cloud for others.
- **Sovereign clouds** (for example Azure Government) for specific government requirements.
Interview preparation
Say your answer out loud first, then open the model answer. Interviewers care more about your reasoning than the exact words.
Beginner What is a public cloud? Give an example.
Model answer
A public cloud is computing infrastructure that a provider owns and runs, and that anyone can sign up to use over the internet. Microsoft Azure, AWS and Google Cloud are examples. You do not buy any hardware; you create resources when needed and pay for usage.
Interviewer follows up
Does "public" mean my data is public?
You
No. "Public" refers to who can become a customer, not who can see your data. Each customer's resources and data are isolated and protected by identity, encryption and network controls.
Intermediate What are the main advantages and disadvantages of public cloud?
Model answer
Advantages are no capital expense, near-unlimited scale, a pay-as-you-go model, global reach, and no hardware maintenance. Disadvantages are less control over the physical infrastructure and its location, possible difficulty meeting very specific compliance requirements, dependency on the provider and on network connectivity, and costs that need active management.
Experienced developer Security teams sometimes worry about "noisy neighbours" or side-channel attacks in multi-tenant clouds. How would you respond?
Model answer
Providers isolate tenants at the hypervisor, network and storage layers and publish their isolation design. For workloads with strict requirements, Azure offers Dedicated Hosts, isolated VM sizes and confidential computing with hardware-based trusted execution environments, which protect data while it is in use. Performance noisy-neighbour effects are managed with resource governance, and premium tiers come with defined performance targets. The real risks in practice are much more often misconfiguration and weak identity than cross-tenant attacks.
Scenario A start-up with five people needs to launch an app next month and expects unpredictable growth. Which cloud model fits?
Model answer
The public cloud. No capital spending, resources in minutes, pay only for what they use, and the ability to scale with growth. A private cloud would require hardware and skills they do not have.
Test yourself with exercises
4 original practice questions in the AZ-900 style. Pick your answers, then check them. You will see why each option is right or wrong. Score 75% or more and this topic is marked complete.
Quick revision
Key points
- Public cloud = provider-owned infrastructure available to anyone over the internet.
- Multi-tenant. Customers share hardware but are logically isolated.
- No CapEx, pay-as-you-go, rapid scaling, global reach.
- Less control over physical infrastructure; security is shared.
- Azure, AWS and Google Cloud are public clouds.
Important terminology
- Public cloud
- Cloud services owned and run by a provider and available to any organisation or person over the internet.
- Multi-tenancy
- Many customers (tenants) share the same physical infrastructure while remaining logically isolated.
- Tenant
- A customer's isolated slice of a shared service, such as their own Microsoft Entra directory.
- Dedicated host
- An option to run your VMs on a physical server not shared with other customers, still inside the public cloud.
Common mistakes
- Thinking "public" means data is publicly visible.
- Believing the public cloud has no options for dedicated or isolated hardware.
Exam tips
- "No capital expenditure" + "no hardware to maintain" + "available to anyone" = public cloud.
- Know a typical use case for each model. Public cloud suits new apps, variable demand and start-ups.
Five quick revision questions
-
1.Who owns the infrastructure in a public cloud?Show
The cloud provider.
-
2.What is multi-tenancy?Show
Many customers sharing the same infrastructure while being isolated from each other.
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3.Does public cloud require up-front hardware purchases?Show
No.
-
4.Name one disadvantage of public cloud.Show
Less physical control and possible difficulty meeting some very specific compliance requirements.
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5.Give an example of a public cloud provider.Show
Microsoft Azure (also AWS, Google Cloud).
Official references
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Next up: Private Cloud