Describe Cloud Concepts · Topic 1 of 3
Cloud Computing, Shared Responsibility and Cloud Models
Learn AZ-900 cloud basics: what cloud computing is, the shared responsibility model, public, private and hybrid clouds, consumption pricing and serverless.
- 6 min
- Microsoft always secures the physical datacenter. You always secure your data, accounts and identities, and you protect your own devices.
- The operating system is your job in IaaS and Microsoft's job in PaaS and SaaS.
- Public cloud has shared hardware and no purchase cost. Private cloud is used by one organization. Hybrid combines both.
What it is
Cloud computing means renting computing services over the internet instead of buying and running your own hardware. The services include servers, storage, databases, networking and software.
You use what you need and pay for what you use, while the provider runs the datacenters. This topic covers who is responsible for what, where the cloud runs, and how you pay.
How it works
The shared responsibility model
Microsoft is always responsible for the physical datacenters, the physical network and the physical hosts. You are always responsible for your data and for your accounts and identities, and you stay responsible for protecting the devices people use to connect.
Everything in between moves toward Microsoft as the service becomes more managed.
| Layer | On premises | IaaS | PaaS | SaaS |
|---|---|---|---|---|
| Data, accounts and identities | You | You | You | You |
| Applications | You | You | Shared | Shared |
| Operating system | You | You | Microsoft | Microsoft |
| Physical hosts, network and datacenter | You | Microsoft | Microsoft | Microsoft |
No cloud service moves responsibility for your data or your user accounts to the provider. These stay with you in every model.
Cloud models
A cloud model describes who owns the infrastructure and who can use it.
| Model | What it is | Typical use |
|---|---|---|
| Public cloud | Owned and run by a provider, hardware shared between many customers, no purchase cost | Variable workloads, testing, fast starts |
| Private cloud | Used by one organization, in its own datacenter or hosted for it, which maintains it | Strict rules about data or full control |
| Hybrid cloud | A public and a private cloud connected and used together | Keeping sensitive data on premises while using the cloud for extra capacity |
A hybrid cloud lets you move to the cloud in steps and keep systems that cannot move yet. Multicloud is different: it uses more than one public cloud provider.
The consumption-based model
In the consumption-based model you pay only for what you use and there is no large purchase up front. This changes the type of spending.
- Capital expenditure (CapEx) is spending up front on physical assets such as servers and buildings.
- Operational expenditure (OpEx) is spending on services as you use them, billed as a running cost.
The cloud moves spending from CapEx to OpEx. You also stop guessing future capacity, because you add or remove resources as demand changes.
Comparing cloud pricing models
Azure offers several ways to pay for the same compute resource.
| Pricing model | How it works | Best for |
|---|---|---|
| Pay as you go | Billed for usage with no commitment | Short or unpredictable use |
| Reserved capacity | Commit for one or three years for a discount | Steady, predictable use |
| Savings plan for compute | Commit to an hourly spend for one or three years for a discount that applies across services | Steady spend with flexibility |
| Spot | Deep discount on spare capacity that Azure can take back | Work that can stop and restart |
Serverless
Serverless computing lets you run code without managing servers. The provider handles the servers, scales them automatically and charges for the time your code runs.
Servers still exist, but you do not provision or manage them. Azure Functions runs code in response to events, and Azure Logic Apps builds workflows in the same style.
Choosing a cloud model
Exam questions describe a company and ask which model fits. Read for the constraint that decides it.
| Situation | Best fit | Why |
|---|---|---|
| A retailer needs far more capacity for two months a year | Public cloud | Capacity is added on demand and paid for only while used |
| A bank must keep customer records in its own datacenter but wants cloud analytics | Hybrid cloud | Sensitive data stays on premises while the cloud adds scale |
| A government agency must control all of its own hardware | Private cloud | One organization owns and operates the infrastructure |
| A company uses Azure for some workloads and another public provider for others | Multicloud | More than one public provider is used |
A worked example: CapEx against OpEx
A company needs ten servers for a new project. Buying them is capital expenditure: the money is spent up front, the servers must be housed and maintained, and they are paid for even if the project ends early.
Running the same workload in Azure is operational expenditure. The company pays a monthly bill that rises and falls with use, and stops paying when it deletes the resources. This is why the consumption-based model suits projects whose size is hard to predict.
Other ways to lower the price
Besides reservations and spot, there is Azure Hybrid Benefit. It lets you use existing Windows Server and SQL Server licenses, when they include Software Assurance or a qualifying subscription, on Azure at a lower rate. It combines with reserved capacity for a larger saving.
| Option | Saves money by |
|---|---|
| Reserved capacity | Committing to one or three years of use |
| Savings plan for compute | Committing to an hourly spend |
| Spot | Using spare capacity that can be taken back |
| Azure Hybrid Benefit | Reusing licenses you already own |
How the exam asks about this
- "Which party is responsible for the physical security of the datacenter?" The answer is always Microsoft.
- "A company wants to avoid buying hardware and pay monthly." This is consumption-based, operational expenditure.
- "Which model lets the company keep some systems on premises?" Hybrid.
- "Which pricing option suits a job that can be interrupted?" Spot.
- Watch for answers that describe CapEx as a cloud benefit. Up-front hardware spending is the opposite of what the cloud offers.
What to remember for the exam
- Microsoft always secures the physical datacenter. You always secure your data, accounts and identities, and you protect your own devices.
- The operating system is your job in IaaS and Microsoft's job in PaaS and SaaS.
- Public cloud has shared hardware and no purchase cost. Private cloud is used by one organization. Hybrid combines both.
- Consumption-based pricing means you pay for what you use. Cloud spending is OpEx, not CapEx.
- Reserved capacity and savings plans trade a commitment for a discount. Spot is cheapest but can be interrupted.
- Serverless means you do not manage servers, and you are billed for execution.
"Pay only for what you use" points to the consumption-based model. "Spare capacity at a deep discount" points to spot. "Public and private together" points to hybrid.
Common mistakes
Thinking the provider secures everything. Your data and your accounts and identities always remain your responsibility.
Mixing up hybrid and multicloud. Hybrid combines public and private clouds. Multicloud uses several public cloud providers.
Calling cloud spending CapEx. Buying servers is CapEx. Paying for cloud services as you use them is OpEx.
Taking serverless literally. There are servers, but the provider manages them and you never provision them.
Check yourself
Who is always responsible for the physical datacenter in Azure?
Microsoft, in every service type.
Which cloud model combines a public cloud with a private cloud?
Hybrid cloud.
What type of spending does the consumption-based model replace?
Capital expenditure (CapEx), which becomes operational expenditure (OpEx).
Topic 1 of 3 in Describe Cloud Concepts
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