1.1 What Is Cloud Computing?
Key Takeaways
- Cloud computing is the delivery of computing services over the internet, including servers, storage, databases, networking, software, analytics, and intelligence.
- Cloud computing eliminates the need to buy, own, and maintain physical data centers and servers — you rent resources on demand.
- The key shift is from Capital Expenditure (CapEx) for physical infrastructure to Operating Expenditure (OpEx) for cloud services.
- Cloud providers like Microsoft Azure manage the underlying infrastructure, allowing organizations to focus on their core business.
- The five characteristics of cloud computing (per NIST) are on-demand self-service, broad network access, resource pooling, rapid elasticity, and measured service.
What Is Cloud Computing?
Quick Answer: Cloud computing is the delivery of computing services — including servers, storage, databases, networking, software, analytics, and intelligence — over the internet ("the cloud") to offer faster innovation, flexible resources, and economies of scale. You typically pay only for the cloud services you use.
The NIST Definition
The National Institute of Standards and Technology (NIST) provides the widely accepted definition of cloud computing through five essential characteristics:
| Characteristic | Description | Azure Example |
|---|---|---|
| On-demand self-service | Provision resources without human interaction with the provider | Create a VM in the Azure portal in minutes |
| Broad network access | Resources available over the network via standard mechanisms | Access Azure services from any device with internet |
| Resource pooling | Provider's resources serve multiple consumers (multi-tenant model) | Multiple customers share physical hardware securely |
| Rapid elasticity | Scale resources up or down quickly to match demand | Azure Virtual Machine Scale Sets auto-scale based on load |
| Measured service | Resource usage is monitored, controlled, and billed transparently | Azure Cost Management tracks usage and spending in real time |
Traditional IT vs. Cloud Computing
Understanding the shift from traditional IT to cloud computing is a core AZ-900 topic:
Traditional (On-Premises) IT
- Purchase hardware upfront — servers, storage arrays, networking equipment
- Build and staff your own data centers with power, cooling, and physical security
- Estimate capacity months or years in advance (risk of over-provisioning or under-provisioning)
- Maintain everything: hardware replacements, OS patching, firmware updates, security
- Capital expenditure (CapEx): Large upfront investment before generating any value
- Long provisioning times: Weeks to months to procure and set up new hardware
Cloud Computing (Azure)
- Rent resources on demand — no upfront hardware purchases
- Microsoft manages the data centers, hardware, cooling, power, and physical security
- Scale dynamically — add or remove resources in minutes based on actual demand
- Pay only for what you use — metered billing with per-second or per-minute granularity
- Operating expenditure (OpEx): Variable cost based on consumption
- Fast provisioning: Deploy new resources in seconds or minutes
On the Exam: Expect questions comparing traditional IT with cloud computing. The key advantages to remember are: trade CapEx for OpEx, stop guessing capacity, increase speed and agility, eliminate data center management, benefit from economies of scale, and go global in minutes.
The Benefits of Cloud Computing
Microsoft articulates several key benefits of cloud computing that are frequently tested on the AZ-900:
High Availability
Cloud providers design infrastructure with redundancy at every level — power, networking, storage, and compute. Azure guarantees uptime through Service Level Agreements (SLAs), often 99.9% or higher for most services. If a component fails, Azure automatically fails over to a healthy component.
Scalability
The ability to adjust resources to meet demand:
- Vertical scaling (scale up/down): Increase or decrease the processing power of an existing resource (e.g., upgrade a VM from 4 vCPUs to 8 vCPUs)
- Horizontal scaling (scale out/in): Add or remove instances of a resource (e.g., go from 2 VMs to 10 VMs)
Elasticity
Elasticity goes beyond scalability — it is the ability to automatically scale resources based on real-time demand. Azure services like Virtual Machine Scale Sets and Azure App Service can automatically add or remove instances based on CPU usage, memory, or custom metrics.
Agility
Cloud resources can be deployed and configured quickly. What used to take weeks (ordering hardware, racking servers, installing OS) now takes minutes. This allows organizations to experiment, iterate, and innovate faster.
Geo-Distribution
Deploy your application across multiple Azure regions worldwide, placing resources closer to your users for lower latency and better performance. Azure operates in 60+ regions across 140+ countries.
Disaster Recovery
Cloud computing enables robust disaster recovery through geographic redundancy. Azure provides services like Azure Site Recovery and geo-redundant storage that replicate data across regions, ensuring business continuity even during regional outages.
CapEx vs. OpEx
| Aspect | CapEx (Capital Expenditure) | OpEx (Operating Expenditure) |
|---|---|---|
| Definition | Upfront spending on physical infrastructure | Spending on products/services as needed |
| Payment | Large one-time purchases | Pay-as-you-go monthly billing |
| Tax treatment | Depreciated over useful life | Deducted in the same year |
| Example | Buying servers for $100,000 | Paying $5,000/month for Azure VMs |
| Flexibility | Low — committed to purchased hardware | High — scale up or down as needed |
| Risk | Risk of over-provisioning or obsolescence | Pay only for what you consume |
On the Exam: CapEx vs. OpEx is a heavily tested concept. Remember that cloud computing shifts spending from CapEx (buying hardware) to OpEx (renting services). This is often described as "trading capital expense for variable expense."
Which of the following is a characteristic of cloud computing according to NIST?
Moving to the cloud shifts IT spending from:
What is the difference between scalability and elasticity?