What the cloud is and why businesses buy it
Cloud computing is renting computing resources, such as servers, storage, databases, networking and software, over the internet from a provider that owns and runs the data centers. You pay for what you use, the way you pay for electricity, instead of buying equipment up front.
A workplace picture: a clinic needs a new scheduling server. On premises, IT orders hardware, waits weeks for delivery, racks it, installs an operating system and sizes it for the busiest day of the year. In the cloud, an administrator picks a server size in a web console, has it running in minutes, and can make it smaller or larger later.
The US National Institute of Standards and Technology (NIST) defines cloud computing by five essential characteristics. The AWS exam does not quote them, but they explain why the cloud behaves the way it does.
| Characteristic | What it means | Example |
|---|---|---|
| On-demand self-service | Users create resources themselves, without asking the provider | A developer starts a test server at night without opening a ticket |
| Broad network access | Resources are reached over the network from many kinds of devices | Staff open the same app from laptops and phones |
| Resource pooling | The provider serves many customers from shared hardware | Thousands of companies share the data centers in one AWS Region |
| Rapid elasticity | Capacity grows and shrinks quickly, often automatically | An online store adds servers for a holiday sale and removes them after |
| Measured service | Usage is metered, monitored and billed | The monthly bill lists compute hours and gigabytes stored |
AWS states the business case as six advantages of cloud computing. Learn them by name: exam questions use this wording.
| Advantage | Plain meaning | Example |
|---|---|---|
| Trade fixed expense for variable expense | Pay only when you use resources, instead of buying servers before you know how they will be used | A startup pays a monthly bill that follows its traffic instead of buying a rack of servers |
| Benefit from massive economies of scale | AWS combines the usage of a huge number of customers, so its pay-as-you-go prices are lower than one company could get alone | A small firm pays a per-hour price no single buyer could negotiate with a hardware vendor |
| Stop guessing capacity | Scale up or down as demand changes, with a few minutes' notice | A tax-preparation firm handles the April peak without owning idle servers the rest of the year |
| Increase speed and agility | New resources are a click away, so trying an idea takes minutes instead of weeks | A team tests three designs in one afternoon and keeps the best |
| Stop spending money running and maintaining data centers | Spend effort on the business, not on racking, stacking and powering servers | IT staff stop replacing failed disks and start improving the patient portal |
| Go global in minutes | Deploy in Regions around the world with a few clicks, for lower latency | A US retailer serves European shoppers from a Region in Europe |
A memory chain for the six advantages: pay as you go, buy in bulk, stop guessing, move fast, skip the data center, go global.
Three more words appear in many questions:
- High availability: the system keeps working when a part fails, usually because it runs in more than one place, such as two or more Availability Zones.
- Elasticity: capacity follows demand automatically, adding resources under load and removing them when load drops, so you stop paying for idle capacity.
- Agility: the organization can try, change and release things quickly because resources are an API call away.
Scalability and elasticity are close but not the same. Scalability is the ability to grow to handle more load. Elasticity adds automatic shrinking. When a question says resources are added and removed automatically and you pay only for what you need, the answer is elasticity.
The global infrastructure is part of the value proposition too: speed of deployment (minutes, not months), global reach (Regions on several continents) and lower latency for users far from headquarters. Unit 3 covers how Regions and Availability Zones work.
Word bank
All definitions →- Cloud computing
- On-demand delivery of IT resources over the internet with pay-as-you-go pricing.
- Economies of scale
- Lower unit prices that come from operating at very large volume.
- Elasticity
- Automatically adding and removing resources to match demand.
- High availability
- Designing a system so it keeps working when a component fails.
- Variable expense
- A cost that rises and falls with usage, instead of a fixed up-front purchase.
Knowledge check
An accounting firm's workload triples every spring and drops for the rest of the year. Which advantage of cloud computing lets it avoid buying servers sized for the spring peak?
Which statement best describes elasticity?