Welcome to the Cloud
What cloud computing really means, how the world worked before it, and why companies of every size are moving to AWS.
Life before the cloud
Imagine you want to launch a website in 2005. You would buy physical servers, rent space in a data center, hire someone to rack and cable them, buy networking gear, and pay an electricity bill — all before serving a single visitor. If your site went viral, you would scramble to order more servers (weeks of lead time). If it flopped, you would own expensive metal doing nothing.
This is called running on-premises (or "on-prem"): you own and operate all the hardware yourself. It requires big upfront payments — known as capital expenditure (CapEx) — and forces you to guess your future capacity.
So what is cloud computing?
Cloud computing is the on-demand delivery of IT resources over the internet with pay-as-you-go pricing. Instead of buying servers, you rent exactly what you need from a provider like AWS and release it when you're done. You stop guessing capacity, stop maintaining hardware, and pay only for what you actually use — an operating expenditure (OpEx) model.
Owning servers is like buying a car: a big upfront cost, you pay for insurance and repairs, and it loses value even when parked. The cloud is like a ride-share: tap a button when you need a ride, pay per trip, and never think about oil changes. Need a truck today and a scooter tomorrow? Just request a different vehicle.
The definition, unpacked
- On-demand: get resources in minutes, not weeks — no procurement process.
- Delivery of IT resources: compute, storage, databases, networking, AI, and 200+ other services.
- Over the internet: access everything through the web, APIs, or command line from anywhere.
- Pay-as-you-go: no long-term contracts required; stop paying the moment you stop using a resource.
The three cloud service models
Cloud services come in layers, depending on how much you manage versus how much the provider manages. The exam expects you to recognize all three.
IaaS vs PaaS vs SaaS
| Model | What you get | You manage | AWS example |
|---|---|---|---|
| IaaS (Infrastructure as a Service) | Raw building blocks: virtual servers, storage, networks | OS, runtime, apps, data | Amazon EC2 |
| PaaS (Platform as a Service) | A managed platform to deploy code | Just your apps and data | AWS Elastic Beanstalk |
| SaaS (Software as a Service) | A complete, ready-to-use application | Only your usage and settings | Gmail, Salesforce, Amazon Chime |
Making pizza at home from scratch is on-prem. IaaS is buying a take-and-bake pizza (they supply it, you bake it). PaaS is delivery (you just eat, at your own table). SaaS is dining at the restaurant — everything is handled for you.
If a question says a customer wants the most control over the operating system, that points to IaaS (EC2). If they want to just upload code without managing servers, that's PaaS (Elastic Beanstalk). A finished app used through a browser is SaaS.
Which statement BEST defines cloud computing?