Cloud Computing Basics
IaaS, PaaS, and SaaS, and why renting compute changed how software gets built.
On this page5 sections
Cloud computing means renting someone else's computers - over the internet, by the hour or by the second - instead of buying and racking your own hardware.
The three service models
| Model | What the provider manages | What you still manage | Example |
|---|---|---|---|
| IaaS (Infrastructure) | Physical servers, networking, virtualization | OS, runtime, your app | A virtual machine |
| PaaS (Platform) | + the OS and runtime | Just your application code | A managed app platform |
| SaaS (Software) | Everything, including the app | Just your data and settings | Gmail, Slack |
Each layer up the stack trades flexibility for less to manage. DevOps work tends to live mostly in the IaaS layer and the tooling that sits just above it.
Why it changed everything
Before the cloud, getting a new server meant ordering hardware, waiting days or weeks for it to arrive, and racking it yourself. Three properties flipped that:
- On-demand - a new server exists in seconds, not weeks.
- Elastic - scale from one instance to a thousand and back, automatically, as load changes.
- Pay-as-you-go - pay for what you used this hour, not what you guessed you'd need this year.
Regions and Availability Zones
Every major provider splits the world into regions (e.g. "US East", "EU West"), and each region into multiple Availability Zones - physically separate data centers with independent power and networking.
Spreading a service across AZs within a region is the cheapest insurance against "one data center had a bad day" taking your whole application down with it.
Shared responsibility
The provider secures the cloud itself (physical security, the hypervisor, their network). You're still responsible for securing what you put in the cloud - your data, your access controls, your configuration. A misconfigured storage bucket is on you, not them.
Try it
curl -I https://api.example-cloud.com
When you're ready, hit Mark complete and move to the next lesson.
Challenge
Send a HEAD request to https://api.example-cloud.com to check the cloud provider's API is reachable, without downloading the body.
Want to experiment first? Try things in the practice terminal (opens in a new tab), then enter the command that solves the task here.
Quiz
Lock in the concepts. Score at least 80% to mark the lesson complete.
Done with this one?
Skipped the challenge? You can mark the lesson complete by hand.