Day 1Concepts⏱ 1.5h
What Is the Cloud, Really?
By the end of today you can
Explain the cloud to a non-technical friend, name the 6 advantages, tell IaaS / PaaS / SaaS apart, and estimate the monthly cost of a small server.
1. First principles: what problem does the cloud solve?
Every app needs three things: compute (a CPU to run code), storage (disks to keep data) and network (a way for users to reach it). Before the cloud, you had to buy these: servers, a room with cooling and power, a network connection, and people to babysit them.
That causes three painful problems:
- Guessing demand. Buy too few servers and the site crashes on launch day. Buy too many and money sits idle.
- Big upfront cost. Thousands of dollars before your first customer.
- Slow. Ordering hardware takes weeks.
Analogy: electricity
A hundred years ago, every factory ran its own power generator. Then power plants appeared and factories just plugged into the wall and paid for the units they used. Cloud computing is the power grid for computers. You don't own the generator. You plug in, use what you need, and get a bill.
So the cloud is: renting computing resources (servers, storage, databases, networking) over the internet from a provider's huge data centers, paying only for what you use, and getting them in minutes.
2. The 6 advantages of cloud (exam favourite)
| Advantage | Plain English | Real life |
|---|---|---|
| Trade fixed expense for variable expense | No big upfront purchase; pay as you go | Uber vs buying a car |
| Benefit from massive economies of scale | AWS buys in huge volume, so unit prices are lower than yours | Wholesale vs retail |
| Stop guessing capacity | Scale up or down as demand changes | Restaurant adding tables for a wedding |
| Increase speed and agility | Resources in minutes, so experiments are cheap | Test an idea this afternoon |
| Stop spending money running data centers | Focus on your product, not racks | Using a restaurant's kitchen instead of building one |
| Go global in minutes | Deploy near customers worldwide | Opening a branch in another country overnight |
3. Service models: how much do you manage?
Analogy: pizza as a service
On-premises = make pizza at home (you do everything). IaaS = rent a kitchen (you bring ingredients and cook). PaaS = takeaway (they cook, you pick the toppings). SaaS = dine in (just eat).
| Model | You manage | AWS example |
|---|---|---|
| IaaS (Infrastructure) | OS, runtime, app, data | EC2 |
| PaaS (Platform) | App and data only | Elastic Beanstalk, RDS |
| SaaS (Software) | Just use it | Amazon WorkMail, Gmail |
Deployment models: Public cloud (all in AWS), On-premises/private (your own data center), Hybrid (both connected).
4. Shared Responsibility Model (preview, you'll meet it every day)
AWS is responsible for security of the cloud (buildings, hardware, the virtualization layer). You are responsible for security in the cloud (your data, who has access, firewall rules, patching your OS on EC2).
Analogy: apartment buildingThe landlord secures the building entrance and the walls. You still have to lock your own door.
5. Lab (no AWS account needed yet): price a server
- Open the AWS Pricing Calculator (search "AWS Pricing Calculator"). You can use it without logging in.
- Add an Amazon EC2 estimate. Region: one close to you (e.g. Europe (Ireland) or Africa (Cape Town)). Linux, 1 instance, a small type like
t3.micro, 730 hours/month (always on). - Add a second estimate for the same server running only 8 hours a day on weekdays (~176 hours). Compare the totals.
- Write the two numbers in
aws-course/notes/day01.mdand one sentence: why does the cloud make the second option possible, when owning a server would not?
📸 Evidence: save a screenshot of your estimate as
evidence/day01-pricing-calculator.png6. Exam notes
Remember
- Cloud = on-demand delivery of IT resources over the internet with pay-as-you-go pricing.
- CapEx → OpEx is the headline benefit.
- Elasticity = scale out and in automatically with demand. Scalability = ability to handle growth.