Cloud and service models¶

This morning you probably played a song on Spotify, opened Classroom and saved something to Google Drive. None of it ran on your phone, not really. Where was the song? Where is your homework right now? And who keeps the machine that stores it switched on at three in the morning?

The answer is "in the cloud", and it is less mysterious than it sounds. A hotel in Calvià that receives ten times more bookings in August than in January cannot buy ten servers for August and throw nine away in September. It rents. As a DAM developer, almost everything you build will end up running on somebody else's computer, so you need to know exactly what you are renting.

The cloud is renting from the utility¶

Cloud computing is on-demand access, over the network, to computing resources (servers, storage, databases, applications) that a provider shares among many customers, that can grow or shrink quickly, and that you pay for according to use.

In the city-builder game of this module, the cloud is renting water and electricity from a utility instead of building your own plant. You open the tap and pay the bill. The alternative is called on-premise: the company buys its own servers and keeps them in its own building.

The US standards institute NIST wrote the definition everyone quotes (SP 800-145, 2011). It lists five characteristics. A service that lacks them is not really cloud:

Back to the hotel. On-premise, it buys a server, puts it in an air-conditioned room and pays somebody to look after it: a big investment on day one, and if it falls short in August, bad luck. In the cloud there is no initial investment, it pays monthly according to use, and in August it asks for more capacity.

Three service models: IaaS, PaaS and SaaS¶

You can rent at three different heights. The higher you go, the more the provider does for you.

A service model says how much of the system the provider gives you ready-made, and how much is left for you to manage.

• IaaS (Infrastructure as a Service): you rent a virtual machine, a computer simulated by software on the provider's hardware. It is like renting an empty plot with water and power connected: you build the house.
• PaaS (Platform as a Service): you bring your code and the platform runs it. Like renting a furnished flat: you bring your things.
• SaaS (Software as a Service): you just use the application. Like staying in a hotel.

Who manages what¶

Stack the layers of any system from the building up to your data. For each model, mark what is the customer's job (C) and what is the provider's (P):

Look at the first row. Your data are always your responsibility, whatever the model. The higher you climb, the less administration you do, but the less control you have. Providers call this the shared responsibility model.

flowchart LR
    ON["<b>On-premise</b><br>(build your own<br>power station)"] --> I["<b>IaaS</b><br>(rent the plot<br>with power)"]
    I --> P["<b>PaaS</b><br>(rent a<br>furnished flat)"]
    P --> S["<b>SaaS</b><br>(stay in<br>a hotel)"]

GitHub Pages: a platform you can use today¶

GitHub Pages is a free GitHub service that publishes a static website (HTML, CSS and images that do not change per visitor) straight from a code repository.

You put the files in a repository; GitHub stores them, serves them to the world and keeps the servers running. You never see a server. That is the definition of PaaS, and you will use it all unit: in Deliverable 3 your group publishes its dossier as a GitHub Pages site.

Three facts to know before you start (checked on 25/10/2026 in GitHub's documentation):

In class: what level does it play at?¶

Part 1 · Classify real services. In the Classroom template:

Part 2 · Your first site on GitHub Pages.

If you cannot or do not want to open a GitHub account, make the page with Google Sites and your school account, and say in the sentence that Google Sites is SaaS, not PaaS. It does not affect your individual mark: in the deliverable, the website is group work.

Hand in on Classroom: the table of part 1 with its evidence, your three company systems and the link to your site. No generative AI: this activity is assessed (class work, 30%).

For your project¶

This lesson starts Deliverable 3 · Cloud architecture, due Monday 8 February 2027 at 23:59, with individual defences in session 14 that same day.

Key takeaways¶

• Cloud computing is renting computing resources on demand, over the network, shared, elastic and paid by use. It runs in real data centres. The opposite is on-premise.
• IaaS gives you machines, PaaS gives you a place to deploy your code, SaaS gives you the finished application.
• The higher the model, the less you administer and the less you control. Your data are always your responsibility (the shared responsibility model).
• End users mostly meet SaaS; developers live mostly in PaaS and IaaS.
• GitHub Pages publishes a static website from a repository: a PaaS you can use for free, with a public repository.

Quick check¶

You now know what you can rent. Next you will see who owns the power station, what the cloud is used for and how much the bill is: Deployment and functions.