4.1Understanding the cloud (SaaS, PaaS, IaaS)
The essentials in 30 seconds
- The cloud rents resources (servers, storage, applications) over the Internet, paid per use: you trade fixed costs (hardware, room, maintenance) for variable costs and flexibility.
- IaaS = you manage the OS and above; PaaS = the provider manages the foundation, you deploy your application; SaaS = turnkey application: three sliders between control and simplicity.
- The further up you go toward SaaS, the less you manage — and the less you control; the right model depends on the need, not on a trend, and vendor dependence must be watched.
Running mini-case — Sofiane sorts through the SME's cloud services
Sofiane, a systems administrator in a distribution SME in Algiers, inherits a table of services all labelled "cloud" by management. He decides to classify them by what the SME still manages. Messaging and office productivity are used turnkey: that is SaaS. A managed database where the team handles neither the OS nor updates: that is PaaS. A rented, "bare" server where he installs Windows Server and its roles himself: that is IaaS. He notes the administrator's reflex: "I look at who manages the OS", and he warns management about two points — the per-use cost climbs fast, and vendor dependence must be prepared for (reversibility).
Standalone case for this section: it returns in the course, the diagram, the script and the 48h challenge of section 4.1.
1. The cloud, someone else's computer
The cloud is renting computing power (servers, storage, applications) from a provider, accessible over the Internet and paid per use — rather than buying and maintaining your own servers. You trade fixed costs (hardware, room, maintenance) for variable costs and flexibility: scaling capacity up or down quickly. For Sofiane, a systems administrator, this shifts his job: fewer cables and racks, more portals, identities and policies.
2. IaaS, PaaS, SaaS: who manages what
Three models depending on what the provider takes care of. IaaS (infrastructure): you rent "bare" servers and storage, you manage the OS and everything above. PaaS (platform): you deploy your application, the provider manages the OS and the foundation. SaaS (software): you use a turnkey application (Microsoft 365, Gmail), you manage almost nothing. The mental rule: the further up you go, the less you manage… and the less you control.
3. Choosing by need (and watching the cost)
There is no "best" model: an SME often wants SaaS (nothing to maintain); a development team appreciates PaaS; a bespoke infrastructure need calls for IaaS. The administrator watches two pitfalls: vendor dependence (reversibility, where the data lives) and the per-use cost, which is not magically "cheaper" — it is different.
🔎 Concrete example — 🔎 Concrete example — Three needs, three models
Sofiane classifies three needs of the SME, one per model:
Small SME without IT -> SaaS: Microsoft 365, nothing to maintain
Team that codes -> PaaS: deploy the app, don't manage the OS
Bespoke need -> IaaS: rented servers, maximum control
Reading : the right model depends on what you want (not) to manage.
Lesson : you choose a slider between simplicity and control.Reading: the right model depends on what you want to manage or not — never on a trend.
Lesson: you slide a slider between simplicity (SaaS) and control (IaaS), watching per-use cost and dependence.
Section vocabulary
- Cloud
- Computing resources rented from a provider, over the Internet, paid per use.
Simple example: Sofiane's SME rents its office suite and servers instead of buying machines.
What it is not: a server bought and installed in a room at the SME.
Reflex: rented per use → cloud.
- IaaS
- Rented infrastructure (servers, storage); the customer manages the OS and above.
Simple example: Sofiane installs Windows Server on a rented "bare" server.
What it is not: a turnkey application consumed as is.
Reflex: you manage the OS → IaaS.
- PaaS
- Platform where you deploy your application; the provider manages the OS and the foundation.
Simple example: The team deploys its application without administering the operating system.
What it is not: a "bare" server where the whole OS is the customer's responsibility.
Reflex: you deploy the app, foundation managed → PaaS.
- SaaS
- Turnkey application used directly (Microsoft 365, Gmail).
Simple example: The SME's messaging and office suite, ready to use.
What it is not: a rented server where Sofiane manages every role.
Reflex: turnkey application → SaaS.
- Vendor dependence
- The difficulty of changing provider once installed with one (reversibility).
Simple example: Sofiane checks how to recover the data if the SME changes provider.
What it is not: a service you can leave without effort or cost.
Reflex: changing provider → reversibility.
In practice — In practice — Classifying the SME's cloud services
- List five services you know (Microsoft 365, a rented site, a managed database…), like Sofiane.
- Classify each as IaaS, PaaS or SaaS by who manages the OS.
- For each, note what the customer (the SME) still manages.
- Give one case where IaaS would be preferable to SaaS, and vice versa.
Step-by-step script — classifying a cloud service like Sofiane (4 min)
1) Take a cloud service in your organisation. 2) Ask the administrator's question: who manages the operating system? 3) If it is you → IaaS; if it is the provider but you deploy your application → PaaS; if you consume a turnkey application → SaaS. 4) For each service, note the per-use cost and the dependence risk. 5) Finally, classify the need, not the trend.
Keep this classification: sections 4.2 to 4.4 administer exactly the Microsoft 365 SaaS day to day.
Copy-paste template — my cloud classification sheet
Key question: who manages the OS?
me -> IaaS (rented bare servers)
the provider (I deploy the app) -> PaaS
no one on the client side -> SaaS (turnkey application)
Marker: the further up toward SaaS -> the less you manage, the less you control.
Watch: per-use cost + vendor dependence (reversibility).A turnkey service
Sofiane recognises a SaaS: the SME consumes messaging and office productivity without maintaining anything.
Deploying without managing the OS
The team deploys its application in PaaS: the provider looks after the foundation.
Maximum control
A bespoke need goes to IaaS: Sofiane manages the OS and the roles himself.
Always the same reflex
Sofiane classifies each service with a single question: who manages the OS?
✓ Best practices
- Choose the model by what you want to manage or not.
- Watch the per-use cost, which climbs fast.
- Anticipate vendor dependence (reversibility, data location).
✗ Common pitfalls
- Believing that "cloud = necessarily cheaper".
- Choosing IaaS when a SaaS would do (extra management overhead).
- Ignoring where the data is stored and under which jurisdiction.
Key takeaways
- The cloud rents resources over the Internet, paid per use.
- IaaS/PaaS/SaaS: the further up you go, the less you manage and the less you control.
- The right model depends on the need, not on a trend.
- Watch the per-use cost and vendor dependence.
48h challenge — apply it tomorrow
Like Sofiane, classify five cloud services in your organisation as IaaS, PaaS or SaaS, using the question "who manages the OS?". For each, write in one sentence what the SME still manages, then note a cost risk or vendor dependence.
- I can explain what the cloud is and what it changes.
- I tell IaaS, PaaS and SaaS apart by what you manage.
- I reason about the per-use cost and vendor dependence.
Frequently asked questions
Is the cloud cheaper than your own servers?
Not mechanically: it turns fixed costs into variable costs and removes hardware maintenance, but the per-use bill can exceed a purchase for a steady load. It is a model choice, not a guarantee of savings.
Is my data safe in the cloud?
The provider secures the infrastructure, but responsibility is shared: configuration, access and often backups remain on your side. Knowing where the data resides (and under which jurisdiction) is part of the choice.
What distinguishes SaaS from IaaS?