4.5Virtualization & servers (basics)
The essentials in 30 seconds
- Virtualization runs several virtual machines (VMs) on the same physical machine, each with its own OS, via software called a hypervisor (Hyper-V, VMware, Proxmox).
- It optimises hardware and isolates services: a VM is created, cloned, moved and backed up like a file — it is also the technical basis of the cloud.
- VM = strong isolation (full OS per VM); container = light and fast (shares the host OS), ideal for deploying applications.
Running mini-case — Sofiane consolidates three servers onto one host
Sofiane, a systems administrator in a distribution SME in Algiers, inherits three old, underused physical servers: files, web and a test space. He consolidates them onto a single host fitted with a hypervisor: the "Files" VM running Windows Server, the "Web" VM running Linux, and a "Tests" VM that is isolated and disposable. The hardware is better used, a crash of "Tests" does not affect "Files", and each VM is backed up like a file. He then thinks about a service he could deploy in a container rather than a VM, lighter. He notes the reflex: consolidate, isolate, back up per VM.
Standalone case for this section: it returns in the course, the diagram, the script and the 48h challenge of section 4.5.
1. Several servers on one machine
Virtualization makes it possible to run several virtual machines (VMs) — each with its own OS — on a single physical machine. Software called a hypervisor (Hyper-V, VMware, Proxmox) shares the real hardware between the VMs, which believe they are alone on "their" computer.
2. Why it is everywhere
Before, one physical server = one role, often underused. Virtualization optimises the hardware (several VMs per server), isolates services (a problem on one VM does not affect the others) and makes operations easier: you create, clone, move, back up a VM like a file. It is also the technical basis of the cloud.
3. VMs and containers
Alongside VMs, containers (Docker) package an application and its dependencies more lightly, by sharing the host OS. VM = strong isolation (a full OS per VM); container = light and fast, ideal for deploying applications. The two coexist according to need.
🔎 Concrete example — 🔎 Concrete example — One physical server, three roles
Instead of three underused physical servers, Sofiane consolidates:
1 physical server + hypervisor
|-- VM « Files » (Windows Server)
|-- VM « Web » (Linux)
|-- VM « Tests » (isolated, disposable)
-> hardware optimised, services isolated, backup per VM
Reading : each VM is independent.
Lesson : a VM is backed up, cloned and moved like a file.Reading: each VM is independent; a crash of "Tests" does not affect "Files".
Lesson: a VM is backed up, cloned and moved like a file — huge flexibility.
Section vocabulary
- Virtualization
- Running several logical machines on the same physical hardware.
Simple example: Sofiane consolidates three servers into three VMs on one host.
What it is not: a single role per physical server, underused.
Reflex: several VMs on a host → virtualization.
- Virtual machine (VM)
- A complete software computer, with its own OS, isolated from the others.
Simple example: The "Files" VM running Windows Server runs alongside the "Web" VM.
What it is not: a mere application with no operating system.
Reflex: full OS isolated → VM.
- Hypervisor
- Software that creates and manages VMs by sharing the real hardware.
Simple example: Sofiane's host runs a hypervisor (Hyper-V, VMware, Proxmox).
What it is not: an antivirus that scans network traffic.
Reflex: sharing the hardware between VMs → hypervisor.
- Container
- A light package of an application and its dependencies, sharing the host OS.
Simple example: Sofiane deploys a web service in a container, lighter than a VM.
What it is not: a VM with a complete operating system.
Reflex: light and fast → container.
- Isolation
- Partitioning: a problem on one VM or container does not affect the others.
Simple example: The "Tests" VM crashes without touching the other services.
What it is not: services that share everything and fall together.
Reflex: a contained incident → isolation.
In practice — In practice — Designing a virtualization host
- List three services to host (files, web, tests), like Sofiane.
- Distribute them as VMs on the same host and justify the isolation.
- State how you would back up each VM.
- Say which of these services would benefit from being a container rather than a VM.
Step-by-step script — consolidating servers like Sofiane (5 min)
1) List the hosted services and spot the underused ones. 2) Choose a host with a hypervisor and create one VM per service (e.g. Files, Web, Tests). 3) Justify the isolation: a crash of "Tests" must not affect the others. 4) Plan the backup of each VM (like a file). 5) Identify a service that would benefit from moving to a container, lighter. 6) Keep in mind that all VMs share the same hardware.
Remember the basis: virtualization is also the technical foundation of the cloud — it returns in all the IaaS offerings seen in 4.1.
Copy-paste template — my consolidation sheet
Principle: several VMs on a physical machine, via a hypervisor
Host : Hyper-V / VMware / Proxmox
VM : a full OS each -> strong isolation
Benefit : hardware optimised + services isolated + backup per VM
Container: lighter, shares the host OS (deploy apps)
Warning : all VMs share the SAME hardware (host failure = all).Three underused servers
Sofiane consolidates files, web and tests into three VMs on a single host.
An isolated test
The "Tests" VM is disposable: it crashes without affecting production services.
A simple backup
Sofiane backs up each VM like a file, then restores it when needed.
A light application
To deploy and scale an application, Sofiane prefers a container to a VM.
✓ Best practices
- Consolidate several VMs per server (optimised hardware).
- Use isolation to partition services.
- Back up per VM (they are handled like files).
✗ Common pitfalls
- Overloading a host to the point of slowing everything down.
- Forgetting that all VMs share the same hardware.
- Confusing a VM (full OS) with a container (light).
Key takeaways
- Virtualization runs several VMs on a physical machine.
- The hypervisor shares the hardware; each VM has its own OS and is isolated.
- It optimises the hardware and makes backup, cloning and moving easier.
- Containers are a lighter alternative; it is the basis of the cloud.
48h challenge — apply it tomorrow
Like Sofiane, consolidate three services into VMs on the same host: name them (e.g. files, web, tests) and justify the isolation. State how you would back up each VM, then designate a service that would go well in a container. State the shared risk: a host failure takes down all the VMs.
- I can explain what a VM and a hypervisor are.
- I understand the benefit: optimisation, isolation, backup per VM.
- I place VMs and containers according to need.
Frequently asked questions
If all the VMs are on a single server, is that not risky?
The shared hardware is a common point: if the host goes down, all its VMs go down. You mitigate it with several hosts, high availability and backups; isolation protects against software failures, not against a hardware failure of the host.
VM or container, how do you choose?
A VM offers strong isolation with a full OS (ideal for varied servers); a container is light and fast (ideal for deploying and scaling applications). Many infrastructures combine both according to need.
What is a hypervisor?