Two lessons later in this curriculum — Building a Testing Lab with Docker and Kali and Getting Started with Kali Linux — jump straight into spinning up containers and tools. Both quietly assume you already understand why you run a vulnerable target in an isolated sandbox and how you keep it from touching anything you do not own. This lesson is the gentle precursor that supplies that discipline: it explains the safe-isolation habit, so the applied lessons can put it to work.
There is no attacking here — only the practice that makes everything that follows legal and safe. Let us start with the two ways you isolate software: virtual machines and containers.
What a virtual machine is
A virtual machine (VM) is a complete computer — its own operating system, disk, and virtual hardware — running as software inside your real computer. The program that creates and runs VMs is the hypervisor (VirtualBox, VMware, Hyper-V, KVM). Two words you will see everywhere:
- Host — your physical machine and the hypervisor on it.
- Guest — the operating system running inside the VM.
One host can run several guests at once, each believing it has its own hardware. The point that matters for us: a guest is isolated from the host and from other guests. What happens inside one VM stays inside it — which is exactly why a VM is the right place to run something deliberately broken.
What a container is, and how it differs
A container (Docker is the common tool) also packages and isolates software, but it does not ship a whole operating system. Many containers share the host's kernel and isolate only the application and its dependencies.
- A VM virtualises the hardware and runs a full guest OS — heavier (gigabytes, slow to boot) but strongly isolated.
- A container virtualises the OS environment and shares the host kernel — lightweight (megabytes, starts in seconds) but more weakly isolated.
In a practice lab you often use both: a VM for your attacker box (Kali) and a container for the vulnerable target (NovaCart runs as a single docker run command). The next lesson builds exactly this.
When you are ready, send Continue, and we will cover the two habits that keep a lab safe — snapshots and the right network mode — and the one rule that makes practice legal.