Containers vs Virtual Machines
Two Ways to Isolate Software
A virtual machine emulates an entire computer - virtual CPU, virtual disk, and a full guest operating system with its own kernel. A container is just a group of ordinary processes on the host, isolated by two Linux kernel features:
- Namespaces - what the process can see (its own filesystem, network, process list, hostname)
- cgroups - what the process can use (CPU, memory, PIDs limits)
VM: App → Guest OS (full kernel) → Hypervisor → Host OS → Hardware
Container: App → Container runtime → Host OS (shared kernel) → Hardware| Virtual Machine | Container | |
|---|---|---|
| Boots in | minutes | milliseconds |
| Size | gigabytes | megabytes |
| Kernel | its own | shared with host |
| Isolation | very strong (hardware-level) | good (kernel-level) |
| Density per host | tens | hundreds |
Note: Containers share the host kernel. That's why they start instantly and stay tiny - and also why container security matters: a kernel exploit inside a container threatens the host. (More in the Security module.)
Tip: It's not either/or in real infrastructure - cloud providers typically run your containers inside VMs, combining VM isolation between customers with container speed for deployment.