Containers and virtual machines both let you run isolated workloads on shared hardware, but they isolate at different levels. Understanding the difference explains why a VPS (a virtual machine) running Docker (containers) is such a common and effective combination.

The architecture difference

Virtual machine: a hypervisor (KVM, VMware, Hyper-V) emulates hardware. Each VM boots its own operating system kernel, with its own drivers, init system and memory.

App A | App B         App C
Libs  | Libs          Libs
Guest OS (kernel)     Guest OS (kernel)
──────── Hypervisor ────────
        Host hardware

Container: processes on the host kernel, isolated with namespaces (what they can see) and cgroups (what they can use). No separate kernel; the image contains just the app and its userland libraries.

App A | App B | App C
Libs  | Libs  | Libs
── Container runtime ──
     Host OS kernel
     Host hardware

Comparison

Virtual machine Container
Isolation boundary Hardware virtualization, separate kernel Shared kernel, namespaces/cgroups
Startup time Tens of seconds Milliseconds to seconds
Size GBs (full OS) MBs to hundreds of MBs
Overhead Small with modern CPUs, but each VM needs OS memory Minimal
Density Dozens per host Hundreds or thousands per host
OS flexibility Any OS (Linux, Windows, BSD) Same kernel as the host (Linux containers on Linux)
Kernel customisation Yes No
Security isolation Strong Good, but a kernel bug can affect all containers
Portability VM images are large and hypervisor-specific Images run anywhere with a compatible runtime
Typical unit A server A process/service

Where virtual machines win

  • Strong isolation between tenants — why hosting providers sell VMs (VPS), not bare containers, to customers.
  • Different operating systems or kernels: Windows Server, BSD, custom Linux kernels, kernel modules (WireGuard, ZFS).
  • Full system control: firewall, init system, everything you’d do on a physical server.
  • Legacy applications that expect a complete OS.

Where containers win

  • Packaging: an image bundles the app with exactly the libraries it needs — “works on my machine” becomes “works everywhere”.
  • Speed and density: start, stop and replace services in seconds; run many on one server.
  • Reproducible deployments: the same image goes from CI to staging to production.
  • Microservices and scaling with orchestrators like Kubernetes or Docker Swarm.
  • Clean hosts: no dependency conflicts between apps (PHP 7 and PHP 8 side by side, different Node versions).

Better together: containers inside VMs

The common pattern is both:

  1. A KVM VPS gives you a dedicated, isolated server with its own kernel and firewall.
  2. Docker on that VPS runs your apps as containers — each with its own dependencies, easily updated and moved.

You get the strong isolation of a VM between you and other customers, plus the packaging and agility of containers for your own services. Cloud Kubernetes services work the same way: containers run on VMs.

This is also why a container-based VPS (OpenVZ, LXC) is often a poor fit for Docker — nesting containers inside containers is limited. See KVM vs OpenVZ vs LXC.

Security notes

Containers share the host kernel, so:

  • Keep the host kernel and Docker updated.
  • Don’t run untrusted containers with --privileged or the Docker socket mounted.
  • Run container processes as non-root users; consider rootless Docker or Podman.
  • Treat the host as the security boundary between workloads you don’t trust.

See Docker security best practices.

Which should you choose?

Need Choose
A server you control (web hosting, databases, VPN) VM (VPS)
Packaging and deploying apps consistently Containers
Running Windows or custom kernels VM
Many small services on one server Containers on a VM
Untrusted multi-tenant workloads VMs (or hardened sandboxes like gVisor, Kata Containers)

Start with what is a VPS and installing Docker on Ubuntu. Our Docker VPS plans run on KVM, so Docker, Compose and Kubernetes work without restrictions.

  • Docker
  • Virtualization
  • Containers