Containers vs Virtual Machines

Containers share the host operating system kernel while virtual machines each run a full guest OS, making containers lighter and faster.

People often confuse containers with virtual machines. Both isolate applications, but they work very differently.

Virtual machines

A virtual machine (VM) runs a full guest operating system on top of a hypervisor. Each VM includes its own OS kernel, which makes it heavy — often measured in gigabytes — and slow to boot.

Containers

A container shares the host machine's kernel and only packages the application and its libraries. This makes containers tiny (often megabytes) and able to start in a fraction of a second.

Diagram comparing virtual machine architecture with container architectureVirtual MachinesContainersInfrastructureHost OSHypervisorApp AGuest OSApp BGuest OSInfrastructureHost OSDocker EngineApp AApp BApp C
VMs each carry a full guest OS; containers share the host OS through the Docker Engine.

When to use which

Use containers for packaging and shipping applications. Use VMs when you need full OS isolation or to run a different kernel. In practice, containers often run inside VMs in the cloud.

Example

Example · bash
# See how little space a small image takes
docker pull alpine
docker images alpine
# REPOSITORY   TAG      SIZE
# alpine       latest   ~7MB

When to use it

  • A team migrates from VMs to Docker containers to cut startup time from minutes to milliseconds for each microservice.
  • A hosting company uses containers instead of VMs to run 10x more isolated workloads on the same physical hardware.
  • Developers choose containers over VMs for local development because containers share the host OS kernel and use far less RAM.

More examples

Start a lightweight container

Shows a container booting nearly instantly by sharing the host kernel, unlike a VM that boots a full OS.

Example · bash
# Starts in milliseconds, uses ~5 MB RAM
docker run --rm alpine echo 'Container started'

Check container resource usage

Displays real-time CPU and memory usage, demonstrating the minimal overhead of a container vs a VM.

Example · bash
docker run -d --name myapp nginx
docker stats myapp --no-stream

Run multiple isolated containers

Launches two different web servers side by side on the same host, each isolated without needing separate OS instances.

Example · bash
docker run -d --name app1 nginx
docker run -d --name app2 httpd
docker ps

Related

docker introdocker architecture

Discussion

  • Be the first to comment on this lesson.