What is the difference between containerization and virtualization?

Virtualization emulates hardware, allowing multiple operating systems to run on a single physical server. Each virtual machine (VM) has its own OS, kernel, libraries, and applications. This provides strong isolation but requires significant resources (memory, CPU, disk space) for each VM.

Containerization operates at the OS level, sharing the OS kernel between applications. A container includes only the application, its dependencies, and libraries. This makes containers more lightweight, faster to start, and less resource-intensive than VMs. Isolation is achieved at the process and namespace level of the OS.

Here are the main differences:

Parameter	Virtualization	Containerization
Level of operation	Hardware	OS level
Isolation	OS and VM kernel	Processes and OS namespaces
Resources	High (per VM)	Low (shared kernel)
Speed	Slow VM startup	Fast container startup
Image size	Large (includes OS)	Small (application and dependencies only)
Portability	Requires VM compatibility	High (works on any host)

Example VM configuration:

// QEMU/KVM configuration file
[drive]
file=/var/lib/libvirt/images/my-vm.qcow2
if=virtio
bus=virtio
cache=none

[cpu]
type=host

[memory]
size=4g

Example Dockerfile for a container:

# Use base image
FROM ubuntu:20.04

# Install dependencies
RUN apt-get update && apt-get install -y nginx

# Copy application files
COPY html /var/www/html

# Expose port
EXPOSE 80

# Run application
CMD ["nginx", "-g", "daemon off;"]