Docker Containers vs Virtual Machines: When to Use What
June 12, 2025
2 min read
Wesam Abousaid
English
dockerdevopscontainersvirtualizationinfrastructure
Containers vs Virtual Machines
Both containers and virtual machines (VMs) provide isolated environments, but they work differently. Let's explore when to use each.
How They Work
Virtual Machines:
- Run a complete operating system
- Include a hypervisor layer
- Each VM has its own kernel
- Hardware-level virtualization
Docker Containers:
- Share the host OS kernel
- Lightweight process isolation
- Use Linux namespaces and cgroups
- Application-level virtualization
Key Differences
| Aspect | Containers | Virtual Machines |
|---|---|---|
| Startup Time | Seconds | Minutes |
| Size | MBs | GBs |
| Performance | Near-native | Some overhead |
| Isolation | Process-level | Hardware-level |
| Security | Good | Better |
When to Use Containers
Containers are ideal for:
- Microservices: Lightweight and fast to deploy
- CI/CD Pipelines: Quick spin-up for testing
- Application Packaging: Consistent environments
- Scaling: Rapid horizontal scaling
Example use case:
FROM node:18-alpine
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
EXPOSE 3000
CMD ["npm", "start"]
When to Use Virtual Machines
VMs are better for:
- Strong Isolation: Running untrusted code
- Different OS Requirements: Windows on Linux host
- Legacy Applications: Full OS dependencies
- Regulatory Compliance: Strict isolation requirements
Hybrid Approach
Many organizations use both:
- VMs for infrastructure separation
- Containers within VMs for application deployment
- Kubernetes nodes as VMs running containers
Performance Considerations
# Container startup
docker run -d nginx # < 1 second
# VM startup
virsh start ubuntu-vm # 30-60 seconds
Conclusion
Choose containers for application deployment and microservices. Choose VMs when you need strong isolation or different operating systems. Often, the best solution combines both technologies.