"It works on my machine" used to be a common excuse when software failed on a server. Containers solve that problem by packaging an application with everything it needs.
What a container is
A container bundles:
- the application code,
- its runtime (for example Node.js or Python),
- libraries and settings.
It runs the same way on a developer laptop, a test server and in the cloud.
Containers vs. virtual machines
| Virtual machine | Container | |
|---|---|---|
| Includes | Full operating system | Only the app and dependencies |
| Start time | Minutes | Seconds |
| Size | Gigabytes | Megabytes |
| Density | Fewer per server | Many per server |
Both have their place; containers are lighter and faster for modern applications.
What Docker is
Docker is the most widely used tool to build and run containers. A simple text file (Dockerfile) describes how to build the container image.
Business benefits
- Consistency: fewer surprises between environments
- Faster deployments and easy rollbacks
- Scalability: start more containers when traffic grows
- Portability: move between cloud providers more easily
- Isolation: applications don't interfere with each other
Orchestration
When you run many containers, an orchestrator manages them: starting, stopping, scaling and healing. Kubernetes is the best known; simpler options include managed container services from cloud providers.
Security
Use trusted base images, scan images for vulnerabilities, keep them updated and don't store secrets inside images.
When containers make sense
- Web applications and APIs
- Microservices and multiple environments
- CI/CD pipelines and automated testing
For a simple website, managed hosting may be easier. We containerise applications where it adds value and choose the simplest platform to run them.