What is Docker and why use it?
What Docker Does
Docker uses OS-level virtualization to create containers from images. An image is a read-only template with your code, runtime, libraries, and settings. When you run an image, it becomes a container: an isolated process on the host machine.
Containers share the host OS kernel, so they start quickly and use fewer resources than virtual machines. Docker provides tools to build images (Dockerfile), run containers (docker run), and share images via registries like Docker Hub.
- Consistent environment from dev to production
- Fast startup and low overhead
- Easy dependency packaging
- Portable across clouds and laptops
- Supports microservices architecture
Why Teams Use It
Docker solves the 'it works on my machine' problem by bundling everything the app needs. You can test the exact same image locally that will run in production. This reduces deployment surprises and speeds up onboarding.
It also enables efficient scaling and orchestration. Tools like Kubernetes and Docker Swarm manage many containers across servers. For CI/CD, Docker lets you run tests in clean, reproducible environments.
Common mistakes
- Thinking Docker is a virtual machine; containers are not full VMs and share the host kernel.
- Building huge images by including unnecessary files, which slows down deployment.
- Running containers as root by default, which is a security risk.
