Docker: Containerisation Explained for Clients
Docker is the most widely used containerisation technology. It packages application code, runtime, libraries, and configuration into a portable, self-contained image that runs consistently across any environment — development laptops, test servers, and production cloud infrastructure.
The Core Problem Docker Solves
The classic problem: "it works on my machine but not in production." Before containers, applications depended on specific versions of programming language runtimes, system libraries, and environment configuration — all of which could differ between environments. Docker packages everything the application needs, eliminating environment-specific configuration drift.
Key Concepts
- Image: A read-only snapshot of the application and its environment — defined by a Dockerfile and built reproducibly
- Container: A running instance of an image — isolated, ephemeral, and disposable
- Dockerfile: A script defining how to build the image — the exact operating system base, packages to install, code to copy, and command to run
- Docker registry: A storage service for images — Docker Hub, Amazon ECR, Google Artifact Registry
- Docker Compose: A tool for defining and running multi-container applications locally — defining web server, database, and cache as a single local development environment
How We Use Docker
Every application we build is containerised. This means:
- Identical local development and production environments
- Reproducible builds — the same image is deployed to staging and production
- Fast deployment and rollback — deploy a new image, revert to the previous one if needed
- Efficient resource utilisation on cloud infrastructure