Cloud & DevOps
Docker is an open-source platform that enables developers to build, package, and distribute applications as portable containers, each bundling the application code with its exact runtime environment.
Docker introduced a standardised way to define container images via a Dockerfile — a plain-text script specifying the base OS, dependencies, environment variables, and startup command — which can be version-controlled alongside application code. The Docker Hub registry hosts millions of pre-built images for databases, web servers, and programming language runtimes that teams can pull and customise rather than building from scratch. Docker Compose extends this with a declarative YAML format for defining multi-container applications (e.g., an app server + PostgreSQL + Redis) that start up together with a single command. While Docker excels at the build-and-run layer, Kubernetes or Docker Swarm is typically added to orchestrate containers across multiple machines in production.
Example
A backend developer runs docker-compose up to start a local environment with their Node.js API, PostgreSQL database, and Redis cache — all isolated from the host system and ready in 30 seconds.
Related terms
Kubernetes
Kubernetes is an open-source container orchestration platform that automates the deployment, scaling, load balancing, self-healing, and management of containerised applications across clusters of machines.
Containerization
Containerization is a lightweight virtualisation technique that packages an application and all its dependencies — libraries, configuration, and runtime — into a portable, isolated container that runs consistently across any environment.
CI/CD (Continuous Integration / Continuous Delivery)
CI/CD is a DevOps practice in which code changes are automatically built, tested, and deployed through a pipeline, enabling teams to deliver software updates rapidly and reliably.
Microservices
Microservices is an architectural style in which a large application is built as a collection of small, independently deployable services, each responsible for a specific business capability and communicating via APIs.
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