What is Docker?

Docker is an open-source platform that automates the deployment, scaling, and management of applications using containerization technology. It was released in 2013 by Docker, Inc. and quickly became the industry standard for packaging and running applications in lightweight, isolated environments called containers. Docker enables developers to package an application together with all its dependencies — code, runtime, system libraries, environment variables, and configuration — into a single portable unit. This container can then run consistently on any machine that has Docker installed, regardless of the underlying operating system or infrastructure. The famous promise: "works on my machine" becomes "works on every machine." Docker is built on Linux kernel features: namespaces (process isolation), cgroups (resource limiting), and union file systems (layered image storage). Docker is used extensively in development, CI/CD pipelines, and production deployments, and forms the foundation for container orchestration with Kubernetes.