What is Docker?

Docker packages an application and everything it needs to run code, libraries, settings, environment into a single unit called a container.

The problem it solves: software works on one machine but fails on another because of different operating system versions, library versions, or settings. This is the classic "it works on my machine" problem.

A Docker container includes everything the app depends on, so it runs identically on any machine with Docker installed.

Containers vs virtual machines: a virtual machine simulates an entire computer including its own OS. A container shares the host machine's OS kernel but isolates the app's environment. Containers are much smaller and faster to start.

Docker works closely with Kubernetes, which manages and scales containers across many servers.