Summary
Docker is the most widely adopted container platform, providing tools to build, ship, and run applications in lightweight, isolated containers that include everything needed to run the software.
What is Docker?
Docker packages an application and all its dependencies—runtime, libraries, configuration—into a container image. This image runs identically on a developer's laptop, a CI server, and a production cloud instance, eliminating the "works on my machine" problem.
The Docker daemon manages containers on the host, the Docker CLI provides the user interface, and Dockerfiles define the steps to build an image. Images are layered: each instruction in a Dockerfile adds a read-only layer, and layers are shared across images to reduce storage and transfer costs.
Docker Hub and private registries store and distribute images. Docker Compose extends the single-container model to multi-container applications, while Kubernetes uses container images as its deployment unit for production orchestration.
Why is Docker relevant?
- Consistency: The same image runs in development, testing, and production without modification
- Isolation: Containers share the host kernel but are isolated from each other and the host
- Speed: Containers start in milliseconds compared to minutes for virtual machines
- Ecosystem: The OCI image standard means Docker images run on any compliant runtime