A Quick Guide to Docker Terminology

New to Docker and wondering what the different terms in the container ecosystem mean? Keep reading for a primer on Docker terminology.

Docker terminology may not be as confusing as, say, words related to AWS, which loves to make up acronyms for everything under the sun.

But using Docker does require you to be familiar with a variety of terms, which don’t always mean the same thing within the context of Docker that they do elsewhere. Those terms include:

  • Build: When people talk about building Docker containers, they usually mean the process of creating a container image. That’s different from other technical contexts, where build usually refers to the process of compiling source code.
  • Container: An instance of an application that is created based on a container image (which is in turn based on an application). It’s important to understand that a container is not the application itself; it’s just a copy of it. As a result, anything you do to a container won’t result in permanent change to the application.
  • Docker: This term is confusing because it refers to both Docker the project and Docker Inc., the company that leads Docker development. These are not the same entities. It’s worth keeping that in mind.
  • Docker Engine: The system that lets you create and run Docker containers.
  • Microservice: A service that provides part of the functionality required to run an application, such as data storage.
  • Node: A machine that hosts Docker Engine. A node can be a physical or a virtual machine.
  • Pull: What you do when you download a container image from a registry into a local cache so you can start containers based on the image.
  • Registry: A place where container images are stored. People sometimes use the term registry interchangeably with repository, but that’s not quite right. A single registry can contain multiple repositories of container images.

The list could go on. For a more complete version, check out Docker’s glossary—but bear in mind that it is very Docker-centric. It does not mention Kubernetes, for example, which is sign of how the container universe is being split between its Docker Inc. and Kubernetes/CoreOS/Red Hat halves. But that is a story for a different day.

Christopher Tozzi

Christopher Tozzi has covered technology and business news for nearly a decade, specializing in open source, containers, big data, networking and security. He is currently Senior Editor and DevOps Analyst with Fixate.io and Sweetcode.io.

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