Joe Brockmeier

Recent Posts

A Practical Introduction to Docker Container Terminology

February 2018 – A completely revised and updated version of this article has been published.  See A Practical Introduction to Container Terminology. The update includes coverage of container technologies beyond docker, such as CRI-O, rkt, lxc/lxd, and as well information on the Open Container Initiative (OCI).



January 13th, 2016


When discussing an architecture for containerization, it’s important to have a solid grasp on the related vocabulary. One of the challenges people have is that many of the following terms are used interchangeably… often causing quite a bit of confusion for newcomers.

  • Container
  • Image
  • Container Image
  • Image Layer
  • Index
  • Registry
  • Repository
  • Tag
  • Base Image
  • Platform Image
  • Layer


The goal of this article is to clarify these terms, so that we can speak the same language and develop solutions and architectures leveraging the value of containers. Note that I am going to assume that you know how to run basic docker commands, but if you need a primer, I recommend starting with: A Practical Introduction to Docker Containers.

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A Practical Introduction to Docker Containers



Docker has quite an amount of buzz around it today because it makes so many things easy that were difficult with virtual machines.

Docker containers makes it easy for Developers, Systems Administrators, Architects, Consultants and others to quickly test a piece of software in a container; much quicker than a virtual machine, and using less resources. The average command in Docker takes under a second to complete.

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