A list of terms used around the Docker project.


aufs (advanced multi layered unification filesystem) is a Linux filesystem that Docker supports as a storage backend. It implements the union mount for Linux file systems.

Base image

An image that has no parent is a base image.


boot2docker is a lightweight Linux distribution made specifically to run Docker containers. The boot2docker management tool for Mac and Windows was deprecated and replaced by docker-machine which you can install with the Docker Toolbox.


btrfs (B-tree file system) is a Linux filesystem that Docker supports as a storage backend. It is a copy-on-write filesystem.


build is the process of building Docker images using a Dockerfile. The build uses a Dockerfile and a “context”. The context is the set of files in the directory in which the image is built.


cgroups is a Linux kernel feature that limits, accounts for, and isolates the resource usage (CPU, memory, disk I/O, network, etc.) of a collection of processes. Docker relies on cgroups to control and isolate resource limits.

Also known as : control groups


Compose is a tool for defining and running complex applications with Docker. With compose, you define a multi-container application in a single file, then spin your application up in a single command which does everything that needs to be done to get it running.

Also known as : docker-compose, fig


A container is a runtime instance of a docker image.

A Docker container consists of

  • A Docker image
  • Execution environment
  • A standard set of instructions

The concept is borrowed from Shipping Containers, which define a standard to ship goods globally. Docker defines a standard to ship software.

data volume

A data volume is a specially-designated directory within one or more containers that bypasses the Union File System. Data volumes are designed to persist data, independent of the container's life cycle. Docker therefore never automatically delete volumes when you remove a container, nor will it “garbage collect” volumes that are no longer referenced by a container.


The term Docker can refer to

  • The Docker project as a whole, which is a platform for developers and sysadmins to develop, ship, and run applications
  • The docker daemon process running on the host which manages images and containers

Docker Hub

The Docker Hub is a centralized resource for working with Docker and its components. It provides the following services:

  • Docker image hosting
  • User authentication
  • Automated image builds and work-flow tools such as build triggers and web hooks
  • Integration with GitHub and Bitbucket


A Dockerfile is a text document that contains all the commands you would normally execute manually in order to build a Docker image. Docker can build images automatically by reading the instructions from a Dockerfile.


A file system is the method an operating system uses to name files and assign them locations for efficient storage and retrieval.

Examples :

  • Linux : ext4, aufs, btrfs, zfs
  • Windows : NTFS
  • OS X : HFS+


Docker images are the basis of containers. An Image is an ordered collection of root filesystem changes and the corresponding execution parameters for use within a container runtime. An image typically contains a union of layered filesystems stacked on top of each other. An image does not have state and it never changes.


libcontainer provides a native Go implementation for creating containers with namespaces, cgroups, capabilities, and filesystem access controls. It allows you to manage the lifecycle of the container performing additional operations after the container is created.


libnetwork provides a native Go implementation for creating and managing container network namespaces and other network resources. It manage the networking lifecycle of the container performing additional operations after the container is created.


links provide a legacy interface to connect Docker containers running on the same host to each other without exposing the hosts' network ports. Use the Docker networks feature instead.


Machine is a Docker tool which makes it really easy to create Docker hosts on your computer, on cloud providers and inside your own data center. It creates servers, installs Docker on them, then configures the Docker client to talk to them.

Also known as : docker-machine

overlay network driver

Overlay network driver provides out of the box multi-host network connectivity for docker containers in a cluster.

overlay storage driver

OverlayFS is a filesystem service for Linux which implements a union mount for other file systems. It is supported by the Docker daemon as a storage driver.


A Registry is a hosted service containing repositories of images which responds to the Registry API.

The default registry can be accessed using a browser at Docker Hub or using the docker search command.


A repository is a set of Docker images. A repository can be shared by pushing it to a registry server. The different images in the repository can be labeled using tags.

Here is an example of the shared nginx repository and its tags


Swarm is a native clustering tool for Docker. Swarm pools together several Docker hosts and exposes them as a single virtual Docker host. It serves the standard Docker API, so any tool that already works with Docker can now transparently scale up to multiple hosts.

Also known as : docker-swarm


A tag is a label applied to a Docker image in a repository. tags are how various images in a repository are distinguished from each other.

Note : This label is not related to the key=value labels set for docker daemon


Docker Toolbox is the installer for Mac and Windows users.

Union file system

Union file systems, or UnionFS, are file systems that operate by creating layers, making them very lightweight and fast. Docker uses union file systems to provide the building blocks for containers.

Virtual Machine

A Virtual Machine is a program that emulates a complete computer and imitates dedicated hardware. It shares physical hardware resources with other users but isolates the operating system. The end user has the same experience on a Virtual Machine as they would have on dedicated hardware.

Compared to to containers, a Virtual Machine is heavier to run, provides more isolation, gets its own set of resources and does minimal sharing.

Also known as : VM