What is docker?

What is Docker?

Docker is a containerization platform used to develop, ship, and run containers. Docker doesn't use a hypervisor, and you can run Docker on your desktop or laptop if you're developing and testing applications. The desktop version of Docker supports Linux, Windows, and macOS. For production systems, Docker is available for server environments, including many variants of Linux and Microsoft Windows Server 2016 and above. Many clouds, including Azure, support Docker.

Docker architecture

The Docker platform consists of several components that we use to build, run, and manage our containerized applications.

Docker Engine

The Docker Engine consists of several components configured as a client-server implementation where the client and server run simultaneously on the same host. The client communicates with the server using a REST API, which enables the client to also communicate with a remote server instance.

Some arrows show communication between the Docker Server, running Containers, and stored container images. These arrows indicate how the Docker server loads stored container images and manage running containers.

The Docker client

There are two alternatives for Docker client: A command-line application named docker or a Graphical User Interface (GUI) based application called Docker Desktop. Both the CLI and Docker Desktop interact with a Docker server. The docker commands from the CLI or Docker Desktop use the Docker REST API to send instructions to either a local or remote server and functions as the primary interface we use to manage our containers.

The Docker server

The Docker server is a daemon named dockerd. The dockerd daemon responds to requests from the client via the Docker REST API and can interact with other daemons. The Docker server is also responsible for tracking the lifecycle of our containers.

Docker objects

There are several objects that you'll create and configure to support your container deployments. These include networks, storage volumes, plugins, and other service objects. We won't cover all of these objects here, but it's good to keep in mind that these objects are items that we can create and deploy as needed.

Docker Hub

Docker Hub is a Software as a Service (SaaS) Docker container registry. Docker registries are repositories that we use to store and distribute the container images we create. Docker Hub is the default public registry Docker uses for image management.

Keep in mind that you can create and use a private Docker registry or use one of the many cloud provider options available. For example, you can use Azure Container Registry to store container images to use in several Azure container-enabled services.

Trivia

The decision to use a whale in the logo and branding was inspired by Moby-Dick, the famous novel by Herman Melville. In the book, the character "Moby Dick" is a massive whale that represents something challenging to conquer, akin to the complexity of managing software infrastructure!