Docker

Docker uses operating-system-level virtualization to develop and deliver software in packages called containers

The software that hosts the containers is called Docker Engine

Docker Feature

Containers are isolated from each other and bundle their own software, libraries and configuration files, they can communicate with each other through well-defined channels.

All containers are run by a single operating-system kernel and are thus more lightweight than virtual machines.

Containers are created from images that specify their precise contents. Images are portable.

Docker Technology

Building on top of facilities provided by the Linux kernel (primarily cgroups and namespaces), a Docker container, unlike a virtual machine, does not require or include a separate operating system. Instead, it relies on the kernel's functionality and uses resource isolation for CPU and memory,and separate namespaces to isolate the application’s view of the operating system. Docker accesses the Linux kernel’s virtualization features either directly using the libcontainer library, or indirectly via libvirt, LXC (Linux Containers) or systemd-nspawn.

Docker Terminology

• Docker daemon

  The Docker daemon, called dockerd, is a persistent process that manages Docker containers and handles container objects. The Docker client program, called docker, provides a command-line interface that allows users to interact with Docker daemons

• Docker container

  A Docker container is a standardized, encapsulated environment that runs applications. A container is managed using the Docker API or CLI

• Docker image

  A Docker image is a read-only template used to build containers. Images are used to store and ship applications

• Docker service

  A Docker service allows containers to be scaled across multiple Docker daemons. The result is known as a swarm, a set of cooperating daemons that communicate through the Docker API

• Docker registry

  A Docker registry is a repository for Docker images. Docker clients connect to registries to download (“pull”) images for use or upload (“push”) images that they have built. Registries can be public or private. Two main public registries are Docker Hub and Docker Cloud

• Docker Compose

  Docker Compose is a tool for defining and running multi-container Docker applications. It uses YAML files to configure the application’s services and performs the creation and start-up process of all the containers with a single command

• Docker Swarm

  Docker Swarm provides native clustering functionality for Docker containers, which turns a group of Docker engines into a single virtual Docker engine. In Docker 1.12 and higher, Swarm mode is integrated with Docker Engine