Docker is a container management service. The keywords of Docker are develop, ship and run anywhere. The whole idea of Docker is for developers to easily develop applications, ship them into containers which can then be deployed anywhere. The initial release of Docker was in March 2013 and since then, it has become the buzzword for modern world development, especially in the face of Agile-based projects.

Docker is a platform for developers and sysadmins to build, run, and share applications with containers. The use of containers to deploy applications is called containerization. Containers are not new, but their use for easily deploying applications is.

Containerization is increasingly popular because containers are:

• Flexible: Even the most complex applications can be containerized.


• Lightweight: Containers leverage and share the host kernel, making them much more efficient in terms of system resources than virtual machines.


• Portable: You can build locally, deploy to the cloud, and run anywhere.


• Loosely coupled: Containers are highly self sufficient and encapsulated, allowing you to replace or upgrade one without disrupting others.


• Scalable: You can increase and automatically distribute container replicas across a datacenter.


• Secure: Containers apply aggressive constraints and isolations to processes without any configuration required on the part of the user.

Features of Docker

• Docker has the ability to reduce the size of development by providing a smaller footprint of the operating system via containers.


• With containers, it becomes easier for teams across different units, such as development, QA and Operations to work seamlessly across applications.


• You can deploy Docker containers anywhere, on any physical and virtual machines and even on the cloud.


• Since Docker containers are pretty lightweight, they are very easily scalable.

Components of Docker

Docker has the following components

• Docker for Mac− It allows one to run Docker containers on the Mac OS.


• Docker for Linux− It allows one to run Docker containers on the Linux OS.


• Docker for Windows− It allows one to run Docker containers on the Windows OS.


• Docker Engine− It is used for building Docker images and creating Docker containers.


• Docker Hub− This is the registry which is used to host various Docker images.


• Docker Compose− This is used to define applications using multiple Docker containers.

Docker Architecture



Layers

A Docker container image is structured in terms of “layers”. Process for building image

• Start with base image


• Load software desired


• Commit base image+software to form new image


• New image can then be base for more software Image is what is transferred

Loading of software

Images and containers

Fundamentally, a container is nothing but a running process, with some added encapsulation features applied to it in order to keep it isolated from the host and from other containers. One of the most important aspects of container isolation is that each container interacts with its own private filesystem; this filesystem is provided by a Docker image. An image includes everything needed to run an application - the code or binary, runtimes, dependencies, and any other filesystem objects required.

Containers and virtual machines

A container runs natively on Linux and shares the kernel of the host machine with other containers. It runs a discrete process, taking no more memory than any other executable, making it lightweight.

By contrast, a virtual machine (VM) runs a full-blown “guest” operating system with virtual access to host resources through a hypervisor. In general, VMs incur a lot of overhead beyond what is being consumed by your application logic.

Setting up a Docker environment

Download and install Docker Desktop

Docker Desktop is an easy-to-install application for your Mac or Windows environment that enables you to start coding and containerizing in minutes. Docker Desktop includes everything you need to build, run, and share containerized applications right from your machine.

Test Docker version

After one have successfully installed Docker Desktop, open a terminal and run docker --version to check the version of Docker installed on your machine.



Test Docker installation

Test that your installation works by running the hello-world Docker image



Run docker image ls to list the hello-world image that you downloaded to your machine.

List the hello-world container (spawned by the image) which exits after displaying its message. If it is still running, you do not need the --all option:



At this point, one installed Docker Desktop on his or her development machine, and ran a quick test to ensure one is set up to build and run his or her first containerized application