What is Docker ?

• Wikipedia defines Docker as

Docker is a computer program that performs operating-system-level virtualization, also known as "containerization".It was first released in 2013 and is developed by Docker, Inc

Docker is used to run software packages called "containers". Containers are isolated from each other and bundle their own application, tools, 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 often created by combining and modifying standard images downloaded from public repositories.

• Docker Inc. defines as

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

• and there are many more definitions

Understanding what is docker?

To understand docker, it is essential that we understand what a container is, So lets try to understand what is a container. To make this process simple by considering an application deployment in Virtual Machines and Docker Platform

• I would be taking an example of need for deploying two applications
  • runs on tomcat
  • runs on node js

Virtual Machine

• Lets Understand how virtual machines can achieve the above mentioned application deployments

• First we need to have a physical/cloud based infrastructure, on top of it we would be installing the host operating system, then we would install hypervisors like Vmware, Virtual Box, Hyper-V etc.

• Then we would create two different virtual machines. In each virtual machine we would

  • install operating system
  • install necessary softwares
  • allocate memory etc

Docker

• Lets Understand how docker containers can achieve the above mentioned application deployments

• First we need to have a physical/cloud based infrastructure, on top of it we would be installing the host operating system, then we would install docker.

• Docker will create two different isolated areas on your OS where we can run our applications. By the way this isolated area is called as Container

• Unlike Virtual Machine, there is no need to install host os , we can directly deploy our applications.

• Your applications will still be isolated, as they get the different virtual ip address, different memory spaces etc

• Important Docker is used to isolate individual applications not entire systems, whereas to isolate entire system we would go for hypervisors & create Virtual Machines

Now you can have a look at above definitions & things should be clear.