What is Docker & Docker Container

Docker is a containerization platform that packages your application and all its dependencies together in the form of a Docker container to ensure that your application works seamlessly in any environment.

Docker Container is a standardized unit which can be created on the fly to deploy a particular application or environment. It could be an Ubuntu container, CentOs container, Docker etc…to full-fill the requirement from an operating system point of view. Also, it could be an application oriented container like CakePHP container or a Tomcat-Ubuntu container etc.

Let’s understand it with an example:

 A company needs to develop a Java Application. In order to do so the developer will setup an environment with tomcat server installed in it. Once the application is developed, it needs to be tested by the tester. Now the tester will again set up tomcat environment from the scratch to test the application. Docker Once the application testing is done, it will be deployed on the production server. Again the production needs an environment with tomcat installed on it, so that it can host the Java application. If you see the same tomcat environment setup is done thrice. There are some issues that I have listed below with this approach:

1) There is a loss of time and effort.

2) There could be a version mismatch in different setups i.e.

The developer & tester may have installed tomcat 7, however the system admin installed tomcat 9 on the production server.

Now, I will show you how Docker container can be used to prevent this loss.

In this case, the developer will create a tomcat docker image A Docker Image is nothing but a blueprint to deploy multiple containers of the same configurations using a base image like Ubuntu, which is already existing in Docker Hub Docker Hub has some base docker images available for free. Now this image can be used by the developer, the tester and the system admin to deploy the tomcat environment. This is how docker container solves the problem.

What is Docker Engine?

Now I will take you through Docker Engine which is the heart of the Docker system.

Docker Engine is simply the docker application that is installed on your host machine. It works like a client-server application which uses:

• A server which is a type of long-running program called a daemon process
• A command line interface (CLI) client
• REST API is used for communication between the CLI client and Docker Daemon

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