Docker : The Dev Container

What is Docker?

Docker is a containerization platform that packages applications into containers to run without any problem.

Before Docker/Containerization tool?

Before this for every application we use one whole server , which is so costly and difficult to maintain ,
so VMware solved that problem by using Virtual machines .

Even in Virtual Machines there are many flaws like,

• Dedicated OS for each application

• Not fast enough

• Dedicated storage

• Dedicated hardware & so on…..

Before Tools like Docker used in market , we have a Problem “IT works on my machine“.

Docker solved All the Problems.

Containers

Containers are collection of thing we need to run our applications.

It contains

• Base OS (mostly light weight OS)

• Infrastructure

• Container Engine

• Libraries needed to run the application

• Applications

Virtual Machines VS Containers

In Virtual Machines we need multiple OS to run multiple Application
But In Containers we just one OS for multiple Applications .

We use Container engine to run Multiple apps in single OS.

Installation

Windows

Install Docker Desktop + WSL from ( Windows OS ).

Mac

Install Docker Desktop from ( Mac OS ).

Linux

Install Docker Engine not Docker Desktop from ( Linux ).

Parts of Docker Desktop / Docker

Docker Runtime.

Docker Engine.

Docker Orchestration.

Docker Runtime

Basically allow us to Start/stop the container.

• runC (low level).

• containerD.

  • getting Data /internet.

  • manage runC.

Docker Engine

It contains Docker CLI , Rest API , DockerD(server) , Daemon .

Rest api is used to bridge between Sever and CLI .

Docker Orchestration

This manages the Containers .

Kubernetes is one of the orchestration tool.

Docker Images

Its a file that contains all the instructions to create a container for our applications.

We can Create Docker Images using Dockerfile.
We can Create Container using Docker Image.

Docker CLI commands

// docker run image-name
docker run hello-world

docker run - it will run the docker image if it is locally available or its download it from Docker Hub

docker images

docker images - it will return the available images locally

// docker pull image-name
docker pull ubuntu
//docker pull image-name:tag/version
docker pull ubuntu:16.01

docker pull - it will download the image from the Docker Hub
Note : if tag is not defined it will automatically download latest version

docker run -it ubunut

docker run -it ubuntu - its runs the image in interactive environment

docker ps
docker container ls

return all running containers

docker ps -a

return all the stopped containers

//docker rm container-id
docker rm 4f2304iua402j

docker rm - it will remove/delete the container

//docker rmi image-id
docker rmi 4239u020jasf9

docker rmi - it remove the docker image

Docker Layers

A Docker image is collection many files/layers

Each layers have a unique hash values as ID using “SHA256” representation.

If Two Docker images have same layer/file it will not download again from Docker Hub. it will use the already installed one for both images.

How to Create a Docker Image?

1. create a file named “ Dockerfile “ in the requires directory/folder.

2. write create instruction to run the container using Linux cmd’s.

3. Must declare a Base image(OS) in the file.

4. Write the instructions need to run the applications.

5. save the file.

//docker build -t image:tag/version path
docker build -t test-image:1.01 .

this command will build a docker image with file the mentioned directory , i mention “.” to use the same dir.

Is Docker needed for SDE roles in IT field today ?

Answer is Yes and No , because Docker is tool used by Devops people but in this modern time its will be useful to learn docker and Kubernetes to standout form the crowd while Appling for a job. Its not at all compulsory for Software Developer Role still today

Learning daily will make a big difference in a long run .
-rakeshraj .