Docker Tutorial for Beginners Part-I

This article was published as a part of the Data Science Blogathon.

Introduction

In this article, we are going to introduce you to Docker tutorial and will further learn the basic commands as well from installing docker, Pulling images from the hub to running Linux machines in docker.

Let’s first understand the challenges we face while deploying an application or server and then how docker solved this problem

When we run and deploy any application or a machine learning model or application or a database or some third parties package they need some libraries and dependencies, Working on multiple applications requires different versions of dependencies can lead to a dependencies conflict.

This problem could be solved either by using separate machines or by packaging all the dependencies with their application.

What is Docker?

Docker is a containerization and manager tool, Docker means Develop, Ship, and Run anywhere no matter what operating system we are using and the environment. Docker is a kind of isolated space where an application runs by using system resources.

Note: In this article, I have used the word Capsule for the word Container. Containers are often called Capsules.

Features of Docker

Docker is a full package solution for an app migration. It comes with the following features:

• Containers are light and flexible compared to running an application on virtual machines. It doesn’t depend on the version of the Operating System
• It can be easily deployed to the cloud server or local servers with ease.
• easily scalable. Supports Scaling with ease.

Docker Components

Docker is made up of 3 components, these components are responsible for their own tasks from building, and running to creating capsules.

• Docker Engine ( Used for building and creating docker containers).
• Docker Hub ( This is a place where you can host your docker images).
• Docker Compose ( It defines applications )

Docker Architecture

Docker Architecture consists of the Units that the docker is made up of these units are responsible for their own pre-defined tasks.

• Docker CLI ( Command Line Interface)
• Rest API ( connects docker daemon)
• Docker Daemon ( Responsible for Objects, Images, Containers, Engines, etc.)

After 2015 docker was redesigned according to standardization and it must support Runtime Specification and Image Specification.

• Runtime Specification defines the lifecycle of the capsule technology.
• Earlier Docker Daemon was responsible for all the processes in docker but after the Standardization runc (Container Runtime) is responsible for spinning the Image. In Container orchestration tools like Kubernetes, we only need to install a container runtime to spin a container on its pod.
• shim runc + shim makes docker daemon less.Shim monitors the running capsules.

Docker Setup

The complexity of docker installation depends on the operating system. Use this link for installing docker in your system.

For this article, I’ll be using docker on my Linux machine.

After installing verify if docker is installed by typing the code

$ docker --version

Managing Docker as a Service

Getting the Status of Docker-Engine if it’s up or not.

$ systemctl status docker

As you see our docker engine is up and active. It can be easily stopped by the command

# stops the docker engine
$ systemctl stop docker
#Starts the docker engine
$ systemctl start docker

Starting the docker in debug mode if the docker service is facing errors.

$ sudo dockerd --debug

Docker CLI & Deploy Your first Container

A docker image contains all the dependencies, source files, and tools needed to run an application. A Docker image is a source file that creates a capsule.

A capsule is a running instance created by a docker image.

Docker Hello-world

Docker hello-world is an image file that makes a docker capsule and that prints hello world.

docker run hello-world

It will first check the hello-world image file in its local registry. If not found, it pulls the image file from the docker hub ( default public registry) and runs the capsule.

Printing All the Containers

List only already running capsules

docker ps

List down all the docker-capsules

docker ps -a

The highlighted part with the yellow colour is the Capsule ID/Container ID, and whenever we want to select a specific capsule, we use its Container ID.

Note: We don’t need to write the whole container-ID, if the container-ID is unique we can only provide its first few starting characters.

docker rm 70

This command will remove the Capsules whose container ID starts with 70.

List Down All the Images

This lists all the docker images available in our local registry.

docker images

Deleting an Image

If you want to delete an image from our local repository, we need to execute the following commands.

docker image rm ID_OF_CONTAINER
#---OR----
docker image rm Image_Name

Pulling Image from Docker Hub

Any Image file available on the docker hub or from other sources can be pulled in the local docker registry using the pull command.

The command docker pull only download the image file; it won’t make any capsule using the image file unless we ask docker to do that.

Docker Inspect

The Docker inspect is a powerful command that lets us examine a container’s information, exposed ports, and network properties.

Inspect command can be used to inspect an image file or a capsule.

#Inspecting docker image
docker image inspect IMAGE_ID

# Docker Container Inspect
docker container inspect ID_OF_CONTAINER
# --- OR----
docker inspect ID_OF_CONTAINER

Running Ubuntu in Docker

To run a Linux as a docker capsule, we first need to pull the ubuntu image file.

docker pull ubuntu
docker images

Now we have an ubuntu image file in our local registry. It’s time to spin the capsule using the image file.

docker run -it ubuntu

• Here -it signifies that we want our capsule to run in interactive mode. It will wait for our response.
• We can run the Linux commands now to check if our Linux capsule is up or not.
• Ubuntu uses the command “/bin/bash” to enter the capsule. We can use the terminal of ubuntu in our spinning ubuntu capsule using the command “bin/bash”.

• docker exec This command runs a new command in already spinning capsules.

Stopping the Running Capsules

We need its id to stop a Running capsule and run this command.

ˆdocker stop ID_OF_CONTAINER

Conclusion

In this article, we learned some basics codes of docker to manage docker services and performed some Linux-based docker commands.

• We discussed commands for managing capsules, docker-images, and the docker engine pulling Images from the hub to the local repository.
• We don’t need to install the docker to run its capsule, and we only need docker runtime to run a deployment.
• Docker images can be created from the project files.
• Linux natively supports docker.

Docker became daemon-less since a capsule no longer needs docker daemon to run. Docker provides us with storage layers where the capsules keep their files, and even if the tablet crashes, the stored files won’t be deleted.

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