May 31, 2023

What Is Docker? | What Is Docker And How It Works? | Docker Tutorial For Beginners | Simplilearn

Published May 23, 2023, 5:20 p.m. by Courtney

What is Docker?

Docker is a tool that enables you to create, deploy, and run applications by using containers. Containers allow you to package an application with all of its dependencies and ship it as one package. By using containers, you can run multiple applications on a single host without the need to worry about conflicting dependencies.

Docker is used by many organizations, including Facebook, Google, and Microsoft, to run their production workloads. In this tutorial, you will learn the basics of Docker by creating and running a simple container.

What are containers?

Containers are a way to package software in a format that can be run on any machine that has a container runtime installed. A container runtime is a piece of software that enables you to create and run containers.

Docker is the most popular container runtime. Other popular container runtimes are rkt and lxc.

What is a Dockerfile?

A Dockerfile is a text file that contains instructions for how to build a Docker image. A Docker image is a file that contains all the dependencies for an application.

In this tutorial, you will learn how to create a simple Dockerfile and build a Docker image from it.

How does Docker work?

Docker uses a client-server architecture. The Docker client is used to interact with the Docker daemon. The Docker daemon is responsible for creating, running, and managing containers.

The Docker client and daemon can be run on the same host or on different hosts. When they are run on the same host, the Docker client and daemon communicate via a Unix socket. When they are run on different hosts, the Docker client and daemon communicate over TCP.

The Docker client and daemon communicate using the Docker API. The Docker API is used by the Docker CLI and by third-party tools to interact with the Docker daemon.

How do I install Docker?

Docker is available for a variety of operating systems, including Windows, macOS, and Linux. You can install Docker on your host by following the instructions in the Docker documentation.

Once you have installed Docker, you can run the docker command to interact with the Docker daemon.


In this tutorial, you learned the basics of Docker. You learned how to create a simple Dockerfile and build a Docker image from it. You also learned how to run a container from a Docker image.

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hello this is Matthew from simply learn

and today we're gonna cover what is

docker and why it should be of value to

you as somebody who works in DevOps so

let's take a throw scenario a very

developer Etna testa before you had the

world of docker a developer would

actually build their code and then

they'd send it to the tester but then

the code wouldn't work on their system

coders are worldly a system due to the

differences in computer environments so

what could be the solution to this well

you could go ahead and create a virtual

machine to be the same of the solution

in both areas what do you think docker

is an even better solution so let's kind

of break out what the main big

differences are between docker and

virtual machines as you can see between

the left and the right hand side both

look to be very similar what you'll see

however is that on the docker side what

you'll see as a big difference is that

the guest OS for each container has been

eliminated docker is inherently more

lightweight but provides the same

functionality as a virtual machine so

let's step through some of the pros and

cons of a virtual machine versus docker

so first of all a virtual machine

occupies a lot more memory space on the

host machine

in contrast Dhaka occupies significantly

less memory space the boot up time

between both is very different docker

just boots up faster the performance of

the docker environment is actually

better and more consistent than the

virtual machine docker is also very easy

to set up and very easy to scale the

efficiencies therefore a much higher

with a docker environment versus a

virtual machine environment and you'll

find it is easier to port docker across

multiple platforms than a virtual

machine finally the space allocation

between docker and a virtual machine is

significant when you don't have to

include the guest Oh

you're eliminating a significant amount

of space and the dock environment is

just inherently smaller so after darker

as a developer you can build out your

solution and send it to a tester and as

long as we're all running in the doctor

environment everything will work just

great so let's step through what can I

cover in this presentation we're gonna

look at the DevOps tools and where

docker fits within that space we'll

examine what docker actually is and how

docker works and then finally we'll step

through the different components of the

docker environment so what is DevOps

DevOps is a collaboration between the

development team the operation team

allowing you to continuously deliver

solutions and applications and services

that both delight and improve the

efficiency of your customers if you look

at the Venn diagram that we have here on

the left hand side we have development

on the right hand side we have operation

and then there's a cross over in the

middle and that's where the DevOps team

sits if we look at the areas of

integration between both groups

developers are really interested in

planning code building and testing and

operations want to be able to

efficiently deploy operate a monitor

when you can have both groups

interacting with each other on these

seven key and elements then you can have

the efficiencies of an excellent DevOps

team so planning in codebase we use

tools like JIT and Guerra

for building we use Gradle and mavin

testing we use selenium the integration

between dev and ops is through tools

such as Jenkins

and then the deployment operation is

done with tools such as docker and share

finally nagas is used to monitor the

entire environment so let's step deeper

into what docker actually is so docker

is a tool which is used to automate the

deployment applications in a lightweight

container so the application can work

efficiently in different environments no

it's important to note that the

container is actually a software package

that consists of all the dependencies

required to run the application

so multiple containers can run on the

same hardware the containers are

maintained in isolated environments

they're highly productive and they're

quick and easy to configure so let's

take an example of what dogger is by

using a house that may be rented for

someone using Airbnb so in the house

there are three rooms and only one

cupboard and kitchen and the problem we

have is that none of the guests are

really ready to share the cupboard and

kitchen because every individual has a

different preference when it comes to

how the cupboard should be stocked and

how the kitchen should be used this is

very similar to how we run software

applications today each of the

applications could end up using

different frameworks so you may have a

framework such as rails perfect and

flask and you may want to have them

running for different applications for

different situations this is where

docker will help you run the

applications with the suitable

frameworks so let's go back to our

Airbnb example so we have three rooms

and a kitchen and cupboard how do we

resolve this issue well we put a kitchen

in covered in each room we can do the

same thing for computers docker provides

the suitable frameworks for each

different application and since every

application has a framework with a

suitable version this space can also

then be utilized for putting in Suffern

applications that are long and since

every application has its own framework

and suitable version the area that we

had previously stored for a framework

can be used for something else now we

can create a new application in this

instance a fourth application that uses

its own resources you know what

with these kinds of abilities to be able

to free up space on the computer

it's no wonder docker is the right

choice so let's take a closer look to

how docker actually works so when we

look at docker and we call something

Dokka we're actually referring to the

base engine which actually is installed

on the host machine that has all the

different components that run your

docker environment and if we look at the

image on the left-hand side of the

screen you'll see that docker

has a client-server relationship there

is a client installed on the hardware

there is a client that contains the

docker product and then there is a

server which controls how that docker

client is created the communication that

goes back and forth to be able to share

the knowledge on that docker client

relationship is done through a REST API

this is fantastic news because that

means that you can actually interface

and program that API so we look here in

the animation we see that the docker

client is constantly communicating back

to the server information about the

infrastructure and it's using this REST

API as that communication channel the

dock a server then we'll check out the

requests and the interaction necessary

for it to be the docker daemon which

runs on the server itself will then

check out the interaction and the

necessary operating system pieces needed

to be able to run the container okay so

that's just an overview of the docker

engine which is probably where you're

going to spend most of your time but

there are some other components that

form the infrastructure for docker let's

dig into those a little bit deeper as

well so what we're going to do now is

break out the four main components that

comprise of the docker environment the

four components are as follows the

docker clientís server which we've

already done a deeper dive on docker

images docker containers and the dagger

registry so if we look at the structure

that we have here on the left-hand side

you see the relationship between the

docker client and the darkest server and

then we have the rest api in between now

if we start digging into that rest api

particularly the relationship with the

daka daemon on the server we actually

have our other elements that form the

different components of the docker

ecosystem so the docker client is

accessed from your terminal window so if

you are using Windows this can be

PowerShell on Mac it's going to be your

terminal window and it allows you to run

the docker daemon and the registry

service when you have your terminal

window open so you can actually use your

terminal window to create instructions

on how to build and run your

images and containers if we look at the

images part of our registry here we

actually see that the image is really

just a template with the instructions

used for creating the containers which

you use within docker the document image

is built using a file called the docker

file and then once you've created that

docker file you store that image in the

docker hub or registry and that allows

other people to be able to access the

same structure of a docker environment

that you've created the syntax of

creating the image is fairly simple it's

something that you'll be able to get

your arms around very quickly and

essentially what you're doing is you're

creating the option of a new container

you're identifying what the image will

look like what are the commands that are

needed and the arguments for and then

those commands and once you've done that

you have a definition for what your

image will look like so if we look here

at what the container itself looks like

is that the container is a standalone

executable package which includes

applications and their dependencies it's

the instructions for what your

environment will look like so you can be

consistent in how that environment is

shared between multiple developers

testing units and other people within

your DevOps team now the thing that's

great about working with docker is that

it's so lightweight that you can

actually run multiple docker containers

in the same infrastructure and share the

same operating system this is its

strength it allows you to be able to

create those multiple environments that

you need for multiple projects so you're

working on interestingly though within

each container that contain it creates

an isolated area for the applications to

run so while you can run multiple

containers in an infrastructure each of

those containers are completely isolated

they're protected so that you can

actually control how your solutions work

there now as a team you may start off

with one or two developers on your team

but when a project starts becoming more

important and you start adding in more

people to your team you may have 15

people that are offshore you may have 10

people that are local you may have 15

consultants that are working on your


you have a need for each of those two

verbs or each person on your team to

have access to that docket image and to

get access to that image we use a docker

registry which is an open source server

site servers for hosting and

distributing the images that you have

defined you can also use docker itself

as its own default Rattray and docker

hub now something it has to be very

mindful is that

for publicly shared images you may want

to have your own private images in which

case you would do that through your own

registry so once again public

repositories can be used to host the

docket images which can be accessed by

anyone and I really encourage you to go

out to docker and see the other docket

images that have been created because

there may be tools there that you can

use to speed up your own development

environments now you will also get to a

point where you start creating

environments that are very specific to

the solutions that you are building and

when you get to that point you'll likely

want to create a private repository so

you're not sharing that knowledge with

the world in general now the way in

which you connect with the docker

registry is through simple pull and push

commands that you run through terminal

window to be able to get the latest

information so if you want to be able to

build your own container what you'll

start doing is using the pull commands

to actually pull the image from the

docker repository and the command line

that is fairly simple in terminal window

you would write docker

pull and then you put in the image name

and any tags associated with that image

and use the command pools so in your

terminal window you would actually use a

simple line of command once you've

actually connected to your docker

environment and that command will be

docker pull with the image name and any

associated tags around that image what

that will then do is pour the image from

the docker repository whether that's a

public repository or a private one now

in Reverse if you want to be able to

update the docker image with a new

information you do a push command where

you would take the script that you've

written about the docker container that

you defined and push it to the

repository and as you can imagine the

commands for that are also fairly simple


terminal window you would write darker

push the image name any associated tags

and then that would then push that image

to the docker repository again either a

public or a private repository so if we

recap the docker file creates a docker

image that's using the build commands

docket image then contains all the

information necessary for you to be able

to execute the project using the docket

image any user can run the code in order

to create a docker container and once

the docket images build is uploaded to a

registry or to a docker hub where it can

be shared across your entire team and

from the docker hub users can get access

to the docket image and build their own

new containers so the five key takeaways

here so with a virtual machine you're

able to create a virtualized environment

to run an application on an operating

system with docker it allows you to

focus on just running the application

and doing it consistently it improves

the ability for teams to be able to

share environments that are consistent

from team to team it's highly productive

and it's really quick and easy to

configure the architecture of docker is

really primarily built out of four

components of which the one that you'll

use the most is the client-server

environment where as a developer you

have a client application running on

your local machine and then you connect

with a server environment where you're

getting the latest information about

that container that you're building a

solution for and then finally what we

see with the workflow improvements with

docker is that the goal is to be able to

be more efficient to be able to be more

consistent with your development

environments and be able to push out

those environments whether it goes to a

test person to a business analyst or

anybody else on your DevOps team so they

have a consistent environment that looks

and acts exactly like your production

environment and can be eventually pushed

out to a production environment using

tools such as puppet or chef so you're

creating a consistent operations

environment really hope you've enjoyed

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