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Docker: Explained to a 5 year old. 👶🏻

When I was starting out with docker, everything was really difficult for me to figure out. But don't worry. I'm here 😉

Docker is an AMAZING tool that you just can't miss. It's EVERYWHERE!
Docker everywhere

So here's everything you need to know about docker, in ONE blog. Don't worry - I'll keep it very short and concise ⚡
I'll walk you through the concepts - Containers, Images, etc. And then we'll write our own Dockerfile to containerize a very simple python application!

Table of Contents

What is docker?

Docker is a way to containerize applications (putting code in boxes that can work on their own). It magically makes a virtual computer, but guess what - they aren't really virtual computers.

Containers are boxes that have no host Operating system, so they are independent of the device they run on.

Think of it like this - there's a bee that only likes to live in it's own honeycomb, and will not be able to work if it lives somewhere else. You just trap the bee in a box that looks and feels exactly like it's honeycomb. That's containerization.

Containers are made using Images

works on my machine

Docker Images

Docker Images are like templates - a craftbook that has everything to make the craft. Or, in other words, it contains a set of instructions for creating a container.

But how do you make these images (to later make containers) ?

This is done using Dockerfiles.

All about Dockerfiles

A Dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image.
Ok, let's make a Dockerfile together.

Now, we'll start with docker HANDS ON!

Quickly download docker on your device :

Now that you have it, let's write a simple flask application and containerize it!

Here's a very simple and minimal flask app
Image description

Now, even though this might be very basic, it actually needs a lot of things to run:

  • Python 3.9
  • Flask (running pip install flask)
  • exposure to port 5000

Some programs might only run on specific Operating systems - like Windows-only or Linux-only stuff.

All these problems are solved by writing a simple dockerfile, that sets up a docker image for us.
So you need to make a file called Dockerfile (exactly, without any file extension)

Here is a walkthrough:

  • use FROM to use python base image
  • use COPY to copy the file into the container
  • use RUN to pip install flask
  • use CMD to run "python" when container starts

Its as easy as that!!!

minor correction : the file should be named Dockerfile instead

Building the image and running container

Now, build to docker image using the docker build command and then run the image by using the docker run . command.

You can also use the --tag to give a name to the image and make it easier for yourself to run later

docker build --tag flask .
docker run --name flask -p 5000:5000 flask
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Here, --name is the name of the container to be run (which i'm naming flask), -p sets the port of the docker CONTAINER to your machine, so you can see your app on localhost. Finally, the flask at the name is the name of the image to be run.

More commands

That's pretty much it!!!
use the "docker ps" command to get a list of running containers,
"docker ps -a" to get list of ALL containers
"docker images" to get list of images

"docker --help" to get list of all commands

Mess around with the commands, they are self-explanatory

Read the official documentation here.

If you learnt something in this blog, make sure to 💖 it, and follow me if you REALLY liked it!

Top comments (60)

mtwn105 profile image
Amit Wani

Wish someone could have taught me like this when I was 5 😁 Awesome🚀

dhravya profile image

thanks a lot!

mohamedtammam profile image
Mohamed Tammam

Docker wasn't there when you were 5 😂

dhravya profile image

You can map the container's port to your device's port (Which can be anything you want)
so instead of -p 5000:5000 which maps the container's 5000 to your computer's 5000, you can do something like -p 5001:5000 which will show the 5000 port in the container, on 5001

dhruv194 profile image
Dhruv Mehta

Damn bro! You are just 16 years old but you explained what Docker really is in a way like you have been learning docker since you were born XD
Very well done. I am really very impressed.

just_moh_it profile image
Mohit Yadav

Haha, really!

njmsaikat profile image
Saikat Roy

Wow Really Great Explained. when I first started faced a lot of difficulties to just imagine those basic things.

dhravya profile image

I know, right! Same with me. I used to try to watch these tutorials which would be lengthy and still ended up confused with the basics

marcomoscatelli profile image
Marco Moscatelli

I am learning this concept right now and this explanation was very helpful

dhravya profile image

thank you for the feedback!

rahulkumarmalhotra profile image
Rahul Kumar

Thank you so much for this tutorial.

mgonzalo profile image
Gonzalo Muñoz

Dude!! I got to confess: today I won a battle against prejudice.
When I saw "16yr old" on yet another dev blog, I was about to nope outta here (I've had bad experiences before)
But something made me stay. I couldn't put my finger on it at first, but it turns out that you really have a knack for explaining things (not the same as writing about something). I loved the clean and concise style and even some figures like the one with the bee.
I'm almost twice your age, but today I learned from you.
Keep up the good work, and never stop growing!

dhravya profile image

it wont run both the container and your original app. but yes, if you manually do it, there will be a collision and only throne that ran first will work (the other will error out)

dontfixyourpc profile image
Richard Rhein

Awesome explanation, good idea to explain in simple words, so that everybody can understand this.

annetawamono profile image
Anneta Wamono

Your post makes me want to start messing around with Docker. Thank you for your very approachable introduction to Docker.

paimanrasoli profile image

Nice explanation 😍

dhravya profile image

Thanks a lot!

devanica profile image

Finally someone said it, and in a way that I understand it. There are tutorials for everything but publishing APIs and other "little things" gave me a lot of headaches!

dhravya profile image

Thank you! Glad I could help

jacksonkasi profile image
Jackson Kasi

wow! nice 🤗

dhravya profile image

Thank you!

thegreytangent profile image
Jason V. Castellano • Edited

This is the most precise basic explanation about docker.

dhravya profile image

Thanks a lot! Glad you liked it

tqbit profile image

But it works on my machine

Then we'll ship your machine

Got me good. Noted.