Introduction to Docker - Part 4

Introduction to Docker - Part 4

Written by Bobby Iliev on Apr 23rd, 2020 ・ Views ・ Report Post

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Introduction

Welcome to part 4 of my Introduction to Docker blog post series! 

In part 1 I quickly went through installing Docker and what containers are and in part 2 we actually played with Docker containers a little bit by running a couple of Docker containers, in part 3 we went got introduced to the Docker images and some basic operations. 

In this post, I'll give a quick introduction to the Dockerfile and how to use it!

I'll be using DigitalOcean for all of the demos, so I would strongly encourage you to create a DigitalOcean account follow along. You would learn more by doing!

To make things even better you can use my referral link to get a free $100 credit that you could use to deploy your virtual machines and test the guide yourself on a few DigitalOcean servers:

Digital Ocean $100 Free Credit

Once you have your account here's how to deploy your first droplet/server:

https://www.digitalocean.com/docs/droplets/how-to/create/

I'll be using Ubuntu 18.04 so I would recommend that you stick to the same so you could follow along.

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What is a Dockerfile?

A Dockerfile is basically a text file that contains all of the required commands to build a certain Docker image. 

The Dockerfile reference page: 

https://docs.docker.com/engine/reference/builder/

It lists the various commands and format details for Dockerfiles.

Dockerfile example

Here's a really basic example of how to create a Dockerfile and add our source code to an image.

First, I have a simple Hello world index.html file in my current directory that I would add to the container with the following content:

<h1>Hello World - Bobby Iliev</h1>

And I also have a Dockerfile with the following content:

FROM webdevops/php-apache-dev
MAINTAINER Bobby I.
COPY . /var/www/html
WORKDIR /var/www/html
EXPOSE 8080

Here is a screenshot of my current directory and the content of the files:

Here is a quick rundown of the Dockerfile:

- FROM - The image that we would use as a ground

- MAINTAINER - The person who would be maintaining the image

- COPY - Copy some files in the image

- WORKDIR - The directory where you want to run your commands on start

- EXPOSE - Specify a port that you would like to access the container on

Docker build

Now in order to build a new image from our Dockerfile, we need to use the docker build command. The syntax of the docker build command is the following:

docker build [OPTIONS] PATH | URL | -

The exact command that we need to run is this one:

docker build -f Dockerfile -t your_user_name/php-apache-dev .

After the built is complete you can list your images with the docker images command and also run it:

docker run -d -p 8080:80 your_user_name/php-apache-dev

And again just like we did in the last tutorial we can go ahead and publish our image:

docker login

docker push your-docker-user/name-of-image-here

Then you will be able to see your new image in your Docker Hub account (https://hub.docker.com) you can pull from the hub directly:

docker pull your-docker-user/name-of-image-here

For more information on the docker build make sure to check out the official documentation here:

https://docs.docker.com/engine/reference/commandline/build/

Knowledge Check

Once you've read this post, make sure to test your knowledge with this Dockerfile quiz:

https://quizapi.io/predefined-quizzes/basic-dockerfile-quiz

Conclusion

This is a really basic example, you could go above and beyond with your Dockerfiles!

That is pretty much it for this post! Now you know how to write a Dockerfile, how to build a new image from a Dockerfile using the docker build command!

We are ready to move to Part 5 of the Introduction to Docker blog post series:

https://devdojo.com/tutorials/introduction-to-docker-part-5

Let me know if you have any questions!

Bobby

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