Introduction

This post covers everything you need to know to start using Docker.

I will begin by presenting Docker and the issues it solves, then I’ll clarify the most used terms related to Docker, and finally, we will dockerize an application and run our first container.

What Problem Does Docker Solve?

Settings up an environment can be complex for some people, especially for a less technical person.

Docker will install all the dependencies your application need; You don’t have to worry about setting up your MySQL, installing Java, node or any other tool.

If you don’t want to share the filesystem, database, network interface, port or OS … between applications docker got you covered thanks to its isolation technique.
Security - Isolation concerns security too, deploying a vulnerable application or a malicious code can damage the other applications, and that's why it’s better to keep apps isolated.
Portability - As long as the Docker versions are compatible your shipped software will work anywhere

Key terms

Docker

Docker is an open-source project that:

Will help you deploy your applications.
Packages your applications into an image that can be used anywhere.
Uses containers to run applications in isolated environments

Images

Images contain:
- Application code
- Dependencies
- Configuration
- Runtime environment

Important: Images are read-only you can’t change the content of an image; if you need to change the content of an image you have to create a new image with the changes.

Containers

A container:
- Is a runnable instance of an image.
- Completely Isolated process (runs undependably from any process on your computer).
- Help to improve the deployment of an application.

Note: We can create multiple containers from the same image.

Install Docker

Install Docker on Windows

Install WSL

WSL stands for Windows Subsystem for Linux.

It’s a feature in Windows 10 version 2004+ and windows 11; it allows Linux programs to run on Windows

To install WSL simply run this command on PowerShell

wsl --install

Alternatively, if you want to install it manually follow this guide

Manual installation steps for older versions of WSL | Microsoft Learn

Install Docker Desktop

The next step is to install the Docker Desktop

You can follow this link to download the Docker Desktop

Install Docker Desktop on Windows | Docker Documentation

The installation is really simple we won’t go into in this tutorial

Install Docker on Ubuntu

Before installing docker on your Linux system you must install some dependencies that Docker needs

sudo apt-get install ca-certificates curl gnupg lsb-release

Add the Docker GPG key

sudo mkdir -p /etc/apt/keyrings

curl -fsSL <https://download.docker.com/linux/ubuntu/gpg> | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg

Set up the repository

echo \\ "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.gpg] <https://download.docker.com/linux/ubuntu> \\ $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

And lastly, install Docker

sudo apt-get update

sudo apt-get install docker-ce docker-ce-cli containerd.io docker-compose-plugin

Install Docker on other platforms

Docker supports a variety of platforms (Linux platforms, macOS and Windows). For more details check the official documentation Install Docker Engine | Docker Documentation

Check the installation

After installing docker you can run your first container using this command

docker run hello-world

Output

Hello from Docker!

This message shows that your installation appears to be working correctly.

…

If you see this message, then congratulation you have successfully installed Docker.

DockerHub

What is DockerHub?

Docker Hub is a service provided by Docker to download and share docker images.

You can access DockerHub from this link Docker Hub Container Image Library | App Containerization

Download an image from DockerHub

Let’s say you need a Linux OS to deploy your application

1- Go to hub.docker.com and search for the OS you need to install I’ll take Ubuntu as an example

02 - hub ubuntu search.png

2- You will get a variety of images, select the image you need to install in my case the official Ubuntu image

03 - hub ubuntu.png

3- Run the docker pull ubuntu command on your terminal, CMD or PowerShell.

Output

…

Status: Downloaded newer image for ubuntu: latest docker.io/library/ubuntu:latest

Congratulation now you have downloaded your first image, you may have noticed that the image size is way smaller than the official ubuntu Iso image and that’s another advantage of docker.

Note: By default, docker pull ubuntu will pull the latest version, but you can specify the docker version following the image name example docker pull ubuntu:20.04

Note: Alternatively, if you don’t want to go to hub.docker.com and search for the image using your browser you can search for images using your command line simply type

docker search ubuntu

This command will list all the available images, their descriptions and more …

DockerFile

What is a DockerFile?

A DockerFile is a file that contains a set of instructions for docker to create your own image, for example, it may contain the OS your application will run on, the source code of your application etc…

A DockerFile does not have an extension and it contains a set of instructions

How to create a DockerFile?

We learned previously that a DockerFile is a set of instructions below are the most common instructions used on DockerFiles

FROM is used to define the parent image that the new image will be built.

COPY & ADD is used to copy files to the filesystem of the image.

WORKDIR is used to specify the working directory.

RUN is used to run commands to run inside the container.

CMD is used to specify a command that executes by default when running a Docker container.

For more DockerFile instructions visit Dockerfile reference | Docker Documentation

Example: Dockerizing a Node.js web app

Note: Optional you can install a Docker extension in your editor.

Step 1 - Define the parent container

FROM node:16

Step 2 - Define the working directory which will contain our node application

WORKDIR /usr/src/app

Note: The following instructions will be executed inside /usr/src/app

Step 3 - Copy the node application to our image

COPY . .

Note: The first dot represents the current file on our host machine, and the second dot is the current working directory.

Step 4 - Informing Docker of the port our application is listening to

EXPOSE 4444

Step 5 - Installing the application dependencies

RUN npm install

Step 6 - Lastly define the command to run the application

CMD [ "node", "server.js" ]

That’s all! The DockerFile should look like that

FROM node:16

WORKDIR /usr/src/app

COPY . .

EXPOSE 4444

RUN npm install

CMD [ "node", "server.js" ]

DockerIgnore file

The .dockerIgnore file is similar to the .gitignore you simply include the path to the files or folders you want Docker to ignore while dockerizing your application.

In the previous example, we can create a .dockerignore file to ignore the node_modules folder

Simply create a .dockerignore file and it should contain one line

node_modules

Build the Image

Now that we had set up the DockerFile and the .dockerIgnore file we can build our image

to do so simply run the following command:

docker build -t [ Type your image tag here ]

Example

docker build -t myFirstImage

Start & Stop the Container

To start the image created you can use the Docker Desktop application just go to images ⇒ select the image and click run

or we can use the command line

This command displays all the available images

docker images

and to start the container

docker run -p 8080:4444 --name [Give the container a name] [Image name]

Example:

docker run -p 8080:4444 --name myContainer myFirstImage

Note: -p 8080:4444is used to map the 8080 port to the exposed port 4444.

We will be able to access the exposed port using the 8080 port on the local host.

To see the running container run

docker ps

This command displays the running containers along with their ID, created date, and Ports

To stop the container run

docker stop [Container id or Container name]

Example:

docker stop myContainer

Conclusion

In this article you learned pretty much everything you need to get started with Docker from basic concepts, downloading and installing Docker to creating and managing your Docker images and container.

Docker cheat sheet

Category: Docker

Docker in nutshell

Links