A Complete Beginner's Guide to Docker

A Complete Beginner's Guide to Docker

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Docker is an open-source platform that allows us to create, deploy, and manage containerized applications. In this article, we will look at

What is Docker

Docker is a container management service. Docker's entire purpose is to make it simple for developers to create apps, ship them into containers, and then deploy them wherever they want. Now let's discuss what are containers.

Containers are a solution to the challenge of moving software from one computing environment to another and having it operate consistently. This might be from a developer's laptop to a test environment, or from a real data center computer to a virtual machine in a private or public cloud.

A container is a whole runtime environment packaged into one package: a program, together with all of its dependencies, libraries, and other components, and configuration files needed to run it. Now that you have some knowledge about Docker and Containers, let understand why should we use Docker.

Benefits of Using Docker

Before installing docker and dockerizing an application let's first understand what are the advantages of Docker. Running applications in containers brings a number of benefits such as

Performance

Docker containers are usually fast and less resource-intensive than virtual machines because containers do not contain an operating system whereas virtual machines do.

Scalability

You can quickly create new containers if demand for your applications requires them. When using multiple containers you can take advantage of a range of container management options.

Rapid Deployment

Docker manages to reduce deployment to seconds. This is because it generates a container for each process and does not boot an operating system.

CI Efficiency

Docker allows you to create a container image and utilize it throughout the whole deployment process. The ability to isolate non-dependent stages and perform them in parallel is a major advantage.

Now lets learn the facts about Docker that you might don't know :)

Docker Facts

  • Docker adoption is up 30% in the last year.
  • PHP, Ruby, Java, and Node are the main programming frameworks/languages used in containers.
  • 2/3 of organizations that try Docker end up utilizing it. The majority of firms who will adapt did so within 30 days of first production use, and virtually all of the remaining adopters converted within 60 days.
  • Docker offers a large library of pre-built images. At the time of writing, there are over 400,000 public Docker images available on the web.

Installation of docker

Mac

If you are using Mac with Apple silicon you must install Rosetta 2, to do that simply run the below command in your terminal.

softwareupdate --install-rosetta

Visit this link and select your mac chip, Click on the blue button with your mac chip label on it. Once you did a DMG file will be downloaded, double click on it, and you need to drag the docker logo into Applications folder
Screenshot 2021-10-07 at 07.50.28.png

Once it is copied, you will be able to access docker from the Applications folder.

Screenshot 2021-10-07 at 07.52.44.png

Linux

To install Docker in Linux you can simply run the below command in your terminal, this would install everything related to docker in your Linux machine.

wget -qO- https://get.docker.com | sh

Dockerizing a node.js app

Dockerizing is the process of packing, deploying, and running applications using Docker containers. In this article, we are going to dockerize a node.js application, but before starting it, If you are using VS Code, It is better to install Docker extension.

Screenshot 2021-10-08 at 08.01.53.png

The Docker extension makes it easy to build, manage, and deploy containerized applications from Visual Studio Code. It also provides one-click debugging of Node.js, Python, and .NET Core inside a container.

Environment Setup

In this article, I am going to create a simple node.js application that send a get request, but if you want, you can also continue dockerizing your current application throughout this article.

To create a node.js app from scratch, you just need to run

npm init

Once you complete it, a package.json file will be generated. Now you can create a new file named app.js and this is going to be the file where we will be dockerizing it. To send/get the http request we need to set up express too, so also need to install express.js. To do that simply run

npm i express

and once it is done, you can create a simple GET request. Here is the code for it :)

const express = require("express");

const app = express();

app.get("/", (req, res) => {
  res.send({
    message: "Hey, server is running :D",
  });
});

const port = process.env.PORT || 3000;
app.listen(port, () => {
  console.log(`Server is running on port ${port}`);
});

You can run this app by running node app.js and your server will start on port 3000. You can open your browser and go to localhost:3000 in which your app is running and you will see similar output ( below image ).

Screenshot 2021-10-08 at 17.51.30.png

Now that we have our basic node.js app setup, let's start learning about Dockerfile.

Dockerfile

A Dockerfile is a text file that contains all of the commands that a user may use to construct an image from the command line.

Dockerfile.png

Now, go ahead and create a Dockerfile inside of your project directory. The first thing we need to do is define from what image we want to build from. Copy the below code and paste it into your dockerfile. Don't worry I am going to explain each line :)

FROM node:14

WORKDIR /app

COPY package*.json ./

RUN npm install

COPY . .

ENV PORT=8080

EXPOSE 8080

CMD [ "node", "start" ]

In the above code

  • FROM initializes a new build stage and sets the Base Image for subsequent instructions
  • WORKDIR is used to set the working directory for all the subsequent instructions
  • COPY let you copy files from a specific location into a Docker image
  • RUN allows you to install your application and packages required for it
  • EXPOSE is a way to keep track of which ports are in use, but it does not map or open any ports.
  • CMD ​ specifies the instruction that is to be executed when a Docker container starts

We now have a full set of instructions to build a docker image, Let's build it :)

Docker Image

To build a docker image, we have to use below build command

docker build [OPTIONS] PATH | URL | -

which in our case will be

docker build -t <your username>/nodedemo .

You should change to your docker hub username

After the completion of this process, a docker image will be created. To see all your docker images, run the following command in your terminal

docker images

Docker Containers

Now that we have your docker images, we can use them as a base image to create other images or we can use it to run containers.

Usually, we use this image to push it to a container registry that might be docker hub or any cloud provider. But in this article are going to push our image to docker hub. To do that simply run

docker push <your username>/nodedemo

If you got an access denied error, then you need to login into your docker hub account, to do that run

docker login

and enter your email and password in your terminal. Once you push your image to the docker hub you can access them in your docker hub profile.

Conclusion

That is it for this article. I hope you found this article useful, if you need any help please let me know in the comment section.

You can find the source code on my Github repository here .

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👋 Thanks for reading, See you next time

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