Difference between revisions of "Docker/C2/Building-Docker-Images/English"

Welcome

Learning Objectives

• Building Docker images
• Pushing images to Docker Hub
• Image layers and size optimization

System Requirements

• Ubuntu Linux OS 22.04 and
• Docker version 27.0.2

• You must have basic knowledge of using Linux terminal
• For pre-requisite Linux tutorials, please visit this website

Code files

• The files used in this tutorial are provided in the Code files link.
• Please download and extract the files.
• Make a copy and then use them while practicing.

• Write a Dockerfile and required code files
• Build the Docker image
• Run the Docker image
• Push to Docker Hub
• Pull and run the image on the target machine

Building Docker Image Process Flowchart

This flowchart explains the process of building a Docker image.

Hover over Dockerfile block

Building Docker Image Process Flowchart

Building Docker Image Process Flowchart

We need a nodejs environment for running the Express web server.

Building Docker Image Process Flowchart

A new container will be created based on the image.

It will execute the commands and run the Express server on our Linux OS.

Point to Downloads folder

Let us open the Dockerfile in the text editor.

This is the base image for the application.

Open app.js

The application will listen for incoming HTTP requests on this port.

res.send("Express server is running");

});

It then sends back the message, Express server is running.

console.log(`Server started at http://localhost:${PORT}`);

});

It indicates that the server has started at the given site.

The flag hyphen t tags the image with a name.

In this case, the image will be tagged as node hyphen express with version 1.

If version is not specifically mentioned, latest will be given by default.

The dot represents the path of the current directory.

Also, we can see details about its Tag, Image ID, creation date, and size.

Tag identifies a specific version of the image.

In this case, we have given it as v1.

Our image is now successfully built.

Type the command as shown.

It helps in cleaning up resources.

You can do so by clicking on the plus symbol on the top panel of the terminal.

Enter the password when prompted.

This will retrieve the list of running containers.

Copy the container id.

Type sudo space docker space stop space and paste the container id.

Press Enter.

Pushing Images to Docker Hub

Before pushing, we need to tag the image.

It needs to be done with our Docker Hub username and the repository name.

https://hub.docker.com/

Create your account by signing up.

On the top left corner, click the list icon and choose the repositories section.

The repositories section lists repositories, each containing Docker images.

Close the previous terminal session and use a new one.

Type the command as shown.

Using this command, we will log into our Docker Hub account.

Then we can easily pull and push images to it.

Press Enter

Enter the credentials for Docker Hub when prompted.

To tag the image, enter the command as shown.

This creates a reference to the image with the specified tag.

Here, stuser1 is my username.

Substitute it with your username.

It will be assigned after pushing the image to Docker Hub.

For that, firstl et us delete the image from our local system.

Enter the command as shown.

We can see that the tagged image is no longer in the list.

For that, type the command as shown and press Enter.

Image Layers and Size Optimization

Each Dockerfile instruction that changes the filesystem, represents a layer.

To optimize image size, the number of layers are reduced.

First, we will check the size of our image.

Type the command as shown.

We don’t need to specifyany version or tag of the image.

It filters the image list and retrieves details for the specified image name only.

This size may be different for you.

Enter the password when prompted.

However, WORKDIR and CMD do not create new filesystem layers.

Thus , the Docker image will have four layers from the Dockerfile instructions.

To reduce the size, we can use a smaller base image.

Then save by pressing Ctrl+S and exit by pressing Ctrl+X.

Type the command as shown and press Enter.

Enter the commandas shown.

This size may be different for you.

Summary

In this tutorial, we have learnt about

• Building Docker images
• Pushing images to Docker Hub
• Image layers and size optimization

Assignment

• Modify the image size by using alpine variant base image.
• Compare the sizes before and after modifying the base image.

Assignment Observation

This size may be different for you.

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