Docker 101: How to Build Docker Images Like a Pro

Docker images are the foundation of Docker containers. They’re what allow you to package up your application and its dependencies so that you can run it anywhere, on any machine.

If you want to be a Docker pro, you need to know how to build Docker images like a pro. In this blog post, I’ll show you everything you need to know to build efficient, reusable, and production-ready Docker images.

What is a Docker image?

A Docker image is a read-only template that contains everything you need to run an application: the code, the runtime, the system tools, and the libraries.

When you build a Docker image, you’re creating a blueprint for how your application should be run. This blueprint can then be used to create Docker containers, which are the actual executable units that run your application.

Docker images are made up of a series of layers, each of which represents a different piece of the application. This makes Docker images very efficient, as only the changes between layers need to be transferred when an image is updated.

Docker images are also very portable, as they can be run on any machine that has Docker installed. This makes it easy to deploy your applications to different environments.

Why should you build Docker images?

There are many reasons why you should build Docker images. Here are a few of the most important reasons:

• Portability: Docker images are portable, which means that you can run them on any machine that has Docker installed. This makes it easy to deploy your applications to different environments.
• Reproducibility: Docker images are reproducible, which means that you can always get the same results when you build them. This is important for ensuring that your applications are always running in the same way.
• Efficiency: Docker images are efficient, which means that they take up less space and use fewer resources than traditional deployment methods. This can save you money on hosting costs.
• Security: Docker images can be scanned for security vulnerabilities, which can help you to ensure that your applications are secure.
• Scalability: Docker images can be scaled easily, which means that you can easily increase or decrease the number of containers that are running your application. This can be helpful if you need to handle sudden spikes in traffic.

If you’re looking for a way to package and deploy your applications in a portable, reproducible, efficient, secure, and scalable way, then you should consider building Docker images.

Here are some additional benefits of building Docker images:

• Ease of management: Docker images make it easy to manage your applications. You can create, update, and delete images with a single command.
• Version control: Docker images are version controlled, which means that you can track changes to your images over time. This can be helpful if you need to roll back to a previous version of your image.
• Sharing: Docker images can be shared easily with others. This can be helpful if you’re working on a team or if you want to share your application with others.

If you’re not sure whether or not you should build Docker images, I recommend giving it a try. It’s a powerful tool that can help you to package and deploy your applications more efficiently and effectively.

How to Build Docker Images Like a Pro

So, how do you build Docker images like a pro? Here are the steps involved:

1. Choose a base image. The base image is the starting point for your Docker image. It should be a lightweight image that contains the essential components that your application needs to run. There are many different base images available, so you’ll need to choose one that’s appropriate for your application. For example, if you’re building a web application, you might choose a base image that contains a web server like Nginx or Apache. When choosing a base image, it’s important to consider the size of the image. The smaller the image, the smaller your final image will be. This will make your image more efficient and will save you space on your disk.
2. Install the dependencies. Once you’ve chosen a base image, you need to install the dependencies that your application needs. You can do this using the RUN command in your Dockerfile. The RUN command allows you to execute any command in your image. This means that you can use it to install packages, create directories, and configure your application. When installing dependencies, it’s important to be selective. Only install the dependencies that your application actually needs. This will make your image smaller and more efficient.
3. Copy your application code. Once you’ve installed the dependencies, you need to copy your application code into the image. You can do this using the COPY command in your Dockerfile. The COPY command allows you to copy files from your local machine into your image. This means that you can copy your application code, configuration files, and any other files that your application needs. When copying your application code, it’s important to keep the files organized. This will make it easier to manage your image and to troubleshoot any problems that you might encounter.
4. Configure your application. Once you’ve copied your application code, you need to configure your application. This might involve setting environment variables or creating configuration files. You can configure your application using the ENV and LABEL commands in your Dockerfile. The ENV command allows you to set environment variables, and the LABEL command allows you to add metadata to your image. When configuring your application, it’s important to be clear and concise. This will make it easier for other people to understand how to use your image.
5. Build the image. Once you’ve configured your application, you can build the image using the docker build command. The docker build command takes the path to your Dockerfile as its argument, and it will create an image based on the instructions in the file. When building the image, it’s important to be patient. The build process can take some time, depending on the size of your image and the speed of your machine.

The Docker Build Context

The Docker build context is the set of files and directories that are used to build a Docker image. The build context is specified when you run the docker build command.

The build context can be a local directory, a remote Git repository, or a tarball. When you specify a local directory, all of the files and directories in that directory will be included in the build context. When you specify a remote Git repository, the repository and all of its submodules will be included in the build context. When you specify a tarball, the contents of the tarball will be included in the build context.

The build context is used by the Docker daemon to build the image. The daemon will copy the files and directories in the build context into a temporary directory on the daemon’s host machine. The daemon will then use the files and directories in the temporary directory to build the image.

The Docker build context is the set of files and directories that are used to build a Docker image. The build context is specified when you run the docker build command.

The build context can be a local directory, a remote Git repository, or a tarball. When you specify a local directory, all of the files and directories in that directory will be included in the build context. When you specify a remote Git repository, the repository and all of its submodules will be included in the build context. When you specify a tarball, the contents of the tarball will be included in the build context.

The build context is used by the Docker daemon to build the image. The daemon will copy the files and directories in the build context into a temporary directory on the daemon’s host machine. The daemon will then use the files and directories in the temporary directory to build the image.

The .dockerignore file

The .dockerignore file is a text file that contains a list of files and directories that should be excluded from the Docker build context. The .dockerignore file is similar to the .gitignore file, which is used to exclude files from Git repositories.

The .dockerignore file is used by the Docker daemon to build the image. The daemon will read the .dockerignore file and exclude any files or directories that are listed in the file. This means that the files and directories that are listed in the .dockerignore file will not be copied into the temporary directory that is used to build the image.

The .dockerignore file can be used to exclude files and directories that are not needed to build your image. This can help to make your images smaller and more efficient.

Here are some examples of files and directories that you might want to exclude from your .dockerignore file:

• Build artifacts: These are files that are created during the build process, such as temporary files and compiled binaries.
• Logs: These are files that contain the output of the build process.
• Secrets: These are files that contain sensitive information, such as passwords and API keys.
• Development tools: These are tools that are used to develop your application, such as IDEs and debuggers.

Docker build command

The docker build command is used to build Docker images. The command takes the path to a Dockerfile as its argument, and it will create an image based on the instructions in the file.

The syntax for the docker build command is as follows:

docker build [OPTIONS] PATH | URL | -

The OPTIONS parameter is a list of options that can be used to control the build process. Some of the most common options include:

• -t: This option specifies the name and tag of the image that will be created.
• -f: This option specifies the path to the Dockerfile.
• -build-arg: This option specifies a build argument that will be passed to the Dockerfile.
• -progress=false: This option suppresses the progress output from the build process.

The PATH parameter specifies the path to the Dockerfile. The URL parameter specifies the URL of a Dockerfile. The - parameter tells Docker to read the Dockerfile from standard input.

For example, the following command will build an image from the Dockerfile in the current directory and tag it as myimage:latest:

docker build -t myimage:latest .

The docker build command can be used to build images from a variety of sources. You can build images from local Dockerfiles, remote Dockerfiles, and even from tarballs.

Common Commands in a Dockerfile

Here are some of the most common commands in a Dockerfile:

• FROM: This command specifies the base image that your image will be built on. The base image is a pre-built image that contains the essential components that your application needs to run.
• RUN: This command allows you to execute any command in your image. This can be used to install dependencies, create directories, and configure your application.
• COPY: This command allows you to copy files from your local machine into your image. This can be used to copy your application code, configuration files, and any other files that your application needs.
• EXPOSE: This command specifies the ports that your image will expose. This allows other containers to connect to your image and communicate with it.
• CMD: This command specifies the command that will be executed when your image is run. This can be used to start your application or to execute a shell script.
• LABEL: This command allows you to add metadata to your image. This metadata can be used to identify your image and to store other information about it.

These are just a few of the most common commands in a Dockerfile. There are many other commands that you can use to build your images. For more information, you can refer to the official Dockerfile documentation: https://docs.docker.com/engine/reference/builder/.

Additionally, to check out a few other commonly used Docker commands, check out the following post – These 10 Docker Commands Will Change Your Life

Best practices for building Docker images

There are a few best practices that you should follow when building Docker images:

• Use a base image that is as small as possible. The smaller your base image, the smaller your final image will be.
• Only include the files and dependencies that your application needs. Don’t include anything that your application doesn’t use.
• Use the RUN command to execute commands in your image. This will allow you to install dependencies, create directories, and configure your application.
• Use the COPY command to copy files into your image. This will allow you to transfer your application code and configuration files into the image.
• Use the LABEL command to add metadata to your image. This metadata can be used to identify your image and to store other information about it.

Conclusion

In this blog post, we have discussed the basics of Docker images and the docker build command. We have seen how Docker images can be used to package and deploy applications in a portable, reproducible, efficient, secure, and scalable way. We have also seen how the docker build command can be used to build Docker images from a variety of sources.

By following the tips that we have discussed in this blog post, you can build Docker images that are easy to build, manage, and deploy. You can also use the docker build command to customize the build process and create images that meet your specific needs.

I hope this blog post has been helpful. If you have any questions, please feel free to leave a comment below.

Thank you for reading!