Dockerfile Arg

Dockerfile Arg

Understanding Dockerfile ARG

Dockerfile ARG is a directive used in Dockerfile to define variables that users can pass at build-time to the builder with the docker build command. These variables can be used to modify the behavior of the Dockerfile during the build process. In this article, we will explore the usage of ARG in Dockerfile and understand its significance.

What is Dockerfile ARG?

Dockerfile ARG allows you to define variables that can be used in your Dockerfile. These variables can be passed at build-time using the --build-arg flag with the docker build command. They can be used to set default values, provide build-time parameters, or make the build process more flexible.

Using ARG in Dockerfile

To use ARG in Dockerfile, you need to define the variables using the ARG directive. For example:


These variables can then be used in the Dockerfile using the ${var_name} syntax. For example:

ENV http_proxy ${HTTP_PROXY}
ENV https_proxy ${HTTPS_PROXY}

When building the image, you can pass values to these variables using the --build-arg flag. For example:

docker build --build-arg HTTP_PROXY= --build-arg HTTPS_PROXY= .

Benefits of Using ARG in Dockerfile

Using ARG in Dockerfile brings several benefits:

  1. Dynamic build configuration: ARG allows you to customize the build process by passing different values at build-time. This makes your Dockerfile more flexible and reusable.

  2. Improved security: ARG can be used to pass sensitive information, such as passwords or API keys, securely to the build process. You can avoid hardcoding these values in the Dockerfile and pass them as build-time arguments instead.

  3. Build caching optimization: By using ARG, you can control which steps of the build process should be invalidated and re-executed when the value of a build-time argument changes. This can improve build performance by leveraging Docker's build cache.

  4. Simplified maintenance: With ARG, you can define variables for commonly used values, such as package versions or file paths, making it easier to maintain and update your Dockerfile.

Best Practices for Using ARG in Dockerfile

To make the best use of ARG in Dockerfile, consider the following best practices:

  1. Define default values: Provide default values for your ARG variables to ensure that the build process runs smoothly even if no value is explicitly passed at build-time.

  2. Document the usage: Clearly document the ARG variables and their expected values in the Dockerfile or accompanying documentation. This will make it easier for other developers to understand and use your Dockerfile.

  3. Avoid sensitive information: While ARG can be used to pass sensitive information, it is recommended to use other methods, such as Docker secrets or environment variables, for better security.

  4. Keep ARG close to its usage: Define the ARG variables close to where they are used in the Dockerfile. This improves readability and maintains a clear connection between the variable and its usage.

Related Articles

To learn more about Docker and related topics, check out the following articles:

  1. Dockerfile Copy: Simplifying Container Image Creation.
  2. Docker Build: Simplifying Container Deployment.
  3. Docker Pause Container: A Deep Dive into Container Suspension.
  4. Docker Resource Management: Maximizing Efficiency and Performance.
  5. Docker Clear Cache: Speed Up Your Development Process.

These articles cover various aspects of Docker and containerization, providing you with a comprehensive understanding of the topic.

In conclusion, Dockerfile ARG is a powerful directive that allows you to define and use build-time variables in your Dockerfile. By leveraging ARG, you can enhance the flexibility, security, and performance of your Docker image builds. Use it wisely and explore the recommended articles to expand your knowledge further.

Happy Dockerizing!

Related video


What is Dockerfile ARG?

Dockerfile ARG is a directive to define build-time variables in Dockerfile.

How do you use ARG in Dockerfile?

Use the ARG directive to define the variables and pass values using --build-arg flag.

What are the benefits of using ARG in Dockerfile?

Dynamic build configuration, improved security, build caching optimization, simplified maintenance.

What are the best practices for using ARG in Dockerfile?

Define default values, document usage, avoid sensitive info, keep ARG close to its usage.

Can ARG be used to pass sensitive information?

Yes, but it's recommended to use other secure methods for sensitive information.

What is the purpose of default values for ARG variables?

Default values ensure smooth build process even when no value is passed.

How can ARG variables be used in a Dockerfile?

Use ${var_name} syntax to use ARG variables in the Dockerfile.

Can ARG improve build performance?

Yes, by controlling invalidation of build steps and leveraging Docker's build cache.

Where should ARG variables be defined in Dockerfile?

Define ARG variables close to where they are used for better readability.

What are related articles to learn more about Docker?

Check out Dockerfile Copy, Docker Build, Docker Pause Container, Docker Resource Management, and Docker Clear Cache articles.

Ruslan Osipov
Author: Ruslan Osipov