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Avinash Bendigeri Avinash is a developer-turned Technical writer skilled in core content creation. He has an excellent track record of blogging in areas like Docker, Kubernetes, IoT and AI.

Ways to Pass Environment Variables to Docker Containers: -e Flag, .env File, and Docker Compose | Docker

2 min read

Environment variables are the essential tools of any programmer’s toolkit. They hold settings, configurations, and secrets that shape how our applications run. In the world of Docker containers, passing these variables effectively is crucial for smooth sailing on the high seas of deployment.

But fear not, mateys! This blog post is your nautical map, guiding you through the different ways to pass environment variables to your Docker containers. Buckle up and prepare to dive deep!

Why Pass Environment Variables?

Think of environment variables as hidden crewmates on your Docker voyage. They silently store vital information like database credentials, API keys, or application configs, ensuring everything runs smoothly without cluttering your code or Dockerfiles.

Here’s why passing environment variables is ahoy-some:

  • Decoupling: Keep sensitive information out of your code or Dockerfiles, enhancing security and flexibility.
  • Configuration Management: Easily manage different deployment environments by changing variables instead of rebuilding containers.
  • Scalability: Maintain consistency across multiple containers and deployments with centralized variable management.

The Three Musketeers of Passing Environment Variables:

Now, let’s explore the three main ways to pass these environment variables to your Docker containers:

1. The -e Flag:

This trusty first mate, the -e flag, allows you to directly set individual variables when running the docker run command. It’s like shouting orders to your container before setting sail:

docker run -d -t -i -e NAMESPACE='staging' busybox sh

If you want to use multiple environments from the command line then before every environment variable use the -e flag.


docker run -d -t -i -e NAMESPACE='staging' -e PASSWORD='foo' busybox sh

2. The .env File:

For larger crews of variables, the .env file acts as a trusty logbook. Each line defines a variable and its value, making it easy to manage and share configurations:


Then, you use the --env-file flag to tell Docker to consult this logbook before launching your container:

docker run --env-file .env my_image

3. Docker Compose:

In a grand fleet of containers, Docker Compose captains the ship. Its YAML files allow you to define environment variables for all services within your application, keeping your configuration shipshape:

version: "3.9"

      NAMESPACE: staging
      PASSWORD: foo

Choosing the Right Approach:

The best way to pass environment variables depends on your specific needs. For a quick one-off deployment, the -e flag might suffice. For larger applications, the .env file offers better organization and security. And for complex multi-container setups, Docker Compose reigns supreme.

Remember, mateys:

  • Security: When dealing with sensitive information like passwords or API keys, consider storing them securely outside your Docker environment, like in a vault or secrets management tool.
  • Testing: Always test your environment variable configurations in different environments to ensure everything runs smoothly.

With these tips in your seabag, you’ll be passing environment variables to your Docker containers like a seasoned skipper. So set sail, explore the vast ocean of possibilities, and remember, a smooth deployment is a happy deployment!

Bonus Tip:

Want to get fancy with your environment variables? Check out Docker secrets or Kubernetes ConfigMaps for even more advanced management options.

Ahoy there, fellow Docker enthusiasts! Did you find this blog post helpful? Share your favorite ways to pass environment variables in the comments below, and let’s keep the seas of deployment calm and productive!

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Avinash Bendigeri Avinash is a developer-turned Technical writer skilled in core content creation. He has an excellent track record of blogging in areas like Docker, Kubernetes, IoT and AI.

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