How to Use Environment Variables in Docker

Environment variables are a crucial part of configuring Docker containers. They allow you to pass configuration parameters at runtime, making your applications more flexible and secure. In this tutorial, we will cover how to set and use environment variables in Docker containers.

1. Understanding Environment Variables

Environment variables are key-value pairs that can influence the behavior of processes in a container. They are often used to store sensitive information such as API keys, database connections, and configuration settings.

2. Setting Environment Variables in Docker

There are several ways to set environment variables when running Docker containers:

2.1. Using the -e Flag

You can pass environment variables directly using the -e flag when you run a container:

docker run -e MY_ENV_VAR=value my_image

Replace MY_ENV_VAR with your desired variable name and value with the value you want to assign.

2.2. Using an Environment File

Another method is to use an environment file. Create a file (e.g., env.list) with your variables:

MY_ENV_VAR=value
ANOTHER_VAR=another_value

Then run the container using the <code–env-file option:

docker run --env-file env.list my_image

3. Accessing Environment Variables in Your Application

Once set, you can access these environment variables in your application. For example, in a Node.js application, you can access an environment variable like this:

const myVar = process.env.MY_ENV_VAR;

In a Python application, you can use:

import os
my_var = os.getenv('MY_ENV_VAR')

4. Updating Environment Variables

If you need to update an environment variable, you usually need to recreate the container since environment variables are defined at the start. Stop and remove the old container, then create a new one with the updated value:

docker stop my_container

docker rm my_container

docker run -e MY_ENV_VAR=new_value my_image

5. Best Practices for Using Environment Variables

• Use environment variables for sensitive information to avoid hardcoding secrets in your code.
• Utilize a `.env` file to keep configurations organized. Note that you can use something like dotenv in your applications to load these variables automatically.
• Limit the number of environment variables set to only what’s necessary for your application.

6. Conclusion

Environment variables in Docker are a powerful tool for configuring applications dynamically and securely. By following the practices outlined in this tutorial, you can efficiently manage your application settings and keep sensitive information protected.

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Dorian Kane

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