Docker Env file

27 Apr, 2023

Docker

How to securely set environment variables from a .env file in Docker Compose

Nowadays, working with code repos is a reality for everyone. Docker is another technology that is highly prevalent in the daily lives of programmers. It has become common practice to use a docker-compose file to easily run the environment. However, issues arise when these environments require sensitive configuration information. Often, developers resort to hardcoding this information, which can lead to accidentally committing it to the repository. While it is possible to remove this information from remote repos, it is still a significant headache. Prevention is the best solution.

The solution

First we will simulate an application using environment variables. For this we will create a simple Dockerfile that will print the environment variables.

Dockerfile

FROM alpine:latest
CMD echo "My name is $NAME, I am from $COUNTRY and I am a $JOB."

Now we will create our docker-compose. The docker-compose will be the entry point for our application. We will use the.

docker-compose

version: '3.9'

services:
  demo:
    build:
      context: .
      dockerfile: Dockerfile
    environment:
      - NAME=${NAME}
      - COUNTRY=${COUNTRY}
      - JOB=${JOB}

Note: We are using the ${} syntax to reference the environment variables from the .env file.

Now we will create our .env file. This file will contain the environment variables that we want to use in our application.

.env

NAME=Nelson
COUNTRY=Portugal
JOB=Developer

Let's run our environment. Run

docker-compose up --build

If everything went well, you should see the following output:

demo_1  | My name is DSKT-NelsonBN, I am from Portugal and I am a Developer.

To finish, we will add the .env file to the .gitignore file.

echo ".env" >> .gitignore

Note: Now you can see that your .env file is no longer visible in the git status.

Note: In my demo the file is versioned, so we can see all the configuration. However, in your case, the file should not be versioned.

You can test using the command:

git status