Introduce dotenv to Docker + Rails to manage environment variables

What you want to achieve

How to manage API keys and passwords that should not be published in Rails development using Docker in a separate file.

Rough order

  1. Add gem
  2. Describe the environment variables used in the project in the .env file.
  3. Include .env file in .gitignore
  4. Pass environment variables according to erb template

Version used


Added gem'dotenv-rails'


gem 'dotenv-rails'

Do bundle install in the container


docker-compose run container name bundle install

Edit docker-compose.yml

By writing env_file in yml, you can set to read the file that manages environment variables.


 		- .env(Describe the file name for which you want to manage environment variables)

Build a container

I edited docker-compose.yml, so I will build it again.

docker-compose build

Write the environment variables you want to set in the .env file


 MAP_API_KEY="Issued API key"

Add .env file to gitignore



Pass as an environment variable in view's erb template


Omitted above
 <script src="<%=ENV['MAP_API_KEY']%>&callback=initMap" async defer></script>

The important thing here is to write <% = ENV ['']%> according to the erb template. Without doing this, I wrote ENV ['MAP_API_KEY'] and handed it over, and I couldn't display it in view well, and it was stuck for about 2 days.

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