How to use secrets in Docker Compose

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Secrets
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A secret is any piece of data, such as a password, certificate, or API key, that shouldn’t be transmitted over a network or stored unencrypted in a Dockerfile or in your application’s source code.

Docker Compose provides a way for you to use secrets without having to use environment variables to store information. If you’re injecting passwords and API keys as environment variables, you risk unintentional information exposure. Environment variables are often available to all processes, and it can be difficult to track access. They can also be printed in logs when debugging errors without your knowledge. Using secrets mitigates these risks.

Use secrets

Getting a secret into a container is a two-step process. First, define the secret using the top-level secrets element in your Compose file. Next, update your service definitions to reference the secrets they require with the secrets attribute. Compose grants access to secrets on a per-service basis.

Unlike the other methods, this permits granular access control within a service container via standard filesystem permissions.

Examples

Simple

In the following example, the frontend service is given access to the my_secret secret. In the container, /run/secrets/my_secret is set to the contents of the file ./my_secret.txt.

services:
  myapp:
    image: myapp:latest
    secrets:
      - my_secret
secrets:
  my_secret:
    file: ./my_secret.txt

Advanced

services:
   db:
     image: mysql:latest
     volumes:
       - db_data:/var/lib/mysql
     environment:
       MYSQL_ROOT_PASSWORD_FILE: /run/secrets/db_root_password
       MYSQL_DATABASE: wordpress
       MYSQL_USER: wordpress
       MYSQL_PASSWORD_FILE: /run/secrets/db_password
     secrets:
       - db_root_password
       - db_password

   wordpress:
     depends_on:
       - db
     image: wordpress:latest
     ports:
       - "8000:80"
     environment:
       WORDPRESS_DB_HOST: db:3306
       WORDPRESS_DB_USER: wordpress
       WORDPRESS_DB_PASSWORD_FILE: /run/secrets/db_password
     secrets:
       - db_password


secrets:
   db_password:
     file: db_password.txt
   db_root_password:
     file: db_root_password.txt

volumes:
    db_data:

In the advanced example above:

  • The secrets attribute under each service defines the secrets you want to inject into the specific container.
  • The top-level secrets section defines the variables db_password and db_root_password and provides the file that populates their values.
  • The deployment of each container means Docker creates a temporary filesystem mount under /run/secrets/<secret_name> with their specific values.

Note

The _FILE environment variables demonstrated here are a convention used by some images, including Docker Official Images like mysql and postgres.

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