A container's environment is not set until there's an explicit entry in the service configuration to make this happen. With Compose, there are two ways you can set environment variables in your containers with your Compose file.

Tip

Don't use environment variables to pass sensitive information, such as passwords, in to your containers. Use secrets instead.

Use the environment attribute#

You can set environment variables directly in your container's environment with the environment attribute in your compose.yml.

It supports both list and mapping syntax:

services:
  webapp:
    environment:
      DEBUG: "true"

is equivalent to

services:
  webapp:
    environment:
      - DEBUG=true

See environment attribute for more examples on how to use it.

Additional information#

  • You can choose not to set a value and pass the environment variables from your shell straight through to your containers. It works in the same way as docker run -e VARIABLE ...: ```yaml web: environment:

    • DEBUG `` The value of theDEBUGvariable in the container is taken from the value for the same variable in the shell in which Compose is run. Note that in this case no warning is issued if theDEBUG` variable in the shell environment is not set.

  • You can also take advantage of interpolation. In the following example, the result is similar to the one above but Compose gives you a warning if the DEBUG variable is not set in the shell environment or in an .env file in the project directory.

yaml web: environment: - DEBUG=${DEBUG}

Use the env_file attribute#

A container's environment can also be set using .env files along with the env_file attribute.

services:
  webapp:
    env_file: "webapp.env"

Using an .env file lets you to use the same file for use by a plain docker run --env-file ... command, or to share the same .env file within multiple services without the need to duplicate a long environment YAML block.

It can also help you keep your environment variables separate from your main configuration file, providing a more organized and secure way to manage sensitive information, as you do not need to place your .env file in the root of your project's directory.

The env_file attribute also lets you use multiple .env files in your Compose application.

The paths to your .env file, specified in the env_file attribute, are relative to the location of your compose.yml file.

[!IMPORTANT]

Interpolation in .env files is a Docker Compose CLI feature.

It is not supported when running docker run --env-file ....

Additional information#

  • If multiple files are specified, they are evaluated in order and can override values set in previous files.
  • In addition, as the .env file supports interpolation, it is possible to combine those with values set by environment.
  • As of Docker Compose version 2.24.0, you can set your .env file, defined by the env_file attribute, to be optional by using the required field. When required is set to false and the .env file is missing, Compose silently ignores the entry. ```yaml env_file:
    • path: ./default.env required: true # default
    • path: ./override.env required: false ```
  • Values in your .env file can be overridden from the command line by using docker compose run -e.

Set environment variables with docker compose run --env#

Similar to docker run --env, you can set environment variables temporarily with docker compose run --env or its short form docker compose run -e:

$ docker compose run -e DEBUG=1 web python console.py

Additional information#

  • You can also pass a variable from the shell or your environment files by not giving it a value:

console $ docker compose run -e DEBUG web python console.py

The value of the DEBUG variable in the container is taken from the value for the same variable in the shell in which Compose is run or from the environment files.

Further resources#