How to use environment variables in Docker Compose and what are the best practices for configuration management?

Environment variables in Docker Compose allow you to flexibly configure applications without changing code or configuration files. The main way to pass variables is by using files with the env extension, which are read by the Compose utility by default or connected via a special env_file directive in the service description.

To work with variables, you can use substitution syntax directly in the docker-compose.yml file. For example, an expression with a dollar sign and curly braces allows you to set a default value that will be applied if the corresponding variable is not declared in the host environment. This makes the configuration more reliable and convenient for local development.

There are several important practices for securely managing secrets and settings. You should not store production passwords and access keys in the version control system along with compose files. Instead, it is recommended to add files with real secrets to git ignores and pass them to the deployment server through secure channels or built-in CI/CD system tools.

When designing architecture, separate configurations into base files and override files for different environments. This approach allows you to use a single common file to describe the service structure, while connecting environment-specific parameters using a command-line argument to specify multiple configuration files simultaneously.