silverstripe-framework/docs/en/02_Developer_Guides/04_Configuration/03_Environment_Variables.md

title: Environment Variables summary: Site configuration variables such as database connection details, environment type and remote login information.

Environment Variables

Environment specific variables like database connection details, API keys and other server configuration should be kept outside the application code in a separate _ss_environment.php file. This file is stored outside the web root and version control for security reasons.

For more information on the environment file, see the Environment Management documentation.

Data which isn't sensitive that can be in version control but is mostly static such as constants is best suited to be included through the Configuration API based on the standard environment types (dev / test / live).