Expose configuration to your applications (via environment variables). If you have multiple applications which need the same configuration items (for instance credentials for an external service), you can create an addon dedicated to expose configuration to these applications.
In addition to not copying configuration in each application, every modification of your environment variables triggers automatic deployment of the linked applications.
Create the addon
Click on "Add an add-on", then choose "Configuration provider" and select the applications
you want to link. On the dashboard, click on "edit" and input the environment variables.
The syntax is
NAME=value, like in the "expert mode" of the environment variables pannel.
Once you click "save", all the linked applications will be restarted.