DRY (don't repeat yourself)
What is DRY config?
Config variable names are declared once, and then flexible variable values are injected as needed across build, deploy, and run-time phases in the form of defaults, inheritances and overrides.
Why DRY config?
Avoid errors by allowing single changes to propagate where they are needed.
No more copy-and-paste errors.
Benefits
DRY solves forgetting to update critical secrets or parameters.
Synchronize related changes.
Examples
Sync both the client and server port numbers.
Rotate secrets by making a change in one place.