Yesterday, I wanted to make a breaking change to my [build-configs project]({{site.url}}/archive/2023/03/04/why-i-built-a-tool-to-generate-configuration-files) - changing the default database credentials that are used by Docker Compose.
As I have several projects based on generated files by the tool, changing the values could cause issues in those projects in the future and this is something that I wanted to avoid.
## What did I do?
To avoid this issue and needing to update all of my projects at once, I added a feature flag to the `build.yaml` file so I can opt-in to this feature on a per-project basis.
If a project, like my [Drupal](https://github.com/opdavies/docker-example-drupal) and [LocalGov Drupal](https://github.com/opdavies/docker-example-drupal-localgov) Docker examples, are opted in, its files will get the new credentials. If not, it will continue to use the original ones.
[In this commit](https://github.com/opdavies/docker-example-drupal/commit/3f496168d5c32f9706970519023b431ee02c4b19), you'll see where I enabled the feature flag and committed the resulting change.
## What does this achieve?
I can continue to work on existing projects without them breaking, and migrate projects one at a time by using the feature flag instead of needing to do them all once.
Once all active projects have been migrated or completed, the feature flag can be removed and I can refactor and simplify the code - removing the feature flag and the legacy values.
