Including the Spring-Cloud config server would have been interesting , because it has all the mentioned features, but is running on top of git. If you are on AWS, you can use one if the free CodeCommit repos.
The cool thing is obviously the spring integration, which pulls the secrets on app startup and overwrites or augments the values in the application.(properties|yml)
It can also run kind of serverless by embedding it in your app.
The project has been used in production since the summer of 2016. It is being used by a number of teams, and has been contributed to by more than 20 developers (there is a CONTRIBUTORS file).
The backup will take the data stored in DynamoDB (or a file) and serialize to an encrypted file. It will not backup the KMS key, or IAM policies. Hence, it is useful to take snapshots of your state, but not a full disaster recovery.
You can take a backup by a click of a button in the GUI, or using the cli: `strongbox group backup --group team.project --dst-path my-file.backup`