Sonarqube uses a database to host configuration, tracking and other, non-BLOB data. Sonarqube supports a couple of different database back-ends. This stack-set makes use of PGSQL. The make_sonarqube_RDS.tmplt.json template deploys a small, multi-AZ database to provide for Sonarqube's database needs. Being externalized, loss of an EC2 instance does not result in the loss of database contents. Leveraging AWS's RDS also means that backups and version upgrades are handled by the CSP. Using a multi-AZ design means that, even if an AZ becomes unavailable, the Sonarqube-hosting EC2 can still contact its database (or can be re-deployed to an AZ hat still has RDS connectivity).
This template can also be used to stand up a clone of an existing RDS-deployment. To do so, add the ARN of the source-stack's most recent RDS snapshot. This can be one of the daily snapshots - or, probably better, a manual snapshot completed just before launching the parent stack.
Note: Whether the resultant RDS configuration is multi-AZ or not depends on the options selected by the template-user. Selecting the single-AZ option lowers accumulated AWS service charges but does so at the expense of design-resiliency.