"A cloud database is a database that typically runs on a cloud computing platform. There are two common deployment models: users can run databases on the cloud independently, using a virtual machine image, or they can purchase access to a database service, maintained by a cloud database provider. Of the databases available on the cloud, some are SQL-based and some use a NoSQL data model." source https://en.wikipedia.org/wiki/Cloud_database
When it's being run independently in a Virtual Machine Image, there is not much to add to the typical considerations to manage a database instance. It becomes interesting when the database is provided as a service.
With GeneXus you can build solutions (cloud-based or not) that run with these cloud databases provided by PaaS providers like Amazon, IBM, Google, Microsoft or others.
The following is a list of relational cloud databases that are supported by GeneXus and the corresponding Datastore property value you have to set.
Disclaimer: This is not a complete list of the supported relational cloud databases, it just shows some of the cloud databases that are available and have been tested in some way (some fully, some partially) by the GeneXus team, or are being used (or have been for some time) by some GeneXus Community members.