Various databases are supported by the Cache Engine of the Denodo Virtual DataPort as can be seen in the [List of databases supported by the Cache Engine](https://community.denodo.com/docs/html/browse/7.0/vdp/administration/cache_module/cache_module#list-of-databases-supported-by-the-cache-engine). Even though Amazon RDS is not included in the list, Virtual DataPort provides a generic adapter that can be used with any other JDBC database to store cached data. You can refer to the [Generic Support for Other Databases](https://community.denodo.com/docs/html/browse/7.0/vdp/administration/cache_module/generic_support_for_other_databases/generic_support_for_other_databases#generic-support-for-other-databases) document for steps on how to configure it. However, it is strongly recommended to use one of the databases of the list above because the performance when querying the cache database will be better. The reason is that Virtual DataPort will push down more operations to the supported databases than the generic one.
Denodo Data Catalog comes with an embedded database, Apache Derby, where it stores all of its metadata. However, you can choose another database to store the metadata. You can find the list of supported databases in the [Configure the Internal Database Used by the Data Catalog](https://community.denodo.com/docs/html/browse/7.0/vdp/data_catalog/administration/servers_configuration/servers_configuration#configure-the-internal-database-used-by-the-data-catalog) document. Please note that unlike cache where Virtual DataPort provides a generic adapter to use any other databases which are not in the list, for Data Catalog you would have to choose among the ones in the list.
Hope this helps!