Hi Haitham,
The App servers, when nodes on a Kubernetes cluster, can connect to the same DB. See here for details: https://github.com/aws-ia/terraform-aws-mendix-private-cloud/tree/main. It's written for AWS, but you will get the point for Azure and on-prem, too. Another good source is here: https://docs.mendix.com/refguide/clustered-mendix-runtime/ including the limitations https://docs.mendix.com/refguide/clustered-mendix-runtime/
For the database, I'm looking at https://www.yugabyte.com/. We are planning to test Yugabyte in the next weeks. From an architecture point of view, it should work as it is 100% PostgreSQL. I haven't experience with an active-active MSSQL DB. For Mendix, it is important to see the database on one IP address regardless of what node is servicing.
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