Hello Adrian,

in our solution we use WebSocket for communication between the components (https://sdk.innovaphone.com/13r3/doc/appdevelopmentguide.htm).

My suggestion therefore is to implement a middle-ware on the external SQL server that connects on one side via WebSocket to the App Service and implements a custom JSON API, and on other side connects to the SQL server.

The middle-ware would translate JSON messages to SQL queries and vice versa. For example:

{api: "MyExternalSQL", mt: "GetUserId", name: "bob" } -> SELECT id FROM users where name='bob'; -> {api: "MyExternalSQL", mt: "GetUserIdResult", id: 123 }

This could be done on the external SQL server or other host using NodeJS.

On the innovaphone App Service side the JSON API would be handled using JsonApi Library that can accept incoming WebSocket connections.

Best Regards

Andreas Fink