I just had an issue with a deployed ASP.NET app on Azure: I changed the connection string in the deployed web.config using the new App Service Editor in the Azure Portal, but the changes had no effect in my application!
This answer from StackOverflow gave me the hint I needed: My connection string was being overridden by an Application Setting in the Azure App Service. I didn’t even know that it was configured.
To see if you have a connection string defined in your Azure App service log into the Azure Portal, open your App Service and go to Settings -> Application Settings -> Connection strings.
Delete the connection string in the Azure application settings. Now you can change the connection string in the web.config using the App Service Editor, for example.
Use the Azure application settings to manage your connection strings. The values defined here will always override the connection strings from your web.config.