Synchronising in memory data between Azure Front Door back end instances

Question

I have a web application in Azure. There are 2 instances, with Azure Front Door being used to route all traffic to the primary instance only, with the secondary one only ever used if the first is unavailable. We have some in memory data that gets updated by users. The database is subsequently updated with the changes. The data is kept in memory as a function of a genuine performance requirement. The issue we have is the data is fetched from the database only on application start up, meaning that if the primary instance becomes unavailable the secondary one could very well have information that is out of date. I was hoping that Front Door could be configured to trigger an API when any sort of switch - from primary to secondary or vice versa - occurs. However I can't find any reference to this in the documentation.

We have a series on web jobs that run, one of which is triggered every minute. However using this to keep the data fresh still doesn't guarantee that an instance will necessarily have the latest information.

Any thoughts on how to rectify this issue very much appreciated.

[EDIT]. Both web apps talk to the same database instance

Answer 1

Unfortunately Azure Front Door doesn't have any native support for firing events to something like an Event Hub but you could stream your logs to one. For example you could stream "FrontDoorAccessLog" to an Event Hub and have a script receive these events. When the "OriginName" value changes you could inform the failover app to update its state via an API.

Is there a reason why both Webapps have their own database if they have to be somewhat synchronized? Why not have both Webapps talking to the same DB?