Azure Front Door, Huge number of SQL Sessions .netcore (resolved)


Over 60,000 new sessions were being stored in our AZURE SQL database being used for sessions, on several occasions the DB reported errors "The request limit for the database is 120 and has been reached"

At first we thought it was a Denial of Service (DOS), but when we dug into the problem further we encountered why this was happening. If you have this and you have these items, it could be the same problem we had.

- Azure Front Door
- Azure App Service
- Azure App Service uses  AddDistributedSqlServerCache and Add Session to store sessions in a SQL database.

The solution.

For Azure front door, we had the backend pool polling for health looking for a file /logo.png, but during an update we moved this logo out of the folder.

This made the Azure front door go into a spin, the missing file generates a 404 from the system, which creates a call to the Azure Front Door and an infinite loop occurs, constantly firing up a new session to check for that missing file.


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