I recently installed a Kentico website on an Azure App Service. Kentico has a scheduler service that pings an ASHX file on the same website to kickoff scheduled tasks that need to run. The request is sent from the Kentico application to itself but it leaves the server as a web request and comes back. The scheduler service was setup to request this every 60 seconds. In the Kentico event log there were 403 Forbidden errors every 60 seconds from an IP address we had already created an access rule for in Azure.
For example, the error would state the IP address of the request was 111.3.102.102 but we granted access to that IP in the Networking / Access Restrictions part of the App Service already.
Why is the request blocked?
The Kentico Event Log was showing where the request originated from but the Azure App Service was blocking its own Outbound Public IP Addresses. I had to add access rules to allow all of the Outbound IP addresses.
I found the Outbound IP addresses on the Properties page of the Azure App Service and added all of them (there were 5) to the Networking > Access Restrictions page of the Azure App Service.