One of our clients has their entire infrastructure set up in Azure, with all resources securely placed behind a virtual network. Their Function App and database reside within the same network, allowing seamless communication between them.
We encountered a new requirement where our Function App needed to access a database in a different virtual network. Since both networks were isolated, direct access was not possible.
The simplest way to enable communication between different virtual networks in Azure is through VNet peering. We implemented VNet peering between the two networks and conducted a test:
• A VM from one network successfully connected to the database in the other network without any issues.
• However, when we attempted the same connection from the Function App, it failed.
The Challenge: Function App Unable to Access the Peered Network
Despite successfully establishing VNet peering, our Function App still couldn’t connect to the database in the other network. We spent considerable time researching online but couldn’t find a clear solution.
The Solution: Enabling WEBSITE_VNET_ROUTE_ALL
After extensive troubleshooting, we used the ‘Diagnose and solve problems‘ tool in Azure and navigated to Configuration and Management. Here, we discovered a configuration warning that pointed us toward the missing setting.
To resolve the issue, we added the following application setting in the Function App:
{
“name”:”WEBSITE_VNET_ROUTE_ALL”,
“value”:”1″,
“slotSetting”:false
}
Conclusion
By enabling WEBSITE_VNET_ROUTE_ALL, we successfully allowed our Function App to access the database in the peered network, resolving the issue. This experience reinforced the importance of checking Azure diagnostics and configuration settings before diving into complex troubleshooting.
If you’re facing a similar issue, be sure to verify this setting—it might save you hours of debugging! 🚀