Function App not working when VNet integration is enabled

Question

I have a Function App that works fine with Vnet integration. This Function App is in a resource group used for testing.
I published the same Azure Function but to a different Function App in a different resource group.
But this one doesn't work when VNet integration is enabled.

Answer 1

If your Function App in a different resource group is not working with VNet integration enabled, there could be several reasons for this issue:

1. Network Security Groups (NSGs): Check if the NSGs associated with your VNet or subnet are blocking access. Ensure that the necessary inbound and outbound rules are configured to allow traffic to and from your Function App.
2. Subnet Configuration: Verify that the subnet you are trying to integrate with is properly configured for VNet integration. The subnet should not have any conflicting configurations that might prevent the Function App from accessing it.
3. Routing Issues: Ensure that your routes are correctly configured in the subnet and that they include the necessary address ranges for your on-premises gateway if applicable.
4. Firewall Settings: If you have on-premises firewalls, make sure they are not blocking traffic from the Function App's IP range.
5. Private IP Assignment: Check if the Private IP has been assigned to all instances of the Function App. You can use the Network troubleshooter in the Azure portal to diagnose connection issues.
6. VNet Integration Settings: Ensure that the VNet integration settings are correctly applied in the Azure portal for the Function App. You can review the settings under the Networking section of your Function App.

If you continue to experience issues, consider using the Azure support resources for further assistance.

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References:

• Azure Functions networking options
• Enable virtual network integration

Answer 2

Hi @Aldo Marukot ,

Thanks for reaching out to Microsoft Q&A.

Check below steps to diagnose and resolve the problem:

Run the Network Troubleshooter which can help identify issues with your VNet configuration and connectivity to dependent resources. You can launch it from the Diagnose and Solve blade in the Azure portal. Check if it highlights any configuration or connection issues. Refer MSDOC.

1. Ensure that the VNet and subnet configurations are correct. The subnet being used for VNet integration should not already be utilized for other purposes like private endpoints. Make sure the subnet is valid for integration, without overlapping assignments. Refer MSDOC.
2. Verify that there are no firewalls or NSGs blocking access to your Function App. You may need to adjust the NSG rules to allow outbound traffic for the integration subnet. More on NSGs.
3. Sometimes, if the Function App is not reachable, it might relate to DNS settings or a misconfiguration in your VNet integration. If your app is targeting an external IP address, ensure that it's reachable from the VNet. If using custom DNS servers, check their accessibility.
4. Check the logs and metrics for the Function App to identify any specific error messages that could indicate why the app isn't functioning as expected. Always look at logs from the Azure portal, Kudu, or Application Insights, if enabled. Check Logs Here.

References:

• Network troubleshooter
• Enable virtual network integration
• Network Security Groups Overview
• Monitoring Azure Functions

Let me know if you need any further assistance!

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