Azure Functions Connectivity Issue: An IT Pro Analysis

Posted on July 28, 2025  •  2 minutes  • 347 words  

Introdcution

An application stakeholder reported an issue with an Azure Function, indicating an error message stating “The host is unreachable.” Upon inquiry, the stakeholder suggested that the Function App pattern design was flawed and that no functions were operational. Yes, this prompted a detailed investigation into the deployment and configuration and pushed me to write this blog. A professional analysis of an Azure Functions connectivity issue caused by improper network configuration and its resolution using VNET integration.

The initial step involved assessing the deployment process of the Function App. The stakeholder confirmed that the functions were not running and could not connect to the host, attributing the issue to an incorrect pattern. To clarify, the distinction between the components was reviewed:

• Function App: The hosting environment for the functions.
• Functions: Individual code units executed within the Function App.

Further analysis is required to examine the storage account configuration. The stakeholder indicated that the configuration was defined in a Terraform template, which had not been modified. It was determined that the storage account was deployed without public internet access. The stakeholder emphasised the security measures, noting that the network was intentionally isolated.

Organisation Rule

1. No storage account should be public. There is no VNET integration. Access the storage account through the private link. The storage account should have at least two private links (file and blob).
2. Function App has no VNET integration and has one private endpoint.

Root Cause

The root cause of the issue was the inability of the Function App to establish a connection with the storage account due to the lack of network accessibility.

Solution

To resolve this, the Function App should be integrated into the Virtual Network (VNET), ensuring that the outbound configuration complies with the requirements to connect to the storage account through private endpoints.

Validation

This solution adheres to Azure best practices, utilising VNET integration with private endpoints to provide secure and private connectivity between the Function App and the storage account. The resolution can be validated by confirming the VNET configuration and verifying endpoint connectivity following the integration.

Basic Architecture Diagram