Azure Function stop working after deploy in one Environment.

Hi @Ranbir Sandhu

Thank you for reaching out to Microsoft Q&A.

This issue occurs because the Azure Functions runtime in the UAT environment is unable to successfully complete the “Sync Web Apps Function Triggers” operation after deployment. During trigger synchronization, the Functions host makes internal control‑plane calls to the Extensions API to load bindings, register triggers, and validate the runtime configuration. In UAT, these calls are returning 403 (Forbidden), which indicates that the runtime cannot reach one or more required platform endpoints (such as the storage account or management endpoints). This commonly happens when UAT has stricter networking controls (for example, Private Endpoints, VNet integration, disabled public network access, or storage firewalls). Even though the deployment succeeds and the app can write files such as host.json, trigger synchronization still fails, causing the Function App runtime to enter an Error state.

Refer below points to resolve this issue or use these as a workaround:

1. Verify AzureWebJobsStorage network access The trigger sync process must access the storage account defined in AzureWebJobsStorage. If the storage account has firewall rules or Private Endpoints enabled, ensure that the Function App can reach it.

• Temporarily enable public network access or allow trusted Microsoft services on the storage account.
• If using a Private Endpoint, confirm DNS resolution and that the Function App subnet can reach the storage endpoint.

2. Review Function App networking configuration Check whether the UAT Function App has Public Network Access disabled, VNet Integration enabled, or Private Endpoints configured. Trigger synchronization requires access to Azure platform endpoints (such as *.azurewebsites.net and storage endpoints).

• Temporarily enabling public network access can help confirm whether the issue is network‑related.
• If Private Endpoints are required, validate NSG rules and DNS configuration.

3. Restart the Function App and re‑sync triggers After correcting networking or access restrictions, restart the Function App (restart, not stop/start). This forces the runtime and Extensions host to reload configuration and reattempt trigger synchronization.

4. Compare with a working Function App in UAT Since other Function Apps in the same environment continue to work, compare their Networking and Storage access settings rather than ARM templates. Differences in firewall rules, Private Endpoints, or DNS configuration typically explain why only certain apps fail.Thank you for reaching out to Microsoft Q&A.

This issue occurs because the Azure Functions runtime in the UAT environment is unable to successfully complete the “Sync Web Apps Function Triggers” operation after deployment. During trigger synchronization, the Functions host makes internal control‑plane calls to the Extensions API to load bindings, register triggers, and validate the runtime configuration. In UAT, these calls are returning 403 (Forbidden), which indicates that the runtime cannot reach one or more required platform endpoints (such as the storage account or management endpoints). This commonly happens when UAT has stricter networking controls (for example, Private Endpoints, VNet integration, disabled public network access, or storage firewalls). Even though the deployment succeeds and the app can write files such as host.json, trigger synchronization still fails, causing the Function App runtime to enter an Error state.

Refer below points to resolve this issue or use these as a workaround:

1. Verify AzureWebJobsStorage network access
The trigger sync process must access the storage account defined in AzureWebJobsStorage. If the storage account has firewall rules or Private Endpoints enabled, ensure that the Function App can reach it.

• Temporarily enable public network access or allow trusted Microsoft services on the storage account.
• If using a Private Endpoint, confirm DNS resolution and that the Function App subnet can reach the storage endpoint.

2. Review Function App networking configuration
Check whether the UAT Function App has Public Network Access disabled, VNet Integration enabled, or Private Endpoints configured. Trigger synchronization requires access to Azure platform endpoints (such as *.azurewebsites.net and storage endpoints).

• Temporarily enabling public network access can help confirm whether the issue is network‑related.
• If Private Endpoints are required, validate NSG rules and DNS configuration.

3. Restart the Function App and re‑sync triggers
After correcting networking or access restrictions, restart the Function App (restart, not stop/start). This forces the runtime and Extensions host to reload configuration and reattempt trigger synchronization.

4. Compare with a working Function App in UAT
Since other Function Apps in the same environment continue to work, compare their Networking and Storage access settings rather than ARM templates. Differences in firewall rules, Private Endpoints, or DNS configuration typically explain why only certain apps fail.

The issue you're encountering with your Azure Functions in the UAT environment, where they report a runtime error and log an error message related to 'Sync Web Apps Function Triggers' with a status of 'Forbidden', could be attributed to several factors:

1. Permissions Issue: The 'Forbidden' error typically indicates that the Azure Functions do not have the necessary permissions to access certain resources or APIs. Ensure that the identity used by your Azure Functions in the UAT environment has the correct permissions assigned.
2. Configuration Differences: Check for any differences in configuration between your DEV and UAT environments. This includes connection strings, app settings, and any other environment-specific configurations that might affect the function's ability to run.
3. Networking Issues: If your UAT environment has different networking settings (like VNET integration or firewall rules), ensure that the Azure Functions can access the necessary resources without being blocked.
4. External Dependencies: If your functions rely on external services (like databases or APIs), verify that those services are accessible from the UAT environment and that any required credentials are correctly configured.

To resolve the issue, consider the following steps:

• Review the permissions for the Azure Functions in the UAT environment and adjust them as necessary.
• Compare the configuration settings between the DEV and UAT environments to identify any discrepancies.
• Check the networking setup to ensure that there are no restrictions preventing access to required resources.
• Investigate any external dependencies to ensure they are correctly configured and accessible.

If the issue persists, you may want to consult the Azure Function App Diagnostics tool for more insights into the problem.

References:

• Resolve common runtime issues after deployment
• Common scenarios, error messages, and symptoms