Python function suddenly stopped working without any code or resource changes

Hi @Dennis Admin ,

Thanks for reaching out to Microsoft Q&A.

It looks like your Python Durable Function host isn’t coming up and in your health checks you see

“azure.functions.script_host.lifecycle”: {“status”: “Unhealthy”, “description”: “No script host available”}

That means the Functions runtime worker never actually started.

Here’s a structured way to pinpoint what’s going on:

1. Check host‐startup exceptions
   • If you have Application Insights enabled, run this query to see if the host is failing at startup:

          
          exceptions
          
          | where customDimensions.Category == "Host.Startup"
          
     

   • If you’re using a Log Analytics workspace, pull your Function App console logs:

          
          AppServiceConsoleLogs_CL
          
          | where AppName_s =~ "*<YourFunctionAppName>*"
          
          | where Log_s contains "ErrorOccuredDuringStartupOperation"
          
     

   Look for errors or stack traces that indicate the Python worker crashed (e.g. WorkerProcessExitException, python exited with code 139).
2. Verify your runtime and Python versions
   • On a Flex Consumption plan, only certain Python versions and Functions runtime versions are supported.
   • In the Azure portal go to Configuration → General settings and confirm: • FUNCTIONS_EXTENSION_VERSION (should be ~4 for Python 3.9) • Python version (3.9 is generally the supported default right now on Flex)
   If Azure rolled out an update that bumped you to a newer worker (e.g. v4 host targeting Python 3.10) and your code or native dependencies aren’t ready, the host can fail immediately.
3. Look for segmentation faults or native‐library issues
   • If your logs show a python exited with code 139, that’s typically a SIGSEGV in a C extension.
   • Check your requirements.txt for any unpinned packages that might have auto-upgraded overnight. Pin versions or temporarily remove suspect packages to see if the worker starts.
4. Confirm storage connectivity
   • The script host needs an AzureWebJobsStorage connection. If your storage account has new firewall rules or the connection string was rotated outside of your resources, the host can’t initialize.
   • Double-check that the AzureWebJobsStorage setting in Configuration is still valid and that the storage account is reachable.
5. Restart and redeploy
   • Sometimes forcing a redeploy or doing a manual restart (Platform features → Development Tools → Restart) can clear a hung worker.
   • If you suspect a platform bug, you can pin the host version in host.json:

          
          {
          
          "version": "2.0",
          
          "extensionBundle": {
          
          "id": "Microsoft.Azure.Functions.ExtensionBundle",
          
          "version": "[2.*, 3.0.0)"
          
          }
          
          }
     

Hi @Pravallika KV

Thanks for getting back to me.

Please find below answers to your suggestions.

1. Application returns nothing.
2. The FUNCTIONS_EXTENSION_VERSION value is not available under my function app
3. Returned no results
4. The connection string under AzureWebJobsStorage is valid.
5. Tried that a few times. The deployment fails on "Checking the app health...Host status endpoint" after 15 tries. In one odd occasion, the deploy completed after struggling for 11 o15 reties and the functions were listed, but when returning to the Functions portal, nothing is running.
6. The function app already have the below in its host.json

      
      "extensionBundle": {
          "id": "Microsoft.Azure.Functions.ExtensionBundle",
          "version": "[4.*, 5.0.0)"
        }
   

Thanks for the confirmation @Dennis Admin . I reached out to you over private message, could you please check and share the requested information?

Hi @Pravallika KVJust following up on the private message. I have not received anything from you yet.

Regards

Dennis

Hi @Pravallika KV

Just following up on the private message. I have not received anything from you yet.

Regards

Dennis