Function App in Azure stopped working on May 6th

Hi @Pea Creamer ,

It looks like the root cause here was the Y1 (free/consumption-like) App Service plan being removed unexpectedly from your tenant. When that plan vanished on May 6th, your Function App had nowhere to run, so it went down until you re-provisioned on P2V3. Moving to P2V3 was the right call, but to be extra sure you won’t run into a similar surprise, here’s what I’d recommend:

1. Migrate to a supported App Service SKU

• Use at least a P1V3/P2V3 (or Premium/Elastic) plan. These SKUs won’t be removed without plenty of warning.
• Turn on Always On in Platform Features so your host stays warm and you avoid cold starts.

2. Monitor and size for memory usage

• Error codes 134 and 137 mean your process was OOM-killed. In Kudu you can inspect memory spikes under D:\home\LogFiles\Application\Functions or via Performance Counters in App Insights.
• In Application Insights, try a query against performanceCounters to see memory trends:

     performanceCounters  
     | where counterName == "\Process\Private Bytes" and timestamp > ago(1d)  

3. Keep your runtime supported

• You’re already on Functions Runtime v4 - perfect. If you ever need to change it, go to Configuration > Function runtime settings.

4. Use Application Insights and Activity Log for deep debugging

• To catch host-level restarts or config changes, run:

     traces  
     | where message contains "Host configuration has changed" or message contains "Signaling restart"  

• To surface errors at the outage time:

     traces  
     | where timestamp between (datetime(2023-05-06T00:00:00Z) .. datetime(2023-05-06T01:00:00Z))  
     | where severityLevel == "Error"  

5. Configure autoscale if your webshop has traffic bursts

• In your App Service Plan, set scale-out rules based on CPU or memory thresholds to add instances before you hit OOMs.

Hope this helps!

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Hello Pea Creamer,

Welcome to the Microsoft Q&A and thank you for posting your questions here.

I understand that your Function App in Azure stopped working on May 6th.

The Function App failed because the custom container didn’t become “ready” fast enough after a cold start, so the Azure platform’s startup/readiness checks timed out and the Functions host never finished initializing.

Follow the below procedures to resolve the issue:

1. Set the App Setting below to allow enough time for slow cold starts and make sure these core settings exist: WEBSITES_CONTAINER_START_TIME_LIMIT = 1800 FUNCTIONS_WORKER_RUNTIME = python FUNCTIONS_WORKER_RUNTIME is a standard app setting used by Azure Functions to determine the language worker (when applicable). If you’re using extension bundles (common for non-.NET apps), keep them on the supported v4 range:

      {
      "version": "2.0",
      "extensionBundle": {
       "id": "Microsoft.Azure.Functions.ExtensionBundle",
       "version": "[4.0.0, 5.0.0)"
      }
      }
   

   v4 is the active extension bundle line and is recommended for best reliability/supportability. This setting extends the maximum time the platform waits for your container to respond to warm-up/readiness pings before it restarts the container. - https://learn.microsoft.com/en-us/azure/app-service/reference-app-settings, https://learn.microsoft.com/en-us/troubleshoot/azure/app-service/faqs-app-service-linux-new NOTE: After changing app settings, restart the Function App to apply the change. https://learn.microsoft.com/en-us/azure/azure-functions/functions-app-settings
2. On Elastic Premium (EP), configure Always Ready / pre-warmed instances ≥ 1 so the app doesn’t drop to a full cold start state. This is one of the core Premium features designed to reduce cold starts. https://learn.microsoft.com/en-us/azure/azure-functions/functions-premium-plan, https://learn.microsoft.com/en-us/azure/azure-functions/functions-scale
3. Avoid shutting down the Function App nightly. Stopping the app forces a full cold start later, which increases the chance of hitting readiness/startup limits and delays host initialization. Premium plans are designed to run with at least one active instance anyway. - https://learn.microsoft.com/en-us/azure/azure-functions/functions-premium-plan, https://learn.microsoft.com/en-us/azure/app-service/reference-app-settings If cost control is the goal, use safer options such as: - lowering the minimum instance count (while keeping 1 warm instance if you need reliability) - autoscale rules, - right-sizing the EP SKU These approaches preserve availability and reduce the “cold start penalty.”
5. To reduce future cold start risk:
   • Shrink the image (multi-stage builds, slim base image, remove unused packages)
   • Move non-essential initialization out of startup (SDK warmups, cache loads, DB preloads) Microsoft also recommends keeping your Functions base image updated and maintained because containers are your responsibility in custom deployments. - https://learn.microsoft.com/en-us/azure/azure-functions/container-concepts, https://learn.microsoft.com/en-us/azure/azure-functions/functions-how-to-custom-container
6. Errors like “Custom storage volume(s) failed to initialize” often point to storage/network/DNS/SMB mount issues that can slow or block startup. Check:
   • Azure Files latency/availability
   • VNet integration + DNS resolution
   • Private Endpoint/firewall rules
   • SMB (445) reachability where applicable
   Functions on Premium commonly depend on Azure Files for content/host operations, so storage access issues can prevent the runtime from starting. - https://learn.microsoft.com/en-us/azure/azure-functions/storage-considerations, https://learn.microsoft.com/en-us/azure/azure-functions/functions-recover-storage-account
7. Turn on:
   • Application Insights / Azure Monitor logging
   • Function host logs AND container logs where available
   Application Insights is the primary supported way to collect function execution + host telemetry and troubleshoot initialization failures. - https://learn.microsoft.com/en-us/azure/azure-functions/configure-monitoring, https://learn.microsoft.com/en-us/azure/azure-functions/functions-app-settings

I hope this is helpful! Do not hesitate to let me know if you have any other questions or clarifications.

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