App service automatic scaling httplogs / application insights 404

Question

Dear all,

Need your help regarding the 404 errors logged because of azure app service automatisc scaling poller (visibly...)

Following the documentation, i'm not able to found the same entries (404 on / and 80).

The only one explained is /admin/host/ping but nothing shown :

https://learn.microsoft.com/en-us/azure/app-service/manage-automatic-scaling?tabs=azure-portal#why-does-appservicehttplogs-have-log-entries-similar-to-adminhostping-with-a-404-status

How to avoid that / rewrite or make the documentation up2 date ?it seems that ElasticScaleControllerExtension is related to premium Azure function;...(when googled it)

Answer 1

Hi Cloudy,
Thanks for reaching here!
The 404 errors you're seeing in your App Service logs are caused by Azure's automatic scaling poller, specifically the Elastic Scale Controller Extension (ElasticScaleControllerExtension/2.0.29.0). This is an internal Azure process that occasionally sends GET requests to check instance availability for auto-scaling.

These 404 responses are expected and do not impact scaling performance or security. Azure’s scaling decisions are based on CPU, memory, and response time, not these requests. The only status code that affects scaling is 429 (Too Many Requests), while scale-out decisions are primarily determined by latency.

Previously, this behavior was discussed when automatic scaling was in preview, but that is no longer the case. Microsoft has confirmed that these 404 errors are expected because the scaling monitor currently pings the same endpoint for both Function Apps and Web Apps. However, an upcoming release will modify this behavior by using a different endpoint for Web Apps, which should help reduce unnecessary logging.

At this time, there is no direct way to disable or rewrite these requests. If these logs are causing issues, you can filter them out in Application Insights to minimize noise. There is no security concern associated with these requests, as they originate from the same scale unit that hosts the app.

Health Check Endpoints in Azure App Service
https://learn.microsoft.com/en-us/answers/questions/1457153/seeing-a-lot-of-404s-to-admin-host-ping-after-turn
Filtering telemetry in Application Insights

https://stackoverflow.com/questions/79303286/most-recommended-approach-to-handle-404-errors-to-admin-host-ping-for-my-asp-ne
Let me know if you have any further assistances needed.
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