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We have our service hosted on App Service (Web Apps). And our runners are seeing 404 response status codes intermittently with and HTML page in the response sometimes. However, the requests have not been reaching our service.

From the logs available from App Service, I see thousands of 404s were output none being from the front end. However, on the worker logs I see only 8 of them and these other requests resulting in 404s hadn't reached our service. Attaching images from the logs:

App Service says all 404s resulted from workers

App Service says all 404s resulted from workers

App Service worker handler logs only show 8

App Service worker handler logs only show 8

The 8 404s we see in the worker logs were actually expected since we'd performed 8 negative tests to verify the 404s.

I'm trying to understand where these other 404s might be coming from. Any insight into why / how this could be happening would be super-helpful. Thanks!

slash
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  • Install application insights and look in there for the sources of your http requests – misha130 Apr 19 '22 at 21:39
  • Thank you for your response! I did check the App service logs but I can't account for about 200 404s that happened which seem to have not made it to the worker at all. Yet App Service says all were from the workers and none from the Frontend. I'm trying to understand if there's anything else in between – slash Apr 19 '22 at 22:10
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    Does this answer your question? [New deployed Azure web app is returning 404 Error code](https://stackoverflow.com/questions/69560100/new-deployed-azure-web-app-is-returning-404-error-code) –  Apr 20 '22 at 02:17
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    Could you please confirm if Always on is enabled check this blog might be helpful: https://devblogs.microsoft.com/premier-developer/404-response-code-caused-by-app-services-alwayson-feature/ – SnehaAgrawal-MSFT Apr 27 '22 at 10:19

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