How to fix CORS + failed to load resource: net::err_failed happening only in the first request

Daniel 5

I have a frontend and backend both deployed on Azure app service.

The problem is the first request from the FE to the BE after some inactive time usually fails with the following errors,

User's image

The backend app logs don't show anything, it seems like the request didn't reach the backend. So maybe the backend is sleeping because of the inactivity? But why do we get the CORS error? I have configured CORS for the backend. To fix the sleeping issue, I have turned on the AlwaysOn feature and also added an availability ping that checks the health of the backend every 15 minutes, I thought that should make it available all the time.

Although the health pings are successful all the time, this request( which is much heavier than the health pings, involves sending images and detection using a model, and takes a fairly long time ) always fails on the first try and succeeds on subsequent requests.

Can someone help me with this?

Thanks in advance.

Ryan Hill 27,686 Reputation points Microsoft Employee

2024-03-05T00:50:42.4766667+00:00

Hey @Daniel, is it just your /api/buidlings-data that fails on initial request? Is there a different BE api endpoint that doesn't encounter this error or does it happen all the time regardless of endpoint?
Daniel 5 Reputation points

2024-03-05T06:38:54.1066667+00:00

Hi Ryan, thank you for the response. The others work just fine, it's only this endpoint.
Ryan Hill 27,686 Reputation points Microsoft Employee

2024-03-05T23:00:36.61+00:00

What HTTP verbs does /api/buidlings-data currently accept? I'm not saying it's a verb issue but I recall verbs causing CORS issues in the past.

Also, back to the sleep, you said the error happens on the initial request. If you make a request on a different uri, then hit this endpoint, do you still get the same error?
Ryan Hill 27,686 Reputation points Microsoft Employee

2024-03-13T14:29:37.6066667+00:00

Hey @Daniel, are you still seeing an issue? Were you able to get it resolved on your own?
Daniel 5 Reputation points

2024-03-14T14:24:35.63+00:00

Hi Ryan, yes it still happens.

and to answer your previous question, it also happens when I hit another endpoint first and come back
Ryan Hill 27,686 Reputation points Microsoft Employee

2024-03-19T23:09:35.2333333+00:00

@Daniel okay, so regardless, this particular endpoint results in this CORS error on the initial request? Subsequent requests are successful.
kasi selvam K 0 Reputation points

2024-08-27T10:24:07.08+00:00

same issue after updating to edge version 128.xx , getting

Failed to load resource: net::ERR_FAILED

as js resources not loaded in jsp files , due to which app breaks . do check .

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How to fix CORS + failed to load resource: net::err_failed happening only in the first request

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