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Last Sunday one of our azure web apps went down for no obvious reason. There had been no code deployments for the past 5 days, the app was running fine on an S3 service level on a paid subscription. The only logical explanation I could come up was some VM being changed/upgraded underneath which caused our app to die.

After enabling the detailed error messages and logs through the stdout configuration in the web.config. I got to the following error:

"Could not load type 'System.Diagnostics.InjectedFunctionParent' from assembly 'System.Private.CoreLib'..."

Funny thing is we don't use such an assembly anywhere in our code...

We tried multiple solutions (re-deployment, scaling up and down the service plan, etc.) but the only one which worked was to delete the entire web app from azure and create it again...

Anyone bumped into a similar problem? How did you solve/prevent this?

Thanks in advance!

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  • i faced the same problem, nothing on the internet, i recreated a new app service. You saved my life. May 14, 2020 at 8:44

2 Answers 2

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We had the exact same thing happen. On Sunday one of our Azure web apps went down and when I enabled detailed error messages I got: Could not load type 'System.Diagnostics.InjectedFunctionParent' from assembly 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' because the parent does not exist.

Google brought up nothing and we also didn't have any deployments that week.

In our case the line of code which crashed the site was something that looped through the assemblies and loaded a list of types. I was able to fix the issue by excluding that assembly from the loop and deploying the new code. So I didn't need to re-create the web app which was my next idea.

I contacted Microsoft yesterday to see if they had any ideas or if any changes were made to app services but they said no changes were made.

So in conclusion I'm not really sure why it just started. My gut feel is there was a change to the app services or maybe extra logging/diagnostics has been enabled to some app services. (My other apps with similar code didn't crash)

Sorry I can't help more

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I suddenly had the same problem and was able to resolve it by disabling Application Insights, removing all configuration values relating to Application Insights and re-enabling it.

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