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Why is my Azure Function host permanently stopped?!

Azure Function forces the host to shut down if app_offline.htm is in your wwwroot folder

We were rolling out a new version of our Azure Function app which introduced durable Functions – It’s a great way to orchestrate multiple steps in a process across multiple functions.

Unfortunately, we’ve noticed that the Azure Function host was constantly shutting down. Interesting.

So I started the Azure Function diagnostics which is a great way to analyse what’s going on in terms of configuration et al.

No Key Vault references were broken, nothing was misconfigured and all our functions were correctly discovered – Hm, I was clueless.

When I came back in the office I’ve noticed that everything was back up and running, huh. It turns out my colleague Bjorn Baekelant found the issue – Once he deleted app_offline.htm from wwwroot it started up again!

I was pretty surprised to see that happening and it turns out that Azure Function forces the host to shut down if app_offline.htm is in your wwwroot folder.

For some reason, app_offline.htm was added to our folder which was the culprit. Once removed, everything was mitigated. Another lesson never to forget anymore.

Oh, and don’t ship things on Friday!

Thanks for reading,

Tom.

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