"Function host is not running" - Where do I find the error log?

Question

This is the second time I've ran into the "Function host is not running." error. Rather than just knowing a solution, I'd like to know the process for troubleshooting such a problem, in particular knowing where to go to obtain the underlying error.

The application has been redeployed today, and a HTTP trigger function has been tested. I've looked in the following places for error details (feel free to ask me to double check any of these if you know an error should be there, I'm only human!):

Diagnose and solve problems / Function App Down or Reporting Errors:

• Seems to be reporting a stale error, I even wrote code to terminate earlier with an exception and the original error still won't budge.

AppInsights:

• "Your app is offline or the Application Insights SDK needs updating."

Kudu:

• D:\home\LogFiles\eventlog.xml - Can't see anything meaningful here
• D:\home\LogFiles\Application\Functions\Function\FunctionName\*.log - No files for today
• D:\home\LogFiles\Application\Functions\Host\*.log - No files for today

Storage account file shares:

• One modified with today's date
  • /LogFiles/ - Empty
  • /site/wwwroot/ - Empty

Answer 1

There error should show in

Diagnose and solve problems / Function App Down or Reporting Errors

See answer to this question for more information.

Answer 2

Usually this error is caused by the invalid host.json file or an invalid proxies.json file.

Reference:

Function host is not running

host.json reference for Azure Functions 2.x and later.