[BUG] warmupTrigger doesn't work as documented

[thomasfrederikhoeck]

Investigative information

Please provide the following:

• Timestamp: 2022-10-26
• Function App name:
• Function name(s) (as appropriate):
• Core Tools version: 3.0.4727

Repro steps

Provide the steps required to reproduce the problem:

1. Create a very basic function with a httpTriggerand a warmupTriggerfollowing the official guide https://learn.microsoft.com/en-us/azure/azure-functions/functions-bindings-warmup?tabs=in-process&pivots=programming-language-python:

## httptrigger/function.json
{
  "scriptFile": "__init__.py",
  "bindings": [
    {
      "authLevel": "function",
      "type": "httpTrigger",
      "direction": "in",
      "name": "req",
      "methods": [
        "post"
      ]
    },
    {
      "type": "http",
      "direction": "out",
      "name": "$return"
    }
  ]
}

## httptrigger/__init__.py
import logging
import azure.functions as func

async def main(req: func.HttpRequest) -> func.HttpResponse:
    logging.info("Succes!")
    return func.HttpResponse("Succes", status_code=200)

## warmup/function.json
{
    "bindings": [
        {
            "type": "warmupTrigger",
            "direction": "in",
            "name": "warmupContext"
        }
    ]
}

## warmup/__init__.py
import logging
import azure.functions as func

def main(warmupContext : func.Context) -> None:
    logging.warning('Function App instance is warm 🌞🌞🌞')

2. Run the function.
3. Get the following error:

   For detailed output, run func with --verbose flag.
   [2022-10-26T09:21:14.653Z] Worker process started and initialized.
   [2022-10-26T09:21:17.301Z] Host lock lease acquired by instance ID '0000000000000000000000002C1B88F1'.
   [2022-10-26T09:21:18.829Z] Worker failed to function id 65568825-e196-4213-9fc3-b55a123c4b89.
   [2022-10-26T09:21:18.831Z] Result: Failure
   Exception: FunctionLoadError: cannot load the warmup function: type of warmupContext binding in function.json "warmupTrigger" does not match its Python annotation "Context"
   Stack:   File "C:\Users\tfh\AppData\Roaming\npm\node_modules\azure-functions-core-tools\bin\workers\python\3.8/WINDOWS/X64\azure_functions_worker\dispatcher.py", line 320, in _handle__function_load_request   
   self._functions.add_function(
   File "C:\Users\tfh\AppData\Roaming\npm\node_modules\azure-functions-core-tools\bin\workers\python\3.8/WINDOWS/X64\azure_functions_worker\functions.py", line 217, in add_function
   raise FunctionLoadError(

If I try and remove the type it is never run which can be seen as this Exception is never hit

import azure.functions as func

def main(warmupContext) -> None:
    raise Exception('Function App instance is warm 🌞🌞🌞')

Expected behavior

Provide a description of the expected behavior.

It should locally when I run it as according to the guide

Support for the warmup trigger is provided by default in all development environments. You don't have to manually install the package or register the extension.

https://learn.microsoft.com/en-us/azure/azure-functions/functions-bindings-warmup?tabs=in-process&pivots=programming-language-python

Actual behavior

Provide a description of the actual behavior observed.

Raises the error:

For detailed output, run func with --verbose flag.
[2022-10-26T09:21:14.653Z] Worker process started and initialized.
[2022-10-26T09:21:17.301Z] Host lock lease acquired by instance ID '0000000000000000000000002C1B88F1'.
[2022-10-26T09:21:18.829Z] Worker failed to function id 65568825-e196-4213-9fc3-b55a123c4b89.
[2022-10-26T09:21:18.831Z] Result: Failure
Exception: FunctionLoadError: cannot load the warmup function: type of warmupContext binding in function.json "warmupTrigger" does not match its Python annotation "Context"
Stack:   File "C:\Users\tfh\AppData\Roaming\npm\node_modules\azure-functions-core-tools\bin\workers\python\3.8/WINDOWS/X64\azure_functions_worker\dispatcher.py", line 320, in _handle__function_load_request   
    self._functions.add_function(
  File "C:\Users\tfh\AppData\Roaming\npm\node_modules\azure-functions-core-tools\bin\workers\python\3.8/WINDOWS/X64\azure_functions_worker\functions.py", line 217, in add_function
    raise FunctionLoadError(

Known workarounds

Provide a description of any known workarounds.

Contents of the requirements.txt file:

Provide the requirements.txt file to help us find out module related issues.

azure-functions==1.8.0 

Related information

Provide any related information

• Links to source
• Bindings used

[thomasfrederikhoeck]

Hi @gavin-aguiar . I can see @vrdmr assigned you to this. Have you been able to replicate?

[thomasfrederikhoeck]

@gavin-aguiar @vrdmr is this actively worked on? :-)

[ramya894]

@thomasfrederikhoeck We are investigating on this will update you the findings soon.

[thomasfrederikhoeck]

@ramya894 sounds good!

[ramya894]

@thomasfrederikhoeck We are able to reproduce the problem and working on the solution to fix it. Thanks.

[gavin-aguiar]

Hi @thomasfrederikhoeck , apologies for the late response. We are looking into this error. In the mean time for mitigation, remove the type in the definition as you mentioned. Locally, you can invoke the warmup trigger by calling http://localhost:7071/admin/warmup. In Azure, the warmup trigger will be called only during scale out operations.

[thomasfrederikhoeck]

@gavin-aguiar Thank you. I have tried the work around and that works. However it still requires me to call the endpoint. Will the fix you have merged automatically call the warmup trigger when starting a local debug?

[YunchuWang]

@thomasfrederikhoeck Hi Thomas, in local the warmup trigger wont be automatically called. its only invoked by runtime in scaling scenarios, i.e in dedicated or elastic premium plans.

[thomasfrederikhoeck]

Gotcha. Then I think it would be meanigfull to show the endpoint in the startup messeage. In the following it is very hard to see that you need to call http://localhost:7071/admin/warmup to run it.