Unable to determine handler from trigger event

Question

I am deploying back end application using python and fastapi. The application works fine. To warm up Lambda function , I created a rule with schedule of 1 min with JSON text { "hello": "test"} with my Lambda function as target. 
My fastapi example is as like
fastapi 0.71.0
mangum 0.12.3
```
from fastapi import FastAPI
from mangum import Mangum

app = FastAPI()
handler = Mangum(app)

@app.get("/ping")
def ping():
    return {'response': 'pong'}
```
Following error generates
```
[ERROR] TypeError: Unable to determine handler from trigger event
Traceback (most recent call last):
  File "/var/task/mangum/adapter.py", line 88, in __call__
    handler = AbstractHandler.from_trigger(
  File "/var/task/mangum/handlers/abstract_handler.py", line 115, in from_trigger
    raise TypeError("Unable to determine handler from trigger event")
[ERROR] TypeError: Unable to determine handler from trigger event Traceback (most recent call last):   File "/var/task/mangum/adapter.py", line 88, in __call__     handler = AbstractHandler.from_trigger(   File "/var/task/mangum/handlers/abstract_handler.py", line 115, in from_trigger     raise TypeError("Unable to determine handler from trigger event")
```

Answer

By default, the Lambda engine calls your function and is looking for an entry point like:

```
def lambda_handler(event, context):
    # your code goes here
````

You can see this when you create a new Python function.

If you're concerned about keeping your function warm, [Lambda provisioned concurrency](https://docs.aws.amazon.com/lambda/latest/dg/provisioned-concurrency.html) is normally a better way to go.

Answer

I recently faced a similar issue and the solution is provided at https://repost.aws/questions/QU0A9xe6i_T6CfOWLeiWm4XA/api-gateway-with-lambda-unable-to-import-module-server-no-module-named-server

An example of handler is located at https://github.com/fortejas/example-serverless-python-api/blob/main/lambda-api/server.py

```
handler = Mangum(app)
```
You would also need to install the required python dependencies

**Sample commands**
```
  curl -O https://bootstrap.pypa.io/get-pip.py
  sudo python3.7 get-pip.py 
  python -m pip --version 
  rm get-pip.py 
  pipenv
  cd lambda-api/
  virtualenv -p /usr/bin/python3.7 vpy37
  source vpy37/bin/activate
  pip3 install fastapi
  pip3 install boto3
  pip3 install Magnum
  pip3 install uvicorn
```

Unable to determine handler from trigger event

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