Invoking a lambda function from core device

Hi,

I am developing a device that does image classification on a Raspberry Pi after a user clicks a certain item on the touch screen menu. I liked the idea of using Greengrass to deploy the lambdas and models at scale and update them synchronously.

In my model, RPi is a core and I don't have any devices, as its camera is accessible as lambda is not containerised.

Currently I'm able to invoke the lambda function for classification from the IoT console with a MQTT message (basically, I followed the optimizedImageClassification tutorial). However, I don't understand if it is at all possible to invoke a lambda function from the core.

I was assuming I can just use invoke from aws-lambda, but it seems to be much more complicated. The only solutions I have found are related to assist in serverless development. I was also thinking of sending an MQTT request from the core to core but it seems to be unnecessarily complex.

Is there a right way to invoke lambdas from core device on user request? Or am I using the technology wrong? Thanks.