Is there any approach in azure that i can call different azure function based on the key present in azure service bus?

Question

I have service bus queue configured in azure which will trigger a azure function when a message has been sent.I want to leverage it , based on the key present in the Queue message , it should automatically trigger the different azure functions.

I have tried implementing this below Code :

import azure.functions as func
import logging
import json
app = func.FunctionApp()

@app.service_bus_queue_trigger(arg_name="azservicebus", queue_name="queue-asb",
                               connection="azuretopicnamespace_SERVICEBUS") 
def servicebus_queue_trigger(azservicebus: func.ServiceBusMessage):
    message_body = azservicebus.get_body().decode('utf-8')
    message_data = json.loads(message_body)
    if message_data.get('key_val','') =='service_bus_queue':
        print("Inside the if statment")
        result = service_bus_queue(azservicebus)
        print("Result",result)

    else:
        print("Inside the else statement")
        servicebus_trigger(azservicebus)


@app.service_bus_queue_trigger(arg_name="azservicebus", queue_name="queue-asb",
                               connection="azuretopicnamespace_SERVICEBUS") 
def service_bus_queue(azservicebus:func.ServiceBusMessage):
    a = 1+2
    print(a)
    print("This is the first function will be triggered")
    return a

@app.service_bus_queue_trigger(arg_name="azservicebus", queue_name="queue-asb",
                               connection="azuretopicnamespace_SERVICEBUS") 
def servicebus_trigger(azservicebus: func.ServiceBusMessage):
    print("This is the second function will be trigered")

I am not sure whether this is right approach or not ?

Answer 1

An Azure Function is invoked by a queue or subscription and you can't trigger a different function based on the payload since a function is always tied to a single entity.

Depending on how many keys you've got, you could use a fan out strategy, where you publish a message to a topic and have subscriptions that subscribe to the topic and filter out messages based on the keys. This approach will require the following.

1. Promote the key and its value to the message headers.
2. Subscribe to the topic and use a filter that's based on the key/value.
3. Have a function per subscription.

This approach is feasible for a small number of keys. If the number of keys is large, or it's dynamic in its nature, you'll need to have a different approach.