Multiple Azure EventHub trigger to single function in Azure Function app

Question

I want to do the same functionality (with few changes based on message data) from two different eventhubs.

Is it possible to attach two consumer group to a single function.

It did not work even though I add it to function.json.

Answer 1

The short answer is no. You cannot bind multiple input triggers to the same function: https://github.com/Azure/azure-webjobs-sdk-script/wiki/function.json

A function can only have a single trigger binding, and can have multiple input/output bindings.

However, you can call the same "shared" code from multiple functions by either wrapping the shared code in a helper method, or using Precompiled Functions.

Answer 2

Recommended practice here is to share business logic between functions by using the fact that a single function app can be composed of multiple functions.

MyFunctionApp
|     host.json
|____ business
|     |____ logic.js
|____ function1
|     |____ index.js
|     |____ function.json
|____ function2
      |____ index.js
      |____ function.json

In "function1/index.js" and "function2/index.js"

var logic = require("../business/logic");

module.exports = logic;

The function.json of function1 and function2 can be configured to different triggers.

In "business/logic.js

module.exports = function (context, req) {
    // This is where shared code goes. As an example, for an HTTP trigger:
    context.res = {
        body: "<b>Hello World</b>",
        status: 201,
        headers: {
            'content-type': "text/html"
        }
    };     
    context.done();
};

Answer 3

Is it possible to attach two consumer group to a single function.

Assuming you're looking for trigger and don't want to do your own polling using EventProcessorClient inside your function. Because you can schedule a function to periodically use API to fetch messages from multiple event hubs and process them. But you need to implement all the built-in logic (polling, handling multiple partitions, check-pointing, scaling, ...) you get when you use triggers.

Couple of work arounds:

1. Capture: If event hubs are in same namespace, you can enable capture on all your event hubs. Then create an event grid trigger for your function. You'll get a message with path of capture file. E.g.

{
    "topic": "/subscriptions/9fac-4e71-9e6b-c0fa7b159e78/resourcegroups/kash-test-01/providers/Microsoft.EventHub/namespaces/eh-ns",
    "subject": "eh-1",
    "eventType": "Microsoft.EventHub.CaptureFileCreated",
    "id": "b5aa3f62-15a1-497a-b97b-e688d4368db8",
    "data": {
        "fileUrl": "https://xxx.blob.core.windows.net/capture-fs/eh-ns/eh-1/0/2020/10/28/21/39/01.avro",
        "fileType": "AzureBlockBlob",
        "partitionId": "0",
        "sizeInBytes": 8011,
        "eventCount": 5,
        "firstSequenceNumber": 5,
        "lastSequenceNumber": 9,
        "firstEnqueueTime": "2020-10-28T21:40:28.83Z",
        "lastEnqueueTime": "2020-10-28T21:40:28.908Z"
    },
    "dataVersion": "1",
    "metadataVersion": "1",
    "eventTime": "2020-10-28T21:41:02.2472744Z"
}

Obviously this is not real-time, min capture time you can set is 1 minute and there might be a little delay between the time captured avro file is written and your function is invoked.

2. At least in Java there is no restriction that you must have a separate class for each function. So you can do this:

public class EhConsumerFunctions {
    private void processEvent(String event) {
        // process...
    }

    @FunctionName("eh1_consumer")
    public void eh1_consumer(
        @EventHubTrigger(name = "event", eventHubName = "eh-ns", connection = "EH1_CONN_STR") String event,
        final ExecutionContext context) {
        processEvent(event);
    }

    @FunctionName("eh2_consumer")
    public void eh2_consumer(
        @EventHubTrigger(name = "event", eventHubName = "eh-ns", connection = "EH2_CONN_STR") String event,
        final ExecutionContext context) {
        processEvent(event);
    }

}

and define EH1_CONN_STR and EH2_CONN_STR in your app settings.