Azure Functions Documentation

Event Hub Output Bindings

This document describes how to configure and use output bindings for Azure Event Hubs in Azure Functions.

Overview

Event Hub output bindings allow your Azure Function to send messages to an Azure Event Hub. This is useful for scenarios where your function processes data and needs to emit it to a stream for further processing, analytics, or archival.

Configuration

Output bindings are configured in your function's function.json file (for JavaScript, C#, and other non-Python languages) or using decorators in Python.

function.json Example

{
  "bindings": [
    {
      "name": "msg",
      "type": "eventHubOutput",
      "direction": "out",
      "eventHubName": "my-event-hub",
      "connection": "EventHubConnectionString"
    }
  ]
}

Python Decorator Example

import azure.functions as func

def main(myInput: func.EventGridEvent, msg: func.Out[str]):
    msg.set("Hello from Event Hub output binding!")

Using the Output Binding

The output binding is represented by a variable in your function code. You can then set a value on this variable, which will be sent as a message to the configured Event Hub.

JavaScript Example

module.exports = async function (context, req) {
    context.log('JavaScript HTTP trigger function processed a request.');

    const message = req.body && req.body.message ? req.body.message : "Default message";

    context.bindings.msg = message; // Set the message to the output binding

    context.res = {
        status: 200,
        body: "Message sent to Event Hub"
    };
};

C# Example

using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.Http;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;

public static class EventHubOutputFunction
{
    [FunctionName("SendToEventHub")]
    public static void Run(
        [HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)] HttpRequest req,
        [EventHub("my-event-hub", Connection = "EventHubConnectionString")] out string msg,
        ILogger log)
    {
        log.LogInformation("C# HTTP trigger function processed a request.");

        string messageToSend = "Hello from C# Azure Function!";
        msg = messageToSend; // Assign the message to the output binding

        log.LogInformation($"Message sent to Event Hub: {messageToSend}");
    }
}

Message Formatting

The output binding typically accepts a string. For complex data structures, you'll want to serialize them into JSON strings before sending.

Common Scenarios

• Data Streaming: Process incoming data (e.g., from IoT devices) and publish transformed or aggregated data to Event Hubs.
• Event Aggregation: Collect events from various sources and send them in batches to Event Hubs for centralized processing.
• Logging and Auditing: Send operational logs or audit trails to Event Hubs for consumption by monitoring tools.

Troubleshooting

If you encounter issues:

• Verify the EventHubConnectionString application setting is correctly configured and has the necessary permissions.
• Ensure the eventHubName matches the name of your Event Hub.
• Check Azure Monitor logs for any errors related to your function or Event Hub integration.

For more advanced scenarios, such as sending batched messages or handling errors, refer to the official Azure Functions documentation.