title	description	ms.assetid	ms.topic	ms.custom	ms.date	zone_pivot_groups
Azure Event Hubs output binding for Azure Functions	Learn to write messages to Azure Event Hubs streams using Azure Functions.	daf81798-7acc-419a-bc32-b5a41c6db56b	reference	devx-track-extended-java, devx-track-js, devx-track-python, devx-track-ts	03/03/2023	programming-languages-set-functions

Azure Event Hubs output binding for Azure Functions

This article explains how to work with Azure Event Hubs bindings for Azure Functions. Azure Functions supports trigger and output bindings for Event Hubs.

For information on setup and configuration details, see the overview.

Use the Event Hubs output binding to write events to an event stream. You must have send permission to an event hub to write events to it.

Make sure the required package references are in place before you try to implement an output binding.

::: zone pivot="programming-language-javascript,programming-language-typescript" [!INCLUDE functions-nodejs-model-tabs-description] ::: zone-end ::: zone pivot="programming-language-python" [!INCLUDE functions-bindings-python-models-intro]

::: zone-end

Example

::: zone pivot="programming-language-csharp"

Isolated worker model

The following example shows a C# function that writes a message string to an event hub, using the method return value as the output:

:::code language="csharp" source="~/azure-functions-dotnet-worker/samples/Extensions/EventHubs/EventHubsFunction.cs" range="20-31":::

In-process model

[!INCLUDE functions-in-process-model-retirement-note]

The following example shows a C# function that writes a message to an event hub, using the method return value as the output:

[FunctionName("EventHubOutput")]
[return: EventHub("outputEventHubMessage", Connection = "EventHubConnectionAppSetting")]
public static string Run([TimerTrigger("0 */5 * * * *")] TimerInfo myTimer, ILogger log)
{
    log.LogInformation($"C# Timer trigger function executed at: {DateTime.Now}");
    return $"{DateTime.Now}";
}

The following example shows how to use the IAsyncCollector interface to send a batch of messages. This scenario is common when you are processing messages coming from one event hub and sending the result to another event hub.

[FunctionName("EH2EH")]
public static async Task Run(
    [EventHubTrigger("source", Connection = "EventHubConnectionAppSetting")] EventData[] events,
    [EventHub("dest", Connection = "EventHubConnectionAppSetting")]IAsyncCollector<EventData> outputEvents,
    ILogger log)
{
    foreach (EventData eventData in events)
    {
        // Do some processing:
        string newEventBody = DoSomething(eventData);
        
        // Queue the message to be sent in the background by adding it to the collector.
        // If only the event is passed, an Event Hubs partition to be assigned via
        // round-robin for each batch.
        await outputEvents.AddAsync(new EventData(newEventBody));
        
        // If your scenario requires that certain events are grouped together in an
        // Event Hubs partition, you can specify a partition key.  Events added with 
        // the same key will always be assigned to the same partition.        
        await outputEvents.AddAsync(new EventData(newEventBody), "sample-key");
    }
}

::: zone-end ::: zone pivot="programming-language-typescript"

Model v4

The following example shows a timer triggered TypeScript function that sends a single message to an event hub:

:::code language="typescript" source="~/azure-functions-nodejs-v4/ts/src/functions/eventHubOutput1.ts" :::

To output multiple messages, return an array instead of a single object. For example:

:::code language="typescript" source="~/azure-functions-nodejs-v4/ts/src/functions/eventHubOutput2.ts" id="displayInDocs" :::

Model v3

TypeScript samples are not documented for model v3.

::: zone-end
::: zone pivot="programming-language-javascript"

Model v4

The following example shows a timer triggered JavaScript function that sends a single message to an event hub:

:::code language="javascript" source="~/azure-functions-nodejs-v4/js/src/functions/eventHubOutput1.js" :::

To output multiple messages, return an array instead of a single object. For example:

:::code language="javascript" source="~/azure-functions-nodejs-v4/js/src/functions/eventHubOutput2.js" id="displayInDocs" :::

Model v3

The following example shows an event hub trigger binding in a function.json file and a function that uses the binding. The function writes an output message to an event hub.

The following example shows an Event Hubs binding data in the function.json file, which is different for version 1.x of the Functions runtime compared to later versions.

{
    "type": "eventHub",
    "name": "outputEventHubMessage",
    "eventHubName": "myeventhub",
    "connection": "MyEventHubSendAppSetting",
    "direction": "out"
}

Here's JavaScript code that sends a single message:

module.exports = function (context, myTimer) {
    var timeStamp = new Date().toISOString();
    context.log('Message created at: ', timeStamp);   
    context.bindings.outputEventHubMessage = "Message created at: " + timeStamp;
    context.done();
};

Here's JavaScript code that sends multiple messages:

module.exports = function(context) {
    var timeStamp = new Date().toISOString();
    var message = 'Message created at: ' + timeStamp;

    context.bindings.outputEventHubMessage = [];

    context.bindings.outputEventHubMessage.push("1 " + message);
    context.bindings.outputEventHubMessage.push("2 " + message);
    context.done();
};

::: zone-end
::: zone pivot="programming-language-powershell"

Complete PowerShell examples are pending. ::: zone-end ::: zone pivot="programming-language-python"
The following example shows an event hub trigger binding and a Python function that uses the binding. The function writes a message to an event hub. The example depends on whether you use the v1 or v2 Python programming model.

v2

import logging
import azure.functions as func

app = func.FunctionApp()

@app.function_name(name="eventhub_output")
@app.route(route="eventhub_output")
@app.event_hub_output(arg_name="event",
                      event_hub_name="<EVENT_HUB_NAME>",
                      connection="<CONNECTION_SETTING>")
def eventhub_output(req: func.HttpRequest, event: func.Out[str]):
    body = req.get_body()
    if body is not None:
        event.set(body.decode('utf-8'))
    else:    
        logging.info('req body is none')
    return 'ok'

Here's Python code that sends multiple messages:

import logging
import azure.functions as func
from typing import List

app = func.FunctionApp()

@app.function_name(name="eventhub_output")
@app.route(route="eventhub_output")
@app.event_hub_output(arg_name="event",
                      event_hub_name="<EVENT_HUB_NAME>",
                      connection="<CONNECTION_SETTING>")

def eventhub_output(req: func.HttpRequest, event: func.Out[List[str]]) -> func.HttpResponse:
    my_messages=["message1", "message2","message3"]
    event.set(my_messages)
    return func.HttpResponse(f"Messages sent")

v1

The following examples show Event Hubs binding data in the function.json file.

{
    "type": "eventHub",
    "name": "$return",
    "eventHubName": "myeventhub",
    "connection": "MyEventHubSendAppSetting",
    "direction": "out"
}

Here's Python code that sends a single message:

import datetime
import logging
import azure.functions as func


def main(timer: func.TimerRequest) -> str:
    timestamp = datetime.datetime.utcnow()
    logging.info('Message created at: %s', timestamp)
    return 'Message created at: {}'.format(timestamp)

Here's Python code that sends multiple messages:

import logging
from typing import List
import azure.functions as func


def main(req: func.HttpRequest, messages:func.Out[List[str]]) -> func.HttpResponse:
    logging.info('Python HTTP trigger function processed a request.')
    messages.set([{"message1"}, {"message2"}])
    return func.HttpResponse(f"Messages sent")

::: zone-end ::: zone pivot="programming-language-java" The following example shows a Java function that writes a message containing the current time to an event hub.

@FunctionName("sendTime")
@EventHubOutput(name = "event", eventHubName = "samples-workitems", connection = "AzureEventHubConnection")
public String sendTime(
   @TimerTrigger(name = "sendTimeTrigger", schedule = "0 */5 * * * *") String timerInfo)  {
     return LocalDateTime.now().toString();
 }

In the Java functions runtime library, use the @EventHubOutput annotation on parameters whose value would be published to Event Hubs. The parameter should be of type OutputBinding<T> , where T is a POJO or any native Java type.

::: zone-end ::: zone pivot="programming-language-csharp"

Attributes

Both in-process and isolated worker process C# libraries use attribute to configure the binding. C# script instead uses a function.json configuration file as described in the C# scripting guide.

Isolated worker model

Use the [EventHubOutputAttribute] to define an output binding to an event hub, which supports the following properties.

Parameters	Description
EventHubName	The name of the event hub. When the event hub name is also present in the connection string, that value overrides this property at runtime.
Connection	The name of an app setting or setting collection that specifies how to connect to Event Hubs. To learn more, see Connections.

In-process model

Use the EventHubAttribute to define an output binding to an event hub, which supports the following properties.

Parameters	Description
EventHubName	The name of the event hub. When the event hub name is also present in the connection string, that value overrides this property at runtime.
Connection	The name of an app setting or setting collection that specifies how to connect to Event Hubs. To learn more, see Connections.

::: zone-end
::: zone pivot="programming-language-python"

Decorators

Applies only to the Python v2 programming model.

For Python v2 functions defined using a decorator, these properties are supported for event_hub_output:

Property	Description
`arg_name`	The variable name used in function code that represents the event.
`event_hub_name`	he name of the event hub. When the event hub name is also present in the connection string, that value overrides this property at runtime.
`connection`	The name of an app setting or setting collection that specifies how to connect to Event Hubs. To learn more, see Connections.

For Python functions defined by using function.json, see the Configuration section. ::: zone-end

::: zone pivot="programming-language-java"

Annotations

In the Java functions runtime library, use the EventHubOutput annotation on parameters whose value would be published to Event Hubs. The following settings are supported on the annotation:

name
dataType
eventHubName
connection

::: zone-end ::: zone pivot="programming-language-javascript,programming-language-typescript,programming-language-python,programming-language-powershell"

Configuration

::: zone-end

::: zone pivot="programming-language-python" Applies only to the Python v1 programming model.

::: zone-end ::: zone pivot="programming-language-javascript,programming-language-typescript"

Model v4

The following table explains the properties that you can set on the options object passed to the output.eventHub() method.

Property	Description
eventHubName	The name of the event hub. When the event hub name is also present in the connection string, that value overrides this property at runtime.
connection	The name of an app setting or setting collection that specifies how to connect to Event Hubs. To learn more, see Connections.

Model v3

The following table explains the binding configuration properties that you set in the function.json file.

Property	Description
type	Must be set to `eventHub`.
direction	Must be set to `out`. This parameter is set automatically when you create the binding in the Azure portal.
name	The variable name used in function code that represents the event.
eventHubName	The name of the event hub. When the event hub name is also present in the connection string, that value overrides this property at runtime.
connection	The name of an app setting or setting collection that specifies how to connect to Event Hubs. To learn more, see Connections.

::: zone-end ::: zone pivot="programming-language-powershell,programming-language-python"

The following table explains the binding configuration properties that you set in the function.json file, which differs by runtime version.

Functions 2.x+

function.json property	Description
type	Must be set to `eventHub`.
direction	Must be set to `out`. This parameter is set automatically when you create the binding in the Azure portal.
name	The variable name used in function code that represents the event.
eventHubName	Functions 2.x and higher. The name of the event hub. When the event hub name is also present in the connection string, that value overrides this property at runtime.
connection	The name of an app setting or setting collection that specifies how to connect to Event Hubs. To learn more, see Connections.

Functions 1.x

function.json property	Description
type	Must be set to `eventHub`.
direction	Must be set to `out`. This parameter is set automatically when you create the binding in the Azure portal.
name	The variable name used in function code that represents the event.
path	Functions 1.x only. The name of the event hub. When the event hub name is also present in the connection string, that value overrides this property at runtime.
connection	The name of an app setting or setting collection that specifies how to connect to Event Hubs. To learn more, see Connections.

::: zone-end

[!INCLUDE app settings to local.settings.json]

Usage

::: zone pivot="programming-language-csharp"
The parameter type supported by the Event Hubs output binding depends on the Functions runtime version, the extension package version, and the C# modality used.

Extension v5.x+

In-process C# class library functions supports the following types:

Azure.Messaging.EventHubs.EventData
String
Byte array
Plain-old CLR object (POCO)

This version of EventData drops support for the legacy Body type in favor of EventBody.

Send messages by using a method parameter such as out string paramName. To write multiple messages, you can use ICollector<EventData> or IAsyncCollector<EventData> in place of out string. Partition keys may only be used with IAsyncCollector<EventData>.

Extension v3.x+

In-process C# class library functions supports the following types:

Microsoft.Azure.EventHubs.EventData
String
Byte array
Plain-old CLR object (POCO)

Send messages by using a method parameter such as out string paramName. To write multiple messages, you can use ICollector<string> or IAsyncCollector<string> in place of out string.

Extension v5.x+

[!INCLUDE functions-bindings-event-hubs-output-dotnet-isolated-types]

Extension v3.x+

Requires you to define a custom type, or use a string. Additional options are available in Extension v5.x+.

::: zone-end
::: zone pivot="programming-language-java"

There are two options for outputting an Event Hubs message from a function by using the EventHubOutput annotation:

Return value: By applying the annotation to the function itself, the return value of the function is persisted as an Event Hubs message.
Imperative: To explicitly set the message value, apply the annotation to a specific parameter of the type OutputBinding<T>, where T is a POJO or any native Java type. With this configuration, passing a value to the setValue method persists the value as an Event Hubs message. ::: zone-end ::: zone pivot="programming-language-powershell"

Complete PowerShell examples are pending. ::: zone-end ::: zone pivot="programming-language-javascript,programming-language-typescript"

Model v4

Access the output message by returning the value directly or using context.extraOutputs.set().

Model v3

Access the output event by using context.bindings.<name> where <name> is the value specified in the name property of function.json.

::: zone-end
::: zone pivot="programming-language-python"

There are two options for outputting an Event Hubs message from a function:

Return value: Set the name property in function.json to $return. With this configuration, the function's return value is persisted as an Event Hubs message.
Imperative: Pass a value to the set method of the parameter declared as an Out type. The value passed to set is persisted as an Event Hubs message.

::: zone-end

[!INCLUDE functions-event-hubs-connections]

Exceptions and return codes

Binding	Reference
Event Hubs	Operations Guide

Next steps

Respond to events sent to an event hub event stream (Trigger)

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functions-bindings-event-hubs-output.md

functions-bindings-event-hubs-output.md

Azure Event Hubs output binding for Azure Functions

Example

Isolated worker model

In-process model

Model v4

Model v3

Model v4

Model v3

v2

v1

Attributes

Isolated worker model

In-process model

Decorators

Annotations

Configuration

Model v4

Model v3

Functions 2.x+

Functions 1.x

Usage

Extension v5.x+

Extension v3.x+

Extension v5.x+

Extension v3.x+

Model v4

Model v3

Exceptions and return codes

Next steps

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Azure Event Hubs output binding for Azure Functions

Example

Attributes

Decorators

Annotations

Configuration

Usage

Exceptions and return codes

Next steps