Azure Event Hubs trigger and bindings for Azure Functions

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

Action	Type
Respond to events sent to an event hub event stream.	Trigger
Write events to an event stream	Output binding

Install extension

The extension NuGet package you install depends on the C# mode you're using in your function app:

Isolated worker model

Functions execute in an isolated C# worker process. To learn more, see Guide for running C# Azure Functions in an isolated worker process.

In-process model

Important

Support will end for the in-process model on November 10, 2026. We highly recommend that you migrate your apps to the isolated worker model for full support.

Functions execute in the same process as the Functions host. To learn more, see Develop C# class library functions using Azure Functions.

In a variation of this model, Functions can be run using C# scripting, which is supported primarily for C# portal editing. To update existing binding extensions for C# script apps running in the portal without having to republish your function app, see Update your extensions.

The functionality of the extension varies depending on the extension version:

Extension v5.x+

This section describes using a class library. For C# scripting, you would need to instead install the extension bundle, version 4.x.

This version introduces the ability to connect using an identity instead of a secret. For a tutorial on configuring your function apps with managed identities, see the creating a function app with identity-based connections tutorial.

This version uses the newer Event Hubs binding type Azure.Messaging.EventHubs.EventData.

This extension version is available by installing the NuGet package, version 5.x.

Extension v3.x+

This section describes using a class library. For C# scripting, you would need to instead install the extension bundle, version 2.x.

Supports the original Event Hubs binding parameter type of Microsoft.Azure.EventHubs.EventData.

Add the extension to your project by installing the NuGet package, version 3.x or 4.x.

Functions v1.x

Important

Support will end for version 1.x of the Azure Functions runtime on September 14, 2026. We highly recommend that you migrate your apps to version 4.x for full support.

Version 1.x of the Functions runtime doesn't require an extension.

Extension v5.x+

This version introduces the ability to connect using an identity instead of a secret. For a tutorial on configuring your function apps with managed identities, see the creating a function app with identity-based connections tutorial.

This version supports configuration of triggers and bindings through .NET Aspire integration.

Add the extension to your project by installing the NuGet package, version 5.x.

Extension v3.x+

Add the extension to your project by installing the NuGet package, version 4.x.

Functions v1.x

Version 1.x of the Functions runtime doesn't support running in an isolated worker process.

Install bundle

The Event Hubs extension is part of an extension bundle, which is specified in your host.json project file. You may need to modify this bundle to change the version of the binding, or if bundles aren't already installed. To learn more, see extension bundle.

This version introduces the ability to connect using an identity instead of a secret. For a tutorial on configuring your function apps with managed identities, see the creating a function app with identity-based connections tutorial.

You can add this version of the extension from the extension bundle v3 by adding or replacing the following code in your host.json file:

{
    "version": "2.0",
    "extensionBundle": {
        "id": "Microsoft.Azure.Functions.ExtensionBundle",
        "version": "[3.3.0, 4.0.0)"
    }
}

To learn more, see Update your extensions.

You can install this version of the extension in your function app by registering the extension bundle, version 2.x.

Version 1.x of the Functions runtime doesn't require extension bundles.

Binding types

The binding types supported for .NET depend on both the extension version and C# execution mode, which can be one of the following options:

Isolated worker model

An isolated worker process class library compiled C# function runs in a process isolated from the runtime.

In-process model

An in-process class library is a compiled C# function runs in the same process as the Functions runtime.

Choose a version to see binding type details for the mode and version.

Extension v5.x+

The Event Hubs extension supports parameter types according to the table below.

Binding scenario	Parameter types
Event Hubs trigger (single event)	Azure.Messaging.EventHubs.EventData JSON serializable types1 string byte[] [BinaryData]
Event Hubs trigger (batch of events)	EventData[] string[]
Event Hubs output (single event)	Azure.Messaging.EventHubs.EventData JSON serializable types1 string byte[] [BinaryData]
Event Hubs output (multiple events)	ICollector<T> or IAsyncCollector<T> where T is one of the single event types

¹ Events containing JSON data can be deserialized into known plain-old CLR object (POCO) types.

Extension v3.x+

Earlier versions of the extension exposed types from the now deprecated Microsoft.Azure.EventHubs namespace. Newer types from Azure.Messaging.EventHubs are exclusive to Extension v5.x+.

This version of the extension supports parameter types according to the table below.

Binding scenario	Parameter types
Event Hubs trigger (single message)	Microsoft.Azure.EventHubs.EventData JSON serializable types1 string byte[]
Event Hubs trigger (batch)	EventData[] string[]
Event Hubs output	Microsoft.Azure.EventHubs.EventData JSON serializable types1 string byte[]

¹ Events containing JSON data can be deserialized into known plain-old CLR object (POCO) types.

Functions v1.x

Earlier versions of the extension exposed types from the now deprecated Microsoft.Azure.EventHubs namespace. Newer types from Azure.Messaging.EventHubs are exclusive to Extension v5.x+.

This version of the extension supports parameter types according to the table below.

Binding scenario	Parameter types
Event Hubs trigger (single event)	Microsoft.Azure.EventHubs.EventData JSON serializable types1 string byte[]
Event Hubs trigger (batch of events)	EventData[] string[]
Event Hubs output	Microsoft.Azure.EventHubs.EventData JSON serializable types1 string byte[]

¹ Events containing JSON data can be deserialized into known plain-old CLR object (POCO) types.

Extension v5.x+

The isolated worker process supports parameter types according to the tables below. Support for binding to types from Azure.Messaging.EventHubs is in preview.

Event Hubs trigger

When you want the function to process a single event, the Event Hubs trigger can bind to the following types:

Type	Description
string	The event as a string. Use when the event is simple text.
byte[]	The bytes of the event.
JSON serializable types	When an event contains JSON data, Functions tries to deserialize the JSON data into a plain-old CLR object (POCO) type.
Azure.Messaging.EventHubs.EventData1	The event object. If you are migrating from any older versions of the Event Hubs SDKs, note that this version drops support for the legacy Body type in favor of EventBody.

When you want the function to process a batch of events, the Event Hubs trigger can bind to the following types:

Type	Description
string[]	An array of events from the batch, as strings. Each entry represents one event.
EventData[] 1	An array of events from the batch, as instances of Azure.Messaging.EventHubs.EventData. Each entry represents one event.
T[] where T is a JSON serializable type1	An array of events from the batch, as instances of a custom POCO type. Each entry represents one event.

¹ To use these types, you need to reference Microsoft.Azure.Functions.Worker.Extensions.EventHubs 5.5.0 or later and the common dependencies for SDK type bindings.

Event Hubs output binding

When you want the function to write a single event, the Event Hubs output binding can bind to the following types:

Type	Description
string	The event as a string. Use when the event is simple text.
byte[]	The bytes of the event.
JSON serializable types	An object representing the event. Functions tries to serialize a plain-old CLR object (POCO) type into JSON data.

When you want the function to write multiple events, the Event Hubs output binding can bind to the following types:

Type	Description
T[] where T is one of the single event types	An array containing multiple events. Each entry represents one event.

For other output scenarios, create and use an EventHubProducerClient with other types from Azure.Messaging.EventHubs directly. See Register Azure clients for an example of using dependency injection to create a client type from the Azure SDK.

Extension v3.x+

Earlier versions of the extension in the isolated worker process only support binding to strings and JSON serializable types. More options are available to Extension v5.x+.

Functions v1.x

Functions version 1.x doesn't support the isolated worker process. To use the isolated worker model, upgrade your application to Functions 4.x.

host.json settings

The host.json file contains settings that control behavior for the Event Hubs trigger. The configuration is different depending on the extension version.

Extension v5.x+

{
    "version": "2.0",
    "extensions": {
        "eventHubs": {
            "maxEventBatchSize" : 100,
            "minEventBatchSize" : 25,
            "maxWaitTime" : "00:05:00",            
            "batchCheckpointFrequency" : 1,
            "prefetchCount" : 300,
            "transportType" : "amqpWebSockets",
            "webProxy" : "https://proxyserver:8080",
            "customEndpointAddress" : "amqps://company.gateway.local",
            "targetUnprocessedEventThreshold" : 75,
            "initialOffsetOptions" : {
                "type" : "fromStart",
                "enqueuedTimeUtc" : ""
            },
            "clientRetryOptions":{
                "mode" : "exponential",
                "tryTimeout" : "00:01:00",
                "delay" : "00:00:00.80",
                "maximumDelay" : "00:01:00",
                "maximumRetries" : 3
            }
        }
    }
}  

Property	Default	Description
maxEventBatchSize2	100	The maximum number of events included in a batch for a single invocation. Must be at least 1.
minEventBatchSize1	1	The minimum number of events desired in a batch. The minimum applies only when the function is receiving multiple events and must be less than maxEventBatchSize. The minimum size isn't strictly guaranteed. A partial batch is dispatched when a full batch can't be prepared before the maxWaitTime has elapsed. Partial batches are also likely for the first invocation of the function after scaling takes place.
maxWaitTime1	00:01:00	The maximum interval that the trigger should wait to fill a batch before invoking the function. The wait time is only considered when minEventBatchSize is larger than 1 and is otherwise ignored. If less than minEventBatchSize events were available before the wait time elapses, the function is invoked with a partial batch. The longest allowed wait time is 10 minutes. NOTE: This interval is not a strict guarantee for the exact timing on which the function is invoked. There is a small margin of error due to timer precision. When scaling takes place, the first invocation with a partial batch may occur more quickly or may take up to twice the configured wait time.
batchCheckpointFrequency	1	The number of batches to process before creating a checkpoint for the event hub.
prefetchCount	300	The number of events that is eagerly requested from Event Hubs and held in a local cache to allow reads to avoid waiting on a network operation
transportType	amqpTcp	The protocol and transport that is used for communicating with Event Hubs. Available options: amqpTcp, amqpWebSockets
webProxy	null	The proxy to use for communicating with Event Hubs over web sockets. A proxy cannot be used with the amqpTcp transport.
customEndpointAddress	null	The address to use when establishing a connection to Event Hubs, allowing network requests to be routed through an application gateway or other path needed for the host environment. The fully qualified namespace for the event hub is still needed when a custom endpoint address is used, and it must be specified explicitly or via the connection string.
targetUnprocessedEventThreshold1	null	The desired number of unprocessed events per function instance. The threshold is used in target-based scaling to override the default scaling threshold inferred from the maxEventBatchSize option. When set, the total unprocessed event count is divided by this value to determine the number of function instances needed. The instance count is rounded up to a number that creates a balanced partition distribution.
initialOffsetOptions/type	fromStart	The location in the event stream to start processing when a checkpoint does not exist in storage. Applies to all partitions. For more information, see the OffsetType documentation. Available options: fromStart, fromEnd, fromEnqueuedTime
initialOffsetOptions/enqueuedTimeUtc	null	Specifies the enqueued time of the event in the stream from which to start processing. When initialOffsetOptions/type is configured as fromEnqueuedTime, this setting is mandatory. Supports time in any format supported by DateTime.Parse(), such as 2020-10-26T20:31Z. For clarity, you should also specify a timezone. When timezone isn't specified, Functions assumes the local timezone of the machine running the function app, which is UTC when running on Azure.
clientRetryOptions/mode	exponential	The approach to use for calculating retry delays. Exponential mode retries attempts with a delay based on a back-off strategy where each attempt will increase the duration that it waits before retrying. The fixed mode retries attempts at fixed intervals with each delay having a consistent duration. Available options: exponential, fixed
clientRetryOptions/tryTimeout	00:01:00	The maximum duration to wait for an Event Hubs operation to complete, per attempt.
clientRetryOptions/delay	00:00:00.80	The delay or back-off factor to apply between retry attempts.
clientRetryOptions/maximumDelay	00:00:01	The maximum delay to allow between retry attempts.
clientRetryOptions/maximumRetries	3	The maximum number of retry attempts before considering the associated operation to have failed.

¹ Using minEventBatchSize and maxWaitTime requires v5.3.0 of the Microsoft.Azure.WebJobs.Extensions.EventHubs package, or a later version.

² The default maxEventBatchSize changed in v6.0.0 of the Microsoft.Azure.WebJobs.Extensions.EventHubs package. In earlier versions, this was 10.

The clientRetryOptions are used to retry operations between the Functions host and Event Hubs (such as fetching events and sending events). Refer to guidance on Azure Functions error handling and retries for information on applying retry policies to individual functions.

For a reference of host.json in Azure Functions 2.x and beyond, see host.json reference for Azure Functions.

Extension v3.x+

{
    "version": "2.0",
    "extensions": {
        "eventHubs": {
            "batchCheckpointFrequency": 1,
            "eventProcessorOptions": {
                "maxBatchSize": 256,
                "prefetchCount": 512
            },
            "initialOffsetOptions": {
                "type": "fromStart",
                "enqueuedTimeUtc": ""
            }
        }
    }
}  

Property	Default	Description
batchCheckpointFrequency	1	The number of event batches to process before creating an Event Hubs cursor checkpoint.
eventProcessorOptions/maxBatchSize	10	The maximum event count received per receive loop.
eventProcessorOptions/prefetchCount	300	The default prefetch count used by the underlying EventProcessorHost. The minimum allowed value is 10.
initialOffsetOptions/type1	fromStart	The location in the event stream from which to start processing when a checkpoint doesn't exist in storage. Options are fromStart , fromEnd or fromEnqueuedTime. fromEnd processes new events that were enqueued after the function app started running. Applies to all partitions. For more information, see the EventProcessorOptions documentation.
initialOffsetOptions/enqueuedTimeUtc1	null	Specifies the enqueued time of the event in the stream from which to start processing. When initialOffsetOptions/type is configured as fromEnqueuedTime, this setting is mandatory. Supports time in any format supported by DateTime.Parse(), such as 2020-10-26T20:31Z. For clarity, you should also specify a timezone. When timezone isn't specified, Functions assumes the local timezone of the machine running the function app, which is UTC when running on Azure. For more information, see the EventProcessorOptions documentation.

¹ Support for initialOffsetOptions begins with EventHubs v4.2.0.

For a reference of host.json in Azure Functions 2.x and beyond, see host.json reference for Azure Functions.

Functions v1.x

{
    "eventHub": {
      "maxBatchSize": 64,
      "prefetchCount": 256,
      "batchCheckpointFrequency": 1
    }
}

Property	Default	Description
maxBatchSize	64	The maximum event count received per receive loop.
prefetchCount	300	The default prefetch that will be used by the underlying EventProcessorHost.
batchCheckpointFrequency	1	The number of event batches to process before creating an Event Hubs cursor checkpoint.

For a reference of host.json in Azure Functions 1.x, see host.json reference for Azure Functions 1.x.

Next steps

• Respond to events sent to an event hub event stream (Trigger)
• Write events to an event stream (Output binding)