title	description	ms.topic	ms.date	ms.devlang	ms.custom	zone_pivot_groups
Azure Queue storage trigger for Azure Functions	Learn to run an Azure Function as Azure Queue storage data changes.	reference	04/04/2023	csharp, java, javascript, powershell, python	devx-track-csharp, cc996988-fb4f-47, devx-track-python, devx-track-extended-java, devx-track-js	programming-languages-set-functions-lang-workers

Azure Queue storage trigger for Azure Functions

The queue storage trigger runs a function as messages are added to Azure Queue storage.

Azure Queue storage scaling decisions for the Consumption and Premium plans are done via target-based scaling. For more information, see Target-based scaling.

::: zone pivot="programming-language-python"
Azure Functions supports two programming models for Python. The way that you define your bindings depends on your chosen programming model.

v2

The Python v2 programming model lets you define bindings using decorators directly in your Python function code. For more information, see the Python developer guide.

v1

The Python v1 programming model requires you to define bindings in a separate function.json file in the function folder. For more information, see the Python developer guide.

This article supports both programming models.

Important

The Python v2 programming model is currently in preview.
::: zone-end

Example

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

Use the queue trigger to start a function when a new item is received on a queue. The queue message is provided as input to the function.

[!INCLUDE functions-bindings-csharp-intro]

In-process

The following example shows a C# function that polls the myqueue-items queue and writes a log each time a queue item is processed.

public static class QueueFunctions
{
    [FunctionName("QueueTrigger")]
    public static void QueueTrigger(
        [QueueTrigger("myqueue-items")] string myQueueItem, 
        ILogger log)
    {
        log.LogInformation($"C# function processed: {myQueueItem}");
    }
}

Isolated process

The following example shows a C# function that polls the input-queue queue and writes several messages to an output queue each time a queue item is processed.

:::code language="csharp" source="~/azure-functions-dotnet-worker/samples/Extensions/Queue/QueueFunction.cs" id="docsnippet_queue_output_binding":::

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

The following Java example shows a storage queue trigger function, which logs the triggered message placed into queue myqueuename.

@FunctionName("queueprocessor")
public void run(
    @QueueTrigger(name = "msg",
                queueName = "myqueuename",
                connection = "myconnvarname") String message,
    final ExecutionContext context
) {
    context.getLogger().info(message);
}

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

The following example shows a queue trigger binding in a function.json file and a JavaScript function that uses the binding. The function polls the myqueue-items queue and writes a log each time a queue item is processed.

Here's the function.json file:

{
    "disabled": false,
    "bindings": [
        {
            "type": "queueTrigger",
            "direction": "in",
            "name": "myQueueItem",
            "queueName": "myqueue-items",
            "connection":"MyStorageConnectionAppSetting"
        }
    ]
}

The configuration section explains these properties.

Note

The name parameter reflects as context.bindings.<name> in the JavaScript code which contains the queue item payload. This payload is also passed as the second parameter to the function.

Here's the JavaScript code:

module.exports = async function (context, message) {
    context.log('Node.js queue trigger function processed work item', message);
    // OR access using context.bindings.<name>
    // context.log('Node.js queue trigger function processed work item', context.bindings.myQueueItem);
    context.log('expirationTime =', context.bindingData.expirationTime);
    context.log('insertionTime =', context.bindingData.insertionTime);
    context.log('nextVisibleTime =', context.bindingData.nextVisibleTime);
    context.log('id =', context.bindingData.id);
    context.log('popReceipt =', context.bindingData.popReceipt);
    context.log('dequeueCount =', context.bindingData.dequeueCount);
};

The usage section explains myQueueItem, which is named by the name property in function.json. The message metadata section explains all of the other variables shown.

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

The following example demonstrates how to read a queue message passed to a function via a trigger.

A Storage queue trigger is defined in function.json file where type is set to queueTrigger.

{
  "bindings": [
    {
      "name": "QueueItem",
      "type": "queueTrigger",
      "direction": "in",
      "queueName": "messages",
      "connection": "MyStorageConnectionAppSetting"
    }
  ]
}

The code in the Run.ps1 file declares a parameter as $QueueItem, which allows you to read the queue message in your function.

# Input bindings are passed in via param block.
param([string] $QueueItem, $TriggerMetadata)

# Write out the queue message and metadata to the information log.
Write-Host "PowerShell queue trigger function processed work item: $QueueItem"
Write-Host "Queue item expiration time: $($TriggerMetadata.ExpirationTime)"
Write-Host "Queue item insertion time: $($TriggerMetadata.InsertionTime)"
Write-Host "Queue item next visible time: $($TriggerMetadata.NextVisibleTime)"
Write-Host "ID: $($TriggerMetadata.Id)"
Write-Host "Pop receipt: $($TriggerMetadata.PopReceipt)"
Write-Host "Dequeue count: $($TriggerMetadata.DequeueCount)"

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

The following example demonstrates how to read a queue message passed to a function via a trigger. 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="QueueFunc")
@app.queue_trigger(arg_name="msg", queue_name="inputqueue",
                   connection="storageAccountConnectionString")  # Queue trigger
@app.write_queue(arg_name="outputQueueItem", queue_name="outqueue",
                 connection="storageAccountConnectionString")  # Queue output binding
def test_function(msg: func.QueueMessage,
                  outputQueueItem: func.Out[str]) -> None:
    logging.info('Python queue trigger function processed a queue item: %s',
                 msg.get_body().decode('utf-8'))
    outputQueueItem.set('hello')

v1

A Storage queue trigger is defined in function.json where type is set to queueTrigger.

{
  "scriptFile": "__init__.py",
  "bindings": [
    {
      "name": "msg",
      "type": "queueTrigger",
      "direction": "in",
      "queueName": "messages",
      "connection": "AzureStorageQueuesConnectionString"
    }
  ]
}

The code _init_.py declares a parameter as func.QueueMessage, which allows you to read the queue message in your function.

import logging
import json

import azure.functions as func

def main(msg: func.QueueMessage):
    logging.info('Python queue trigger function processed a queue item.')

    result = json.dumps({
        'id': msg.id,
        'body': msg.get_body().decode('utf-8'),
        'expiration_time': (msg.expiration_time.isoformat()
                            if msg.expiration_time else None),
        'insertion_time': (msg.insertion_time.isoformat()
                           if msg.insertion_time else None),
        'time_next_visible': (msg.time_next_visible.isoformat()
                              if msg.time_next_visible else None),
        'pop_receipt': msg.pop_receipt,
        'dequeue_count': msg.dequeue_count
    })

    logging.info(result)

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

Attributes

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

In-process

In C# class libraries, the attribute's constructor takes the name of the queue to monitor, as shown in the following example:

[FunctionName("QueueTrigger")]
public static void Run(
    [QueueTrigger("myqueue-items")] string myQueueItem, 
    ILogger log)
{
    ...
}

You can set the Connection property to specify the app setting that contains the storage account connection string to use, as shown in the following example:

[FunctionName("QueueTrigger")]
public static void Run(
    [QueueTrigger("myqueue-items", Connection = "StorageConnectionAppSetting")] string myQueueItem, 
    ILogger log)
{
    ....
}

Isolated process

In C# class libraries, the attribute's constructor takes the name of the queue to monitor, as shown in the following example:

:::code language="csharp" source="~/azure-functions-dotnet-worker/samples/Extensions/Queue/QueueFunction.cs" id="docsnippet_queue_trigger":::

This example also demonstrates setting the connection string setting in the attribute itself.

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

Annotations

The QueueTrigger annotation gives you access to the queue that triggers the function. The following example makes the queue message available to the function via the message parameter.

package com.function;
import com.microsoft.azure.functions.annotation.*;
import java.util.Queue;
import com.microsoft.azure.functions.*;

public class QueueTriggerDemo {
    @FunctionName("QueueTriggerDemo")
    public void run(
        @QueueTrigger(name = "message", queueName = "messages", connection = "MyStorageConnectionAppSetting") String message,
        final ExecutionContext context
    ) {
        context.getLogger().info("Queue message: " + message);
    }
}

Property	Description
`name`	Declares the parameter name in the function signature. When the function is triggered, this parameter's value has the contents of the queue message.
`queueName`	Declares the queue name in the storage account.
`connection`	Points to the storage account connection string.

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

Decorators

Applies only to the Python v2 programming model.

For Python v2 functions defined using decorators, the following properties on the queue_trigger decorator define the Queue Storage trigger:

Property	Description
`arg_name`	Declares the parameter name in the function signature. When the function is triggered, this parameter's value has the contents of the queue message.
`queue_name`	Declares the queue name in the storage account.
`connection`	Points to the storage account connection string.

For Python functions defined by using function.json, see the Configuration section. ::: zone-end
::: zone pivot="programming-language-javascript,programming-language-powershell,programming-language-python"

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-powershell,programming-language-python" The following table explains the binding configuration properties that you set in the function.json file and the QueueTrigger attribute.

function.json property	Description
type	Must be set to `queueTrigger`. This property is set automatically when you create the trigger in the Azure portal.
direction	In the function.json file only. Must be set to `in`. This property is set automatically when you create the trigger in the Azure portal.
name	The name of the variable that contains the queue item payload in the function code.
queueName	The name of the queue to poll.
connection	The name of an app setting or setting collection that specifies how to connect to Azure Queues. See Connections.

::: zone-end

See the Example section for complete examples.

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

Usage

Note

Functions expect a base64 encoded string. Any adjustments to the encoding type (in order to prepare data as a base64 encoded string) need to be implemented in the calling service.

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

The usage of the Queue trigger depends on the extension package version, and the C# modality used in your function app, which can be one of the following:

In-process class library

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

Isolated process

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

Choose a version to see usage details for the mode and version.

Extension 5.x+

Access the message data by using a method parameter such as string paramName. The paramName is the value specified in the QueueTriggerAttribute. You can bind to any of the following types:

Plain-old CLR object (POCO)
string
byte[]
QueueMessage

When binding to an object, the Functions runtime tries to deserialize the JSON payload into an instance of an arbitrary class defined in your code. For examples using QueueMessage, see the GitHub repository for the extension.

[!INCLUDE functions-bindings-storage-attribute]

Extension 2.x+

Access the message data by using a method parameter such as string paramName. The paramName is the value specified in the QueueTriggerAttribute. You can bind to any of the following types:

Plain-old CLR object (POCO)
string
byte[]
CloudQueueMessage

When binding to an object, the Functions runtime tries to deserialize the JSON payload into an instance of an arbitrary class defined in your code. If you try to bind to CloudQueueMessage and get an error message, make sure that you have a reference to the correct Storage SDK version.

[!INCLUDE functions-bindings-storage-attribute]

Extension 5.x+

[!INCLUDE functions-bindings-storage-queue-trigger-dotnet-isolated-types]

Extension 2.x+

Earlier versions of this extension in the isolated worker process only support binding to strings. Additional options are available to Extension 5.x+.

::: zone-end

::: zone pivot="programming-language-java" The QueueTrigger annotation gives you access to the queue message that triggered the function. ::: zone-end
::: zone pivot="programming-language-javascript"
The queue item payload is available via context.bindings.<NAME> where <NAME> matches the name defined in function.json. If the payload is JSON, the value is deserialized into an object. ::: zone-end
::: zone pivot="programming-language-powershell"
Access the queue message via string parameter that matches the name designated by binding's name parameter in the function.json file. ::: zone-end
::: zone pivot="programming-language-python"
Access the queue message via the parameter typed as QueueMessage. ::: zone-end

Metadata

The queue trigger provides several metadata properties. These properties can be used as part of binding expressions in other bindings or as parameters in your code.

::: zone pivot="programming-language-csharp" The properties are members of the CloudQueueMessage class. ::: zone-end

Property	Type	Description
`QueueTrigger`	`string`	Queue payload (if a valid string). If the queue message payload is a string, `QueueTrigger` has the same value as the variable named by the `name` property in function.json.
`DequeueCount`	`int`	The number of times this message has been dequeued.
`ExpirationTime`	`DateTimeOffset`	The time that the message expires.
`Id`	`string`	Queue message ID.
`InsertionTime`	`DateTimeOffset`	The time that the message was added to the queue.
`NextVisibleTime`	`DateTimeOffset`	The time that the message will next be visible.
`PopReceipt`	`string`	The message's pop receipt.

[!INCLUDE functions-storage-queue-connections]

Poison messages

When a queue trigger function fails, Azure Functions retries the function up to five times for a given queue message, including the first try. If all five attempts fail, the functions runtime adds a message to a queue named <originalqueuename>-poison. You can write a function to process messages from the poison queue by logging them or sending a notification that manual attention is needed.

To handle poison messages manually, check the dequeueCount of the queue message.

Peek lock

The peek-lock pattern happens automatically for queue triggers. As messages are dequeued, they are marked as invisible and associated with a timeout managed by the Storage service.

When the function starts, it starts processing a message under the following conditions.

If the function is successful, then the function execution completes and the message is deleted.
If the function fails, then the message visibility is reset. After being reset, the message is reprocessed the next time the function requests a new message.
If the function never completes due to a crash, the message visibility expires and the message re-appears in the queue.

All of the visibility mechanics are handled by the Storage service, not the Functions runtime.

Polling algorithm

The queue trigger implements a random exponential back-off algorithm to reduce the effect of idle-queue polling on storage transaction costs.

The algorithm uses the following logic:

When a message is found, the runtime waits 100 milliseconds and then checks for another message
When no message is found, it waits about 200 milliseconds before trying again.
After subsequent failed attempts to get a queue message, the wait time continues to increase until it reaches the maximum wait time, which defaults to one minute.
The maximum wait time is configurable via the maxPollingInterval property in the host.json file.

For local development the maximum polling interval defaults to two seconds.

Note

In regards to billing when hosting function apps in the Consumption plan, you are not charged for time spent polling by the runtime.

Concurrency

When there are multiple queue messages waiting, the queue trigger retrieves a batch of messages and invokes function instances concurrently to process them. By default, the batch size is 16. When the number being processed gets down to 8, the runtime gets another batch and starts processing those messages. So the maximum number of concurrent messages being processed per function on one virtual machine (VM) is 24. This limit applies separately to each queue-triggered function on each VM. If your function app scales out to multiple VMs, each VM will wait for triggers and attempt to run functions. For example, if a function app scales out to 3 VMs, the default maximum number of concurrent instances of one queue-triggered function is 72.

The batch size and the threshold for getting a new batch are configurable in the host.json file. If you want to minimize parallel execution for queue-triggered functions in a function app, you can set the batch size to 1. This setting eliminates concurrency only so long as your function app runs on a single virtual machine (VM).

The queue trigger automatically prevents a function from processing a queue message multiple times simultaneously.

host.json properties

The host.json file contains settings that control queue trigger behavior. See the host.json settings section for details regarding available settings.

Next steps

Write queue storage messages (Output binding)

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functions-bindings-storage-queue-trigger.md

functions-bindings-storage-queue-trigger.md

Azure Queue storage trigger for Azure Functions

v2

v1

Example

In-process

Isolated process

v2

v1

Attributes

In-process

Isolated process

Annotations

Decorators

Configuration

Usage

In-process class library

Isolated process

Extension 5.x+

Extension 2.x+

Extension 5.x+

Extension 2.x+

Metadata

Poison messages

Peek lock

Polling algorithm

Concurrency

host.json properties

Next steps

Files

functions-bindings-storage-queue-trigger.md

Latest commit

History

functions-bindings-storage-queue-trigger.md

File metadata and controls

Azure Queue storage trigger for Azure Functions

Example

Attributes

Annotations

Decorators

Configuration

Usage

Metadata

Poison messages

Peek lock

Polling algorithm

Concurrency

host.json properties

Next steps