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Showing content from https://learn.microsoft.com/en-us/azure/azure-functions/functions-bindings-storage-queue-trigger below:

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.

Important

This article uses tabs to support multiple versions of the Node.js programming model. The v4 model is generally available and is designed to have a more flexible and intuitive experience for JavaScript and TypeScript developers. For more details about how the v4 model works, refer to the Azure Functions Node.js developer guide. To learn more about the differences between v3 and v4, refer to the migration guide.

Azure Functions supports two programming models for Python. The way that you define your bindings depends on your chosen programming model.

• v2
• v1

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.

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.

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.

A C# function can be created by using one of the following C# modes:

• Isolated worker model: Compiled C# function that runs in a worker process that's isolated from the runtime. Isolated worker process is required to support C# functions running on LTS and non-LTS versions .NET and the .NET Framework. Extensions for isolated worker process functions use Microsoft.Azure.Functions.Worker.Extensions.* namespaces.
• In-process model: Compiled C# function that runs in the same process as the Functions runtime. In a variation of this model, Functions can be run using C# scripting, which is supported primarily for C# portal editing. Extensions for in-process functions use Microsoft.Azure.WebJobs.Extensions.* namespaces.

• Isolated worker model
• In-process model

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.

[Function(nameof(QueueFunction))]
[QueueOutput("output-queue")]
public string[] Run([QueueTrigger("input-queue")] Album myQueueItem, FunctionContext context)
{
    // Use a string array to return more than one message.
    string[] messages = {
        $"Album name = {myQueueItem.Name}",
        $"Album songs = {myQueueItem.Songs}"};

    _logger.LogInformation("{msg1},{msg2}", messages[0], messages[1]);

    // Queue Output messages
    return messages;
}

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}");
    }
}

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);
}

• Model v4
• Model v3

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

import { app, InvocationContext } from '@azure/functions';

export async function storageQueueTrigger1(queueItem: unknown, context: InvocationContext): Promise<void> {
    context.log('Storage queue function processed work item:', queueItem);
    context.log('expirationTime =', context.triggerMetadata.expirationTime);
    context.log('insertionTime =', context.triggerMetadata.insertionTime);
    context.log('nextVisibleTime =', context.triggerMetadata.nextVisibleTime);
    context.log('id =', context.triggerMetadata.id);
    context.log('popReceipt =', context.triggerMetadata.popReceipt);
    context.log('dequeueCount =', context.triggerMetadata.dequeueCount);
}

app.storageQueue('storageQueueTrigger1', {
    queueName: 'myqueue-items',
    connection: 'MyStorageConnectionAppSetting',
    handler: storageQueueTrigger1,
});

The usage section explains queueItem. The message metadata section explains all of the other variables shown.

TypeScript samples aren't documented for model v3.

• Model v4
• Model v3

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

const { app } = require('@azure/functions');

app.storageQueue('storageQueueTrigger1', {
    queueName: 'myqueue-items',
    connection: 'MyStorageConnectionAppSetting',
    handler: (queueItem, context) => {
        context.log('Storage queue function processed work item:', queueItem);
        context.log('expirationTime =', context.triggerMetadata.expirationTime);
        context.log('insertionTime =', context.triggerMetadata.insertionTime);
        context.log('nextVisibleTime =', context.triggerMetadata.nextVisibleTime);
        context.log('id =', context.triggerMetadata.id);
        context.log('popReceipt =', context.triggerMetadata.popReceipt);
        context.log('dequeueCount =', context.triggerMetadata.dequeueCount);
    },
});

The usage section explains queueItem. The message metadata section explains all of the other variables shown.

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.

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)"

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
• v1

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.queue_output(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')

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)

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.

• Isolated worker model
• In-process model

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

[Function(nameof(QueueFunction))]
[QueueOutput("output-queue")]
public string[] Run([QueueTrigger("input-queue")] Album myQueueItem, FunctionContext context)

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

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)
{
    ....
}

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);
    }
}

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:

For Python functions defined by using function.json, see the Configuration section.

Applies only to the Python v1 programming model.

• Model v4
• Model v3

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

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

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

See the Example section for complete examples.

When you're developing locally, add your application settings in the local.settings.json file in the Values collection.

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.

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 these modes:

• Isolated worker model
• In-process class library

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

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

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

• Extension 5.x+
• Extension 2.x+
• Extension 5.x+
• 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 .NET 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.

While the attribute takes a Connection property, you can also use the StorageAccountAttribute to specify a storage account connection. You can do this when you need to use a different storage account than other functions in the library. The constructor takes the name of an app setting that contains a storage connection string. The attribute can be applied at the parameter, method, or class level. The following example shows class level and method level:

[StorageAccount("ClassLevelStorageAppSetting")]
public static class AzureFunctions
{
    [FunctionName("StorageTrigger")]
    [StorageAccount("FunctionLevelStorageAppSetting")]
    public static void Run( //...
{
    ...
}

The storage account to use is determined in the following order:

• The trigger or binding attribute's Connection property.
• The StorageAccount attribute applied to the same parameter as the trigger or binding attribute.
• The StorageAccount attribute applied to the function.
• The StorageAccount attribute applied to the class.
• The default storage account for the function app, which is defined in the AzureWebJobsStorage application setting.

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.

While the attribute takes a Connection property, you can also use the StorageAccountAttribute to specify a storage account connection. You can do this when you need to use a different storage account than other functions in the library. The constructor takes the name of an app setting that contains a storage connection string. The attribute can be applied at the parameter, method, or class level. The following example shows class level and method level:

[StorageAccount("ClassLevelStorageAppSetting")]
public static class AzureFunctions
{
    [FunctionName("StorageTrigger")]
    [StorageAccount("FunctionLevelStorageAppSetting")]
    public static void Run( //...
{
    ...
}

The storage account to use is determined in the following order:

• The trigger or binding attribute's Connection property.
• The StorageAccount attribute applied to the same parameter as the trigger or binding attribute.
• The StorageAccount attribute applied to the function.
• The StorageAccount attribute applied to the class.
• The default storage account for the function app, which is defined in the AzureWebJobsStorage application setting.

The queue trigger can bind to the following types:

¹ To use these types, you need to reference Microsoft.Azure.Functions.Worker.Extensions.Storage.Queues 5.2.0 or later and the common dependencies for SDK type bindings.

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

The QueueTrigger annotation gives you access to the queue message that triggered the function.

• Model v4
• Model v3

Access the queue item as the first argument to your function. If the payload is JSON, the value is deserialized into an object.

Access the queue item using context.bindings.<NAME> where <NAME> matches the value defined in function.json. If the payload is JSON, the value is deserialized into an object.

Access the queue message via string parameter that matches the name designated by binding's name parameter in the function.json file.

Access the queue message via the parameter typed as QueueMessage.

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, for language workers that provide this access to message metadata.

The message metadata properties are members of the CloudQueueMessage class.

The message metadata properties can be accessed from context.triggerMetadata.

The message metadata properties can be accessed from the passed $TriggerMetadata parameter.

The following message metadata properties can be accessed from the passed binding parameter (msg in previous examples).

The connection property is a reference to environment configuration that specifies how the app should connect to Azure Queues. It may specify:

• The name of an application setting containing a connection string
• The name of a shared prefix for multiple application settings, together defining an identity-based connection.

If the configured value is both an exact match for a single setting and a prefix match for other settings, the exact match is used.

To obtain a connection string, follow the steps shown at Manage storage account access keys.

This connection string should be stored in an application setting with a name matching the value specified by the connection property of the binding configuration.

If the app setting name begins with "AzureWebJobs", you can specify only the remainder of the name here. For example, if you set connection to "MyStorage", the Functions runtime looks for an app setting that is named "AzureWebJobsMyStorage." If you leave connection empty, the Functions runtime uses the default Storage connection string in the app setting that is named AzureWebJobsStorage.

If you're using version 5.x or higher of the extension (bundle 3.x or higher for non-.NET language stacks), instead of using a connection string with a secret, you can have the app use an Microsoft Entra identity. To use an identity, you define settings under a common prefix that maps to the connection property in the trigger and binding configuration.

If you're setting connection to "AzureWebJobsStorage", see Connecting to host storage with an identity. For all other connections, the extension requires the following properties:

¹ <CONNECTION_NAME_PREFIX>__serviceUri can be used as an alias. If both forms are provided, the queueServiceUri form is used. The serviceUri form can't be used when the overall connection configuration is to be used across blobs, queues, and/or tables.

Other properties may be set to customize the connection. See Common properties for identity-based connections.

When hosted in the Azure Functions service, identity-based connections use a managed identity. The system-assigned identity is used by default, although a user-assigned identity can be specified with the credential and clientID properties. Note that configuring a user-assigned identity with a resource ID is not supported. When run in other contexts, such as local development, your developer identity is used instead, although this can be customized. See Local development with identity-based connections.

Whatever identity is being used must have permissions to perform the intended actions. For most Azure services, this means you need to assign a role in Azure RBAC, using either built-in or custom roles which provide those permissions.

Important

Some permissions might be exposed by the target service that are not necessary for all contexts. Where possible, adhere to the principle of least privilege, granting the identity only required privileges. For example, if the app only needs to be able to read from a data source, use a role that only has permission to read. It would be inappropriate to assign a role that also allows writing to that service, as this would be excessive permission for a read operation. Similarly, you would want to ensure the role assignment is scoped only over the resources that need to be read.

You will need to create a role assignment that provides access to your queue at runtime. Management roles like Owner are not sufficient. The following table shows built-in roles that are recommended when using the Queue Storage extension in normal operation. Your application may require additional permissions based on the code you write.

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.

The peek-lock pattern happens automatically for queue triggers, using the visibility mechanics provided by the storage service. As messages are dequeued by the triggered function, they're marked as invisible. Execution of a queue triggered function can have one of these results on message in the queue:

• Function execution completes successfully and the message is deleted from the queue.
• Function execution fails and the Functions host updates the visibility of the message based on the visibilityTimeout setting in the host.json file. The default visibility timeout is zero, which means that the message immediately reappears in the queue for reprocessing. Use the visibilityTimeout setting to delay the reprocessing of messages that fail to process. This timeout setting applies to all queue triggered functions in the function app.
• The Functions host crashes during function execution. When this uncommon event occurs, the host can't apply the visibilityTimeout to the message being processed. Instead, the message is left with the default 10 minute timeout set by the storage service. After 10 minutes, the message reappears in the queue for reprocessing. This service-defined default timeout can't be changed.

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.

During 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.

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 waits 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.

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

• Write queue storage messages (Output binding)

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