Azure Service Bus trigger for Azure Functions

Use the Service Bus trigger to respond to messages from a Service Bus queue or topic. Starting with extension version 3.1.0, you can trigger on a session-enabled queue or topic.

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

Example

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

  • In-process class library: compiled C# function that runs in the same process as the Functions runtime.
  • Isolated process class library: compiled C# function that runs in a process isolated from the runtime. Isolated process is required to support C# functions running on .NET 5.0.
  • C# script: used primarily when creating C# functions in the Azure portal.

The following example shows a C# function that reads message metadata and logs a Service Bus queue message:

[FunctionName("ServiceBusQueueTriggerCSharp")]                    
public static void Run(
    [ServiceBusTrigger("myqueue", Connection = "ServiceBusConnection")] 
    string myQueueItem,
    Int32 deliveryCount,
    DateTime enqueuedTimeUtc,
    string messageId,
    ILogger log)
{
    log.LogInformation($"C# ServiceBus queue trigger function processed message: {myQueueItem}");
    log.LogInformation($"EnqueuedTimeUtc={enqueuedTimeUtc}");
    log.LogInformation($"DeliveryCount={deliveryCount}");
    log.LogInformation($"MessageId={messageId}");
}

The following Java function uses the @ServiceBusQueueTrigger annotation from the Java functions runtime library to describe the configuration for a Service Bus queue trigger. The function grabs the message placed on the queue and adds it to the logs.

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

Java functions can also be triggered when a message is added to a Service Bus topic. The following example uses the @ServiceBusTopicTrigger annotation to describe the trigger configuration.

@FunctionName("sbtopicprocessor")
    public void run(
        @ServiceBusTopicTrigger(
            name = "message",
            topicName = "mytopicname",
            subscriptionName = "mysubscription",
            connection = "ServiceBusConnection"
        ) String message,
        final ExecutionContext context
    ) {
        context.getLogger().info(message);
    }

The following example shows a Service Bus trigger binding in a function.json file and a JavaScript function that uses the binding. The function reads message metadata and logs a Service Bus queue message.

Here's the binding data in the function.json file:

{
"bindings": [
    {
    "queueName": "testqueue",
    "connection": "MyServiceBusConnection",
    "name": "myQueueItem",
    "type": "serviceBusTrigger",
    "direction": "in"
    }
],
"disabled": false
}

Here's the JavaScript script code:

module.exports = async function(context, myQueueItem) {
    context.log('Node.js ServiceBus queue trigger function processed message', myQueueItem);
    context.log('EnqueuedTimeUtc =', context.bindingData.enqueuedTimeUtc);
    context.log('DeliveryCount =', context.bindingData.deliveryCount);
    context.log('MessageId =', context.bindingData.messageId);
};

The following example shows a Service Bus trigger binding in a function.json file and a PowerShell function that uses the binding.

Here's the binding data in the function.json file:

{
  "bindings": [
    {
      "name": "mySbMsg",
      "type": "serviceBusTrigger",
      "direction": "in",
      "topicName": "mytopic",
      "subscriptionName": "mysubscription",
      "connection": "AzureServiceBusConnectionString"
    }
  ]
}

Here's the function that runs when a Service Bus message is sent.

param([string] $mySbMsg, $TriggerMetadata)

Write-Host "PowerShell ServiceBus queue trigger function processed message: $mySbMsg"

The following example demonstrates how to read a Service Bus queue message via a trigger.

A Service Bus binding is defined in function.json where type is set to serviceBusTrigger.

{
  "scriptFile": "__init__.py",
  "bindings": [
    {
      "name": "msg",
      "type": "serviceBusTrigger",
      "direction": "in",
      "queueName": "inputqueue",
      "connection": "AzureServiceBusConnectionString"
    }
  ]
}

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

import azure.functions as func

import logging
import json

def main(msg: func.ServiceBusMessage):
    logging.info('Python ServiceBus queue trigger processed message.')

    result = json.dumps({
        'message_id': msg.message_id,
        'body': msg.get_body().decode('utf-8'),
        'content_type': msg.content_type,
        'expiration_time': msg.expiration_time,
        'label': msg.label,
        'partition_key': msg.partition_key,
        'reply_to': msg.reply_to,
        'reply_to_session_id': msg.reply_to_session_id,
        'scheduled_enqueue_time': msg.scheduled_enqueue_time,
        'session_id': msg.session_id,
        'time_to_live': msg.time_to_live,
        'to': msg.to,
        'user_properties': msg.user_properties,
        'metadata' : msg.metadata
    }, default=str)

    logging.info(result)

Attributes

Both in-process and isolated process C# libraries use the ServiceBusTriggerAttribute attribute to define the function trigger. C# script instead uses a function.json configuration file.

The following table explains the properties you can set using this trigger attribute:

Property Description
QueueName Name of the queue to monitor. Set only if monitoring a queue, not for a topic.
TopicName Name of the topic to monitor. Set only if monitoring a topic, not for a queue.
SubscriptionName Name of the subscription to monitor. Set only if monitoring a topic, not for a queue.
Connection The name of an app setting or setting collection that specifies how to connect to Service Bus. See Connections.
Access Access rights for the connection string. Available values are manage and listen. The default is manage, which indicates that the connection has the Manage permission. If you use a connection string that does not have the Manage permission, set accessRights to "listen". Otherwise, the Functions runtime might fail trying to do operations that require manage rights. In Azure Functions version 2.x and higher, this property is not available because the latest version of the Service Bus SDK doesn't support manage operations.
IsBatched Messages are delivered in batches. Requires an array or collection type.
IsSessionsEnabled true if connecting to a session-aware queue or subscription. false otherwise, which is the default value.
AutoComplete true Whether the trigger should automatically call complete after processing, or if the function code will manually call complete.

If set to true, the trigger completes the message automatically if the function execution completes successfully, and abandons the message otherwise.

When set to false, you are responsible for calling MessageReceiver methods to complete, abandon, or deadletter the message. If an exception is thrown (and none of the MessageReceiver methods are called), then the lock remains. Once the lock expires, the message is re-queued with the DeliveryCount incremented and the lock is automatically renewed.

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

Annotations

The ServiceBusQueueTrigger annotation allows you to create a function that runs when a Service Bus queue message is created. Configuration options available include the following properties:

Property Description
name The name of the variable that represents the queue or topic message in function code.
queueName Name of the queue to monitor. Set only if monitoring a queue, not for a topic.
topicName Name of the topic to monitor. Set only if monitoring a topic, not for a queue.
subscriptionName Name of the subscription to monitor. Set only if monitoring a topic, not for a queue.
connection The name of an app setting or setting collection that specifies how to connect to Service Bus. See Connections.

The ServiceBusTopicTrigger annotation allows you to designate a topic and subscription to target what data triggers the function.

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

See the trigger example for more detail.

Configuration

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

function.json property Description
type Must be set to serviceBusTrigger. This property is set automatically when you create the trigger in the Azure portal.
direction 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 represents the queue or topic message in function code.
queueName Name of the queue to monitor. Set only if monitoring a queue, not for a topic.
topicName Name of the topic to monitor. Set only if monitoring a topic, not for a queue.
subscriptionName Name of the subscription to monitor. Set only if monitoring a topic, not for a queue.
connection The name of an app setting or setting collection that specifies how to connect to Service Bus. See Connections.
accessRights Access rights for the connection string. Available values are manage and listen. The default is manage, which indicates that the connection has the Manage permission. If you use a connection string that does not have the Manage permission, set accessRights to "listen". Otherwise, the Functions runtime might fail trying to do operations that require manage rights. In Azure Functions version 2.x and higher, this property is not available because the latest version of the Service Bus SDK doesn't support manage operations.
isSessionsEnabled true if connecting to a session-aware queue or subscription. false otherwise, which is the default value.
autoComplete Must be true for non-C# functions, which means that the trigger should either automatically call complete after processing, or the function code manually calls complete.

When set to true, the trigger completes the message automatically if the function execution completes successfully, and abandons the message otherwise.

Exceptions in the function results in the runtime calls abandonAsync in the background. If no exception occurs, then completeAsync is called in the background. This property is available only in Azure Functions 2.x and higher.

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

See the Example section for complete examples.

Usage

The following parameter types are supported by all C# modalities and extension versions:

Type Description
System.String Use when the message is simple text.
byte[] Use for binary data messages.
Object When a message contains JSON, Functions tries to deserialize the JSON data into known plain-old CLR object type.

Messaging-specific parameter types contain additional message metadata. The specific types supported by the Service Bus trigger depend on the Functions runtime version, the extension package version, and the C# modality used.

Use the ServiceBusReceivedMessage type to receive message metadata from Service Bus Queues and Subscriptions. To learn more, see Messages, payloads, and serialization.

In C# class libraries, the attribute's constructor takes the name of the queue or the topic and subscription.

You can also use the ServiceBusAccountAttribute to specify the Service Bus account to use. The constructor takes the name of an app setting that contains a Service Bus connection string. The attribute can be applied at the parameter, method, or class level. The following example shows class level and method level:

[ServiceBusAccount("ClassLevelServiceBusAppSetting")]
public static class AzureFunctions
{
    [ServiceBusAccount("MethodLevelServiceBusAppSetting")]
    [FunctionName("ServiceBusQueueTriggerCSharp")]
    public static void Run(
        [ServiceBusTrigger("myqueue", AccessRights.Manage)] 
        string myQueueItem, ILogger log)
{
    ...
}

The Service Bus account to use is determined in the following order:

  • The ServiceBusTrigger attribute's Connection property.
  • The ServiceBusAccount attribute applied to the same parameter as the ServiceBusTrigger attribute.
  • The ServiceBusAccount attribute applied to the function.
  • The ServiceBusAccount attribute applied to the class.
  • The AzureWebJobsServiceBus app setting.

When the Connection property isn't defined, Functions looks for an app setting named AzureWebJobsServiceBus, which is the default name for the Service Bus connection string. You can also set the Connection property to specify the name of an application setting that contains the Service Bus connection string to use.

The incoming Service Bus message is available via a ServiceBusQueueMessage or ServiceBusTopicMessage parameter.

Access the queue or topic message by using context.bindings.<name from function.json>. The Service Bus message is passed into the function as either a string or JSON object.

The Service Bus instance is available via the parameter configured in the function.json file's name property.

The queue message is available to the function via a parameter typed as func.ServiceBusMessage. The Service Bus message is passed into the function as either a string or JSON object.

For a complete example, see the examples section.

Connections

The connection property is a reference to environment configuration which specifies how the app should connect to Service Bus. It may specify:

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.

Connection string

To obtain a connection string, follow the steps shown at Get the management credentials. The connection string must be for a Service Bus namespace, not limited to a specific queue or topic.

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. For example, if you set connection to "MyServiceBus", the Functions runtime looks for an app setting that is named "AzureWebJobsMyServiceBus". If you leave connection empty, the Functions runtime uses the default Service Bus connection string in the app setting that is named "AzureWebJobsServiceBus".

Identity-based connections

If you are using version 5.x or higher of the extension, instead of using a connection string with a secret, you can have the app use an Azure Active Directory identity. To do this, you would define settings under a common prefix which maps to the connection property in the trigger and binding configuration.

In this mode, the extension requires the following properties:

Property Environment variable template Description Example value
Fully Qualified Namespace <CONNECTION_NAME_PREFIX>__fullyQualifiedNamespace The fully qualified Service Bus namespace. <service_bus_namespace>.servicebus.windows.net

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

Note

When using Azure App Configuration or Key Vault to provide settings for Managed Identity connections, setting names should use a valid key separator such as : or / in place of the __ to ensure names are resolved correctly.

For example, <CONNECTION_NAME_PREFIX>:fullyQualifiedNamespace.

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.

Grant permission to the identity

Whatever identity is being used must have permissions to perform the intended actions. You will 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'll need to create a role assignment that provides access to your topics and queues at runtime. Management roles like Owner aren't sufficient. The following table shows built-in roles that are recommended when using the Service Bus extension in normal operation. Your application may require additional permissions based on the code you write.

Binding type Example built-in roles
Trigger1 Azure Service Bus Data Receiver, Azure Service Bus Data Owner
Output binding Azure Service Bus Data Sender

1 For triggering from Service Bus topics, the role assignment needs to have effective scope over the Service Bus subscription resource. If only the topic is included, an error will occur. Some clients, such as the Azure portal, don't expose the Service Bus subscription resource as a scope for role assignment. In such cases, the Azure CLI may be used instead. To learn more, see Azure built-in roles for Azure Service Bus.

Poison messages

Poison message handling can't be controlled or configured in Azure Functions. Service Bus handles poison messages itself.

PeekLock behavior

The Functions runtime receives a message in PeekLock mode. It calls Complete on the message if the function finishes successfully, or calls Abandon if the function fails. If the function runs longer than the PeekLock timeout, the lock is automatically renewed as long as the function is running.

The maxAutoRenewDuration is configurable in host.json, which maps to OnMessageOptions.MaxAutoRenewDuration. The default value of this setting is 5 minutes.

Message metadata

Messaging-specific types let you easily retrieve metadata as properties of the object. These properties depend on the Functions runtime version, the extension package version, and the C# modality used.

These properties are members of the ServiceBusReceivedMessage class.

Property Type Description
ApplicationProperties ApplicationProperties Properties set by the sender.
ContentType string A content type identifier utilized by the sender and receiver for application-specific logic.
CorrelationId string The correlation ID.
DeliveryCount Int32 The number of deliveries.
EnqueuedTime DateTime The enqueued time in UTC.
ScheduledEnqueueTimeUtc DateTime The scheduled enqueued time in UTC.
ExpiresAt DateTime The expiration time in UTC.
MessageId string A user-defined value that Service Bus can use to identify duplicate messages, if enabled.
ReplyTo string The reply to queue address.
Subject string The application-specific label which can be used in place of the Label metadata property.
To string The send to address.

Next steps