Azure Functions with Azure Service Bus

Host NServiceBus endpoints with Azure Functions and Azure Service Bus triggers.

Basic usage

Endpoint configuration

NServiceBus can be registered and configured on the host builder using the UseNServiceBus extension method in the startup class:

class Startup : FunctionsStartup
{
    public override void Configure(IFunctionsHostBuilder builder)
    {
        builder.UseNServiceBus(() => new ServiceBusTriggeredEndpointConfiguration("MyFunctionsEndpoint"));
    }
}

Any services registered via the IFunctionsHostBuilder will be available to message handlers via dependency injection. The startup class must be declared via the FunctionStartup attribute: [assembly: FunctionsStartup(typeof(Startup))].

Azure Function queue trigger for NServiceBus

The Azure Function trigger for NServiceBus is auto-generated by specifying the logical endpoint name using a custom assembly attribute:

[assembly: NServiceBusEndpointName("MyFunctionsEndpoint")]

The attribute will generate the trigger function required for NServiceBus:

// <autogenerated/>
using System.Threading.Tasks;
using Microsoft.Azure.ServiceBus;
using Microsoft.Azure.WebJobs;
using Microsoft.Extensions.Logging;
using NServiceBus;

class FunctionEndpointTrigger
{
    readonly IFunctionEndpoint endpoint;

    public FunctionEndpointTrigger(IFunctionEndpoint endpoint)
    {
        this.endpoint = endpoint;
    }

    [FunctionName("NServiceBusFunctionEndpointTrigger-ASBTriggerQueue")]
    public async Task Run(
        [ServiceBusTrigger(queueName: "ASBTriggerQueue")]
        Message message,
        ILogger logger,
        ExecutionContext executionContext)
    {
        await endpoint.Process(message, executionContext, logger);
    }
}
An invalid endpoint name will generate an NSBFUNC001 error with the message Endpoint name is invalid and cannot be used to generate trigger function.

If the trigger function needs to be customized, the trigger function generation can be disabled by removing the NServiceBusEndpointName attribute. A customized trigger function can then be manually added to the project.

Overriding the trigger function name

The trigger function name is auto-generated by default. To customize the function name, the NServiceBusEndpointName attribute can be provided with an additional parameter to set the function name:

[assembly: NServiceBusEndpointName(name: "MyFunctionsEndpoint", triggerFunctionName: "MyTriggerFunction")]
An invalid trigger function name will generate an NSBFUNC002 error with the message Trigger function name is invalid and cannot be used to generate trigger function.

Dispatching outside a message handler

Triggering a message using HTTP function:

public class HttpSender
{
    readonly IFunctionEndpoint functionEndpoint;

    public HttpSender(IFunctionEndpoint functionEndpoint)
    {
        this.functionEndpoint = functionEndpoint;
    }

    [FunctionName("HttpSender")]
    public async Task<IActionResult> Run(
        [HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)] HttpRequest request, ExecutionContext executionContext, ILogger logger)
    {
        logger.LogInformation("C# HTTP trigger function received a request.");

        var sendOptions = new SendOptions();
        sendOptions.RouteToThisEndpoint();

        await functionEndpoint.Send(new TriggerMessage(), sendOptions, executionContext, logger);

        return new OkObjectResult($"{nameof(TriggerMessage)} sent.");
    }
}

Configuration

License

The license is provided via the NSERVICEBUS_LICENSE environment variable, which is set via the Function settings in the Azure Portal. For local development, use local.settings.json. In Azure, specify a Function setting using the environment variable as the key.

{
  "IsEncrypted": false,
  "Values": {
    ...
    "NSERVICEBUS_LICENSE": "<?xml version=\"1.0\" encoding=\"utf-8\"?><license id=\"1222e1d1-2222-4a46-b1c6-943c442ca710\" expiration=\"2113-11-30T00:00:00.0000000\" type=\"Standard\" LicenseType=\"Standard\" LicenseVersion=\"4.0\" MaxMessageThroughputPerSecond=\"Max\" WorkerThreads=\"Max\" AllowedNumberOfWorkerNodes=\"Max\">. . .</license>"
  }
}

Custom diagnostics

NServiceBus startup diagnostics are disabled by default when using Azure Functions. Diagnostics can be written to the logs via the following snippet:

class configureErrorQueueuOnStartup : FunctionsStartup
{
    public override void Configure(IFunctionsHostBuilder builder)
    {
        builder.UseNServiceBus(() =>
        {
            var configuration = new ServiceBusTriggeredEndpointConfiguration("MyFunctionsEndpoint");
            configuration.LogDiagnostics();
            return configuration;
        });
    }
}

Error queue

For recoverability to move the continuously failing messages to the error queue rather than to the Azure Service Bus dead-letter queue, the error queue must be created in advance and configured using the following API:

class EnableDiagnosticsOnStartup : FunctionsStartup
{
    public override void Configure(IFunctionsHostBuilder builder)
    {
        builder.UseNServiceBus(() =>
        {
            var configuration = new ServiceBusTriggeredEndpointConfiguration("MyFunctionsEndpoint");
            configuration.AdvancedConfiguration.SendFailedMessagesTo("error");
            return configuration;
        });
    }
}

Known constraints and limitations

When using Azure Functions with Azure Service Bus (ASB) the following points must be taken into consideration:

  • There is no support for the SendsAtomicWithReceive transport transaction mode.
  • The Configuration API exposes NServiceBus transport configuration options via the configuration.Transport method to allow customization; however, not all of the options will be applicable to execution within Azure Functions.

Preparing the Azure Service Bus namespace

Function endpoints cannot create their own queues or other infrastructure in the Azure Service Bus namespace.

Use the asb-transport command line (CLI) tool to provision the entities in the namespace for the Function endpoint.

Creating the endpoint queue

asb-transport endpoint create <queue name>

See the full documentation for the asb-transport endpoint create command for more details.

If the asb-tranport command-line tool is not used to create the queue, it is recommended to set the MaxDeliveryCount setting to the maximum value.

Subscribing to events

asb-transport endpoint subscribe <queue name> <eventtype>

See the full documentation for the asb-transport endpoint subscribe command for more details.

Samples


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