Function App ServiceBusTrigger with Service Bus Emulator locally

Question

I have the service bus emulator running in a docker container. I'm able to send messages to this service bus successfully using code, but I'm unable to get function app service bus triggers to work. Specifically - I can't find the correct connection name in my config

// local.settings.json

{
  "Values": {
    "ServiceBusConnection__fullyQualifiedNamespace": "sb://localhost:5672"
  }
}

// Function1.cs

[Function(nameof(ServiceBusTest))]
public async Task ServiceBusTest(
    [ServiceBusTrigger(queueName: Queues.SmokeTest, Connection = "ServiceBusConnection")]
    RequestBase @event)
{
    await Task.CompletedTask;
}

This results in the following error

Exception: Azure.Messaging.ServiceBus.ServiceBusException: Connection refused ErrorCode: ConnectionRefused (ServiceCommunicationProblem)

I've tried a few values for my service bus connection config, but I've been getting this same error.

Here's some of the documentation for testing locally with the emulator https://learn.microsoft.com/en-us/azure/service-bus-messaging/test-locally-with-service-bus-emulator?tabs=automated-script

Jesse Squire · Accepted Answer · 2025-03-11 16:08:46Z

3

By specifying __fullqQualifiedNamespace you are directing the trigger to use Entra-based credentials for authorization with the emulator and a TLS-based connection, neither of which is supported. As a result, the emulator is refusing the connection.

To work with the emulator, you must use a connection string. Adapting your example, the updated appsettings would look like:

{
  "Values": {
    "ServiceBusConnection": "Endpoint=sb://localhost;SharedAccessKeyName=FakeKey;SharedAccessKey=FakeValue;UseDevelopmentEmulator=true;"
  }
}

The shared access key name and value are arbitrary, as they must be present but don't truly matter. The important part is ensuring the UseDevelopmentEmulator=true slug, which causes the connection to initiate without TLS for the emulator.

answered Mar 11 at 16:08

Jesse Squire

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2 Comments

tarrball Mar 12 at 16:01

This works great, but I'm struggling to find any docs that say you can do this. I don't suppose this is documented anywhere that you're aware of?

Jesse Squire Mar 12 at 17:20

@tarrball: The only emulator docs that I'm aware of is the official overview page (learn.microsoft.com/azure/service-bus-messaging/…), which really should mention this in the known limitations, but does not. I'll pass that along to the folks who own the emulator and make them aware of the confusion.

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