Disabling function with event hub trigger does not prevent binding resolution when disable setting uses underscores

[collins-benj]

Azure function app on .net 8 isolated tries to resolve a disabled function's EventHubTrigger binding. We do not have a valid event hub to connect to this listener for this environment at this time. This causes repeated The listener for function 'Functions.<FunctionName>' was unable to start. errors

Investigative information

Please provide the following:

• Timestamp: 2026-08-20T15:50:16.8188985Z
• Function App version: v4
• Invocation ID: (not available on this trace, but if it helps app id is ade49550-b1eb-46a4-b8e3-493f4163d827)
• Region: West US 2

Repro steps

Trigger like the following (using placeholders):

[Function(nameof(HandleEvents))]
public async Task HandleEvents(
    [EventHubTrigger(
        "foobar",
        Connection = "MyEH",
        IsBatched = false,
        ConsumerGroup = "MyConsumerGroup"
    )]
    EventData message
)

app settings in az portal like:

  {
    "name": "AzureWebJobs__HandleEvents__Disabled",
    "value": "true",
    "slotSetting": true
  },
  {
    "name": "MyEH__fullyQualifiedNamespace",
    "value": "default",
    "slotSetting": false
  },

note: no app slots in use in this solution.

Expected behavior

No exception thrown, no error logs

Actual behavior

Logs:

The listener for function 'Functions.HandleEvents' was unable to start.

Retrying to start listener for function 'Functions.HandleEvents' (Attempt 548)

Exception:

Microsoft.Azure.WebJobs.Host.Listeners.FunctionListenerException
at Microsoft.Azure.WebJobs.Host.Listeners.FunctionListener+d__13.MoveNext

full stacktrace:

Microsoft.Azure.WebJobs.Host.Listeners.FunctionListenerException:
System.AggregateException:
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Azure.Messaging.EventHubs.Primitives.EventProcessor`1+<StartProcessingInternalAsync>d__95.MoveNext (Azure.Messaging.EventHubs, Version=5.12.2.0, Culture=neutral, PublicKeyToken=92742159e12e44c8)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Azure.Messaging.EventHubs.Primitives.EventProcessor`1+<StartProcessingAsync>d__69.MoveNext (Azure.Messaging.EventHubs, Version=5.12.2.0, Culture=neutral, PublicKeyToken=92742159e12e44c8)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Microsoft.Azure.WebJobs.EventHubs.Processor.EventProcessorHost+<StartProcessingAsync>d__16.MoveNext (Microsoft.Azure.WebJobs.Extensions.EventHubs, Version=6.5.2.0, Culture=neutral, PublicKeyToken=014045d636e89289)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Microsoft.Azure.WebJobs.EventHubs.Listeners.EventHubListener+<StartAsync>d__17.MoveNext (Microsoft.Azure.WebJobs.Extensions.EventHubs, Version=6.5.2.0, Culture=neutral, PublicKeyToken=014045d636e89289)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Microsoft.Azure.WebJobs.Host.Listeners.FunctionListener+<StartAsync>d__13.MoveNext (Microsoft.Azure.WebJobs.Host, Version=3.0.46.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35: /_/src/Microsoft.Azure.WebJobs.Host/Listeners/FunctionListener.cs:68)
Inner exception System.Net.Sockets.SocketException handled at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw:
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Microsoft.Azure.Amqp.AsyncResult.End (Microsoft.Azure.Amqp, Version=2.7.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at Microsoft.Azure.Amqp.Transport.AmqpTransportInitiator+<>c.<ConnectAsync>b__17_1 (Microsoft.Azure.Amqp, Version=2.7.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Threading.Tasks.TaskFactory`1.FromAsyncCoreLogic (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Azure.Messaging.EventHubs.Amqp.AmqpConnectionScope+<CreateAndOpenConnectionAsync>d__81.MoveNext (Azure.Messaging.EventHubs, Version=5.12.2.0, Culture=neutral, PublicKeyToken=92742159e12e44c8)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Microsoft.Azure.Amqp.FaultTolerantAmqpObject`1+<OnCreateAsync>d__6.MoveNext (Microsoft.Azure.Amqp, Version=2.7.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Microsoft.Azure.Amqp.Singleton`1+<GetOrCreateAsync>d__24.MoveNext (Microsoft.Azure.Amqp, Version=2.7.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Microsoft.Azure.Amqp.Singleton`1+<GetOrCreateAsync>d__24.MoveNext (Microsoft.Azure.Amqp, Version=2.7.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Azure.Messaging.EventHubs.Amqp.AmqpConnectionScope+<OpenManagementLinkAsync>d__77.MoveNext (Azure.Messaging.EventHubs, Version=5.12.2.0, Culture=neutral, PublicKeyToken=92742159e12e44c8)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Azure.Messaging.EventHubs.Amqp.AmqpClient+<CreateManagementLinkAsync>d__35.MoveNext (Azure.Messaging.EventHubs, Version=5.12.2.0, Culture=neutral, PublicKeyToken=92742159e12e44c8)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Azure.Messaging.EventHubs.Amqp.AmqpClient+<CreateManagementLinkAsync>d__35.MoveNext (Azure.Messaging.EventHubs, Version=5.12.2.0, Culture=neutral, PublicKeyToken=92742159e12e44c8)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Microsoft.Azure.Amqp.FaultTolerantAmqpObject`1+<OnCreateAsync>d__6.MoveNext (Microsoft.Azure.Amqp, Version=2.7.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Microsoft.Azure.Amqp.Singleton`1+<GetOrCreateAsync>d__24.MoveNext (Microsoft.Azure.Amqp, Version=2.7.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Microsoft.Azure.Amqp.Singleton`1+<GetOrCreateAsync>d__24.MoveNext (Microsoft.Azure.Amqp, Version=2.7.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Azure.Messaging.EventHubs.Amqp.AmqpClient+<GetPropertiesAsync>d__30.MoveNext (Azure.Messaging.EventHubs, Version=5.12.2.0, Culture=neutral, PublicKeyToken=92742159e12e44c8)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Azure.Messaging.EventHubs.Amqp.AmqpClient+<GetPropertiesAsync>d__30.MoveNext (Azure.Messaging.EventHubs, Version=5.12.2.0, Culture=neutral, PublicKeyToken=92742159e12e44c8)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Azure.Messaging.EventHubs.EventHubConnection+<GetPropertiesAsync>d__37.MoveNext (Azure.Messaging.EventHubs, Version=5.12.2.0, Culture=neutral, PublicKeyToken=92742159e12e44c8)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Azure.Messaging.EventHubs.Primitives.EventProcessor`1+<ValidateEventHubsConnectionAsync>d__103.MoveNext (Azure.Messaging.EventHubs, Version=5.12.2.0, Culture=neutral, PublicKeyToken=92742159e12e44c8)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Azure.Messaging.EventHubs.Primitives.EventProcessor`1+<ValidateEventHubsConnectionAsync>d__103.MoveNext (Azure.Messaging.EventHubs, Version=5.12.2.0, Culture=neutral, PublicKeyToken=92742159e12e44c8)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Azure.Messaging.EventHubs.Primitives.EventProcessor`1+<ValidateProcessingPreconditions>d__81.MoveNext (Azure.Messaging.EventHubs, Version=5.12.2.0, Culture=neutral, PublicKeyToken=92742159e12e44c8)

Known workarounds

I could try to provide a fake event hub that actually exists but I don't want to if i don't have to.

Related information

n/a

[collins-benj]

I have found that app settings like so do NOT have this issue and have adjusted the title of this issue to match.

  {
    "name": "AzureWebJobs.HandleEvents.Disabled",
    "value": "true",
    "slotSetting": true
  }

This is very confusing to me as it seems like __ is equivalent to . in most other instances. Secondarily, using __ DOES in fact disable the function as seen in Azure Portal UX and host startup logs, it just doesn't turn off this binding resolution step.