Azure NotificationHubClient throws SocketException when used on Azure function intensively - azure

Question

We are using an Azure function to send push notifications via Azure NotificationHubClient. This function is called a lot at peak times on live environment and as a result we got a lot of SocketExceptions thrown from the NotificationHubClient.SendNotificationAsync() method.
Exception details:
Microsoft.Azure.NotificationHubs.Messaging.MessagingException: Unexpected exception encountered TimeStamp:2020-03-27T04:14:35.4655705Z ---> System.Net.Http.HttpRequestException: Cannot assign requested address ---> System.Net.Sockets.SocketException: Cannot assign requested address
at System.Net.Http.ConnectHelper.ConnectAsync(String host, Int32 port, CancellationToken cancellationToken)
--- End of inner exception stack trace ---
at System.Net.Http.ConnectHelper.ConnectAsync(String host, Int32 port, CancellationToken cancellationToken)
at System.Threading.Tasks.ValueTask`1.get_Result()
at System.Net.Http.HttpConnectionPool.CreateConnectionAsync(HttpRequestMessage request, CancellationToken cancellationToken)
at System.Threading.Tasks.ValueTask`1.get_Result()
at System.Net.Http.HttpConnectionPool.WaitForCreatedConnectionAsync(ValueTask`1 creationTask)
at System.Threading.Tasks.ValueTask`1.get_Result()
at System.Net.Http.HttpConnectionPool.SendWithRetryAsync(HttpRequestMessage request, Boolean doRequestAuth, CancellationToken cancellationToken)
at System.Net.Http.RedirectHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
at System.Net.Http.DiagnosticsHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
at System.Net.Http.HttpClient.FinishSendAsyncBuffered(Task`1 sendTask, HttpRequestMessage request, CancellationTokenSource cts, Boolean disposeCts)
at Microsoft.Azure.NotificationHubs.NotificationHubClient.SendRequestAsync(HttpRequestMessage request, String trackingId, HttpStatusCode[] successfulResponseStatuses, CancellationToken cancellationToken)
--- End of inner exception stack trace ---
at Microsoft.Azure.NotificationHubs.ExceptionsUtility.HandleUnexpectedException(Exception ex, String trackingId)
at Microsoft.Azure.NotificationHubs.ExceptionsUtility.TranslateToMessagingException(Exception ex, Int32 timeoutInMilliseconds, String trackingId)
at Microsoft.Azure.NotificationHubs.NotificationHubClient.SendRequestAsync(HttpRequestMessage request, String trackingId, HttpStatusCode[] successfulResponseStatuses, CancellationToken cancellationToken)
at Microsoft.Azure.NotificationHubs.NotificationHubClient.SendNotificationImplAsync(Notification notification, String tagExpression, String deviceHandle, CancellationToken cancellationToken)
We create the NotificationHubClient like:
new NotificationHubClient(connectionString, hubName, new NotificationHubClientSettings
{
OperationTimeout = TimeSpan.FromSeconds(10)
});
I've observed that the Microsoft implementation behind is instantiating a new HttpClient on each new NotificationHubClient instantiation - which would probably be the problem(the well known socket exhaustion), but I have no ideea how this could be tackled.
Has anyone confronted with the same problem and managed to fix it some way? Thanks

Answer 1

In the end we managed to overcome the problem by injecting
IHttpMessageHandlerFactory _httpMessageHandlerFactory;
in our class and pass it to the notificationHubClient in the constructor:
return new NotificationHubClient(connectionString, hubName,
new NotificationHubClientSettings
{
OperationTimeout = TimeSpan.FromSeconds(10),
MessageHandler = _httpMessageHandlerFactory.CreateHandler()
});

Answer 2

There is a RESTful API for Notification Hubs. You can see it here. If you wanted more control, you could write your own wrapper around the methods you need, making sure to set the HttpClient instance as a static member variable within your Azure Function.