Azure Function ServiceBusTrigger triggers multiple times the same message within milliseconds without the first finishing

Question

Why does the serviceBus triggers the same message multiple times? The same triggers get executed by the same message on the service bus:

[FunctionName("ProcessOrderFromServiceBusQueue")]
        public static void RunQueueMessages(
            [ServiceBusTrigger("orderqueue", Connection = "ServiceBusConnectionString")]
            string myQueueItem,
            int deliveryCount,
            DateTime enqueuedTimeUtc,
            string messageId,
            long sequenceNumber,
            TraceWriter log, ExecutionContext context)
        {
            log.Info($"C# ServiceBus Queue trigger function processed message: {myQueueItem}");            

            var config = new ConfigurationBuilder()
                                .SetBasePath(context.FunctionAppDirectory)
                                .AddJsonFile("local.settings.json", optional: true, reloadOnChange: true)
                                .AddEnvironmentVariables()
                                .Build();

            //var conn = config["ServiceBusConnectionString"];
            //var queueName = config["QueueName"];
            //var queueClient = new QueueClient(conn, queueName);
            //queueClient.CompleteAsync()
            log.Info($"Received Order: OrderId:{messageId} SequenceNumber:{sequenceNumber} Body:{myQueueItem}");


            // Deserialize the message body
            var order = JsonConvert.DeserializeObject<Order>(myQueueItem);

            // Process the order
            ProcessOrder(order, log, config);

            log.Info($"C# ServiceBus queue trigger function processed message: {messageId}");
        }

Answer 1

Most probably the body of your function throws exception during message processing. Function App aborts its processing, the message returns to the queue and immediately gets dispatched again, just to fail again and so on.

In the end, it hits Max Delivery Count and is parked in Dead Letter queue.

Could you check my hypothesis? E.g. print deliveryCount too, and check what's in DLQ.