The QueueTrigger function retry “rabbit hole”

My first couple of attempts at an Azure Queue Trigger Function which could do retries when an uplink message couldn’t be processed immediately(I didn’t want to throw an exception as this was just a transient issue) didn’t work. I wanted to return the uplink message to the Azure Storage Queue with the initial visibility set to a couple of seconds without throwing an exception.

I tried decorating the method with an Azure Storage Queue output binding but finally settled on the approach below. I can insert a single message into the storage queue and the application would start looping every minute.

public static class UplinkMessageProcessor
{
   const string RunTag = "Processor001";
   static int ConcurrentThreadCount = 0;
   static int MessagesProcessed = 0;

   [FunctionName("UplinkMessageProcessor")]
   public static void Run(
      [QueueTrigger("%UplinkQueueName%", Connection = "AzureStorageConnectionString")] 
      CloudQueueMessage cloudQueueMessage, 
      IBinder binder, ILogger log)
   {
      try
      {
         Interlocked.Increment(ref ConcurrentThreadCount);
         Interlocked.Increment(ref MessagesProcessed);

         log.LogInformation($"{MessagesProcessed} {RunTag} Threads:{ConcurrentThreadCount}");

         CloudQueue outputQueue = binder.Bind<CloudQueue>(new QueueAttribute("%UplinkQueueName%"));

         CloudQueueMessage message = new CloudQueueMessage(cloudQueueMessage.AsString);

         outputQueue.AddMessage(message, initialVisibilityDelay: new TimeSpan(0, 1, 0));
    
         Thread.Sleep(2000);

         Interlocked.Decrement(ref ConcurrentThreadCount);
      }
      catch (Exception ex)
      {
         log.LogError(ex, "Processing of Uplink message failed");

         throw;
      }
   }
}

I used the binder.bind method to get the CloudQueue and CloudQueueMessage details so I could insert a hidden messages back into the queue.

The version of Azure Storage queue libraries used by the function bindings (Sep 2020) may cause some compile time warnings if you select the wrong NuGet package.

Hopefully this has enough keywords that someone trying todo the same thing finds it.

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