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Queue Trigger & Bindings (.NET Core)

Watch the recording of this lesson on YouTube 🎥.

Goal 🎯

The goal of this lesson is to learn how to trigger a function by putting a message on a queue, and how you can bind an output message to a queue.

This lessons consists of the following exercises:

Nr Exercise
1 Using the Microsoft Azure Storage Explorer for Queues
2 Using string Queue output bindings
3 Using custom typed Queue output bindings
4 Using CloudQueueMessage Queue output bindings
5 Using dynamic Queue output bindings
6 Using IAsyncCollector<T> Queue output bindings
7.1 Creating a default Queue triggered function
7.2 Examine & Run the Queue triggered function
7.3 Break the Queue triggered function
7.4 Change the Queue triggered function
8 Homework
9 More info
10 Feedback

📝 Tip - If you're stuck at any point you can have a look at the source code in this repository.

📝 Tip - If you have questions or suggestions about this lesson, feel free to create a Lesson Q&A discussion here on GitHub.

1. Using the Microsoft Azure Storage Explorer for Queues

In this exercise we'll look into storage emulation and the Azure Storage Explorer to see how you can interact with queues and messages.

Steps

  1. Make sure that the storage emulator is running and open the Azure Storage Explorer.

  2. Navigate to Storage Accounts -> (Emulator - Default Ports)(Key) -> Queues Storage Emulator Treeview

  3. Right-click on Queues and select Create Queue

  4. Type a name for the queue: newplayer-items

  5. Select the new queue. Storage Emulator Queue view

    🔎 Observation - Now you see the contents of the queue. In the top menu you see actions you can perform on the queue or its items.

  6. Try adding three messages to the queue, each with different content.

  7. Now try dequeue-ing the messages.

    ❔ Question - What do you notice about the order of the messages being dequeued?

2. Using string Queue output bindings

In this exercise, we'll be creating an HttpTrigger function and use the Queue output binding with a string type in order to put player messages on the newplayer-items queue.

Steps

  1. In VSCode, create a new HTTP Trigger Function App with the following settings:

    1. Location: AzureFunctions.Queue
    2. Language: C#
    3. Template: HttpTrigger
    4. Function name: NewPlayerWithStringQueueOutput
    5. Namespace: AzureFunctionsUniversity.Demo
    6. AccessRights: Function

  2. Once the Function App is generated, add a reference to the Microsoft.Azure.WebJobs.Extensions.Storage NuGet package to the project. This allows us to use bindings for Blobs, Tables and Queues.

    📝 Tip - One way to easily do this is to use the NuGet Package Manager VSCode extension:

    1. Run NuGet Package Manager: Add new Package in the Command Palette (CTRL+SHIFT+P).
    2. Type: Microsoft.Azure.WebJobs.Extensions.Storage
    3. Select the most recent (non-preview) version of the package.

  3. We'll be working with the same Player type again as we did in the Blob lesson. Create a new file to the project, called Player.cs, and copy/paste this content into it.

  4. Now update the function method HttpTrigger argument so it looks like this:

    [HttpTrigger(
             AuthorizationLevel.Function,
             nameof(HttpMethods.Post),
             Route = null)] Player player

    🔎 Observation - The function will only allow POST requests and since we're using the Player type directly, we don't have to extract it from the request content ourselves.

    📝 Tip - When you use the HttpMethods enumeration you need to add a using to the Microsoft.AspNetCore.Http namespace.

  5. Remove the entire content of the function method and replace it with this single line:

    return JsonConvert.SerializeObject(player);

  6. Update the return type of the Run method to string, so the method declaration looks like this:

    public static string Run(...)

  7. We haven't specified how the player data will be put on the queue. First, lets add a new file, called QueueConfig.cs and copy the following into the file:

    namespace AzureFunctionsUniversity.Demo.Queue
{
   public static class QueueConfig
   {
      public const string NewPlayerItems = "newplayer-items";
   }
}

    🔎 Observation - We've now captured the name of the output queue in a string constant. We can use this constant whenever we need to refer to the name of the queue.

  8. Now let's use the newly created QueueConfig to configure what the output of our function is. Add the following underneath the FunctionName attribute (so directly above the Run method):

    [return: Queue(QueueConfig.NewPlayerItems)]

    🔎 Observation - We've just used a Queue attribute to specify this method will return a message to a queue name that is specified in QueueConfig.NewPlayerItems.

    🔎 Observation - Notice that we're not specifying the Connection property for the Blob binding. This means the storage connection of the Function App itself is used for the Blob storage. It now uses the "AzureWebJobsStorage" setting in the local.settings.json file. The value of this setting should be: "UseDevelopmentStorage=true" when emulated storage is used. When an Azure Storage Account is used this value should contain the connection string to that Storage Account.

  9. Verify that the entire function method looks as follows:

    [FunctionName(nameof(NewPlayerWithStringQueueOutput))]
[return: Queue(QueueConfig.NewPlayerItems)]
public static string Run(
    [HttpTrigger(
        AuthorizationLevel.Function,
        nameof(HttpMethods.Post),
        Route = null)] Player player)
{
    return JsonConvert.SerializeObject(player);
}

  10. Ensure that the storage emulator is started. Then build & run the AzureFunctions.Queue Function App.

    📝 Tip - When you see an error like this: Microsoft.Azure.Storage.Common: No connection could be made because the target machine actively refused it. that means that the Storage Emulator has not been started successfully and no connection can be made to it. Check the app settings in the local.settings.json and (re)start the emulated storage.

  11. Do a POST request to the function endpoint:

    POST http://localhost:7071/api/NewPlayerWithStringQueueOutput
Content-Type: application/json

{
   "id": "{{$guid}}",
   "nickName" : "Ada",
   "email" : "[email protected]",
   "region" : "United Kingdom"
}

    ❔ Question - Look at the Azure Functions console output. Is the message processed without errors?

    ❔ Question - Using the Azure Storage Explorer, check if there's a new message in the newplayer-items queue. What is the content of the message?

3. Using custom typed Queue output bindings

In this exercise, we'll be adding an HttpTrigger function and use the Queue output binding with the Player output type in order to put player messages on the newplayer-items queue.

Steps

  1. Create a copy of the NewPlayerWithStringQueueOutput.cs file and rename the file, the class and the function to NewPlayerWithTypedQueueOutput.cs.

  2. Remove the [return: Queue(QueueConfig.NewPlayerItems)] line since we won't be using the same return Queue attribute.

  3. Instead add the following Queue binding underneath the HttpTrigger:

    [Queue(QueueConfig.NewPlayerItems)] out Player playerOutput

    🔎 Observation - Here we're specifying a Queue output binding with the same queue name as before. But now we're using an out parameter of type Player. Now the return type of the function itself can be of type IActionResult, so we have more control of what kind of response we sent back to the caller of our function.

  4. Update the return type of the method to IActionResult, so the method declaration looks like this:

    public static IActionResult Run(...)

  5. Replace the contents of the function method with the following:

    IActionResult result = null;
playerOutput = null;
if (string.IsNullOrEmpty(player.Id))
{
   result = new BadRequestObjectResult("No player data in request.");
}
else
{
   playerOutput = player;
   result = new AcceptedResult();
}

return result;

    🔎 Observation - Based on the presence of a Player ID we return either a BadRequestObjectResult or an AcceptedResult. When the player object is valid it is assigned to the playerOutput object, and that object will be put on the queue.

  6. Verify that the entire function method looks as follows:

    [FunctionName(nameof(NewPlayerWithTypedQueueOutput))]
public static IActionResult Run(
    [HttpTrigger(
        AuthorizationLevel.Function,
        nameof(HttpMethods.Post),
        Route = null)] Player player,
    [Queue(QueueConfig.NewPlayerItems)] out Player playerOutput)
{
    IActionResult result = null;
    playerOutput = null;
    if (string.IsNullOrEmpty(player.Id))
    {
        result = new BadRequestObjectResult("No player data in request.");
    }
    else
    {
        playerOutput = player;
        result = new AcceptedResult();
    }

    return result;
}

  7. Build & run the AzureFunctions.Queue Function App.

  8. Do a POST request, with a complete player object, to the function endpoint:

    POST http://localhost:7071/api/NewPlayerWithTypedQueueOutput
Content-Type: application/json

{
   "id": "{{$guid}}",
   "nickName" : "Grace",
   "email" : "[email protected]",
   "region" : "United States of America"
}

    ❔ Question - > Is there a new message in the newplayer-items queue?

  9. Do a POST request, without a player ID, to the function endpoint:

    POST http://localhost:7071/api/NewPlayerWithTypedQueueOutput
Content-Type: application/json

{
   "nickName" : "Grace",
   "email" : "[email protected]",
   "region" : "United States of America"
}

    ❔ Question - > Do you receive the correct HTTP response? Is there a new message in the newplayer-items queue now?

4. Using CloudQueueMessage Queue output bindings

In this exercise, we'll be adding an HttpTrigger function and use the Queue output binding with the CloudQueueMessage output type in order to put player messages on the newplayer-items queue.

Steps

  1. Create a copy of the NewPlayerWithTypedQueueOutput.cs file and rename the file, the class and the function to NewPlayerWithCloudQueueMessageOutput.cs.

  2. We'll be using a new output type, called CloudQueueMessage. To use the latest version of this type add a reference to the Azure.Storage.Queues NuGet package to the project.

    📝 Tip - One way to easily do this is to use the NuGet Package Manager VSCode extension:

    1. Run NuGet Package Manager: Add new Package in the Command Palette (CTRL+SHIFT+P).
    2. Type: Azure.Storage.Queues
    3. Select the most recent (non-preview) version of the package.

  3. Change the output type of the Queue binding from:

    out Player playerOutput

    to

    out CloudQueueMessage message

    📝 Tip - Ensure that the CloudQueueMessage type is from the new Microsoft.Azure.Storage.Queue namespace and not the old Microsoft.WindowsAzure.Storage.Queue namespace.

  4. Now that we have defined a new output parameter named message we still need to set it with player data. Replace:

    playerOutput = null;

    with:

    message = null;

  5. A CloudQueueMessage is constructed with a byte array, or string as the message content. Let's use the string content option so serialize the Player object. Put the following code inside the else statement:

    var serializedPlayer = JsonConvert.SerializeObject(player);
message = new CloudQueueMessage(serializedPlayer);
result = new AcceptedResult();

  6. Build & run the AzureFunctions.Queue Function App.

  7. Make a POST call to the NewPlayerWithCloudQueueMessageOutput endpoint and provide a valid json body with a Player object:

    POST http://localhost:7071/api/NewPlayerWithCloudQueueMessageOutput
Content-Type: application/json

{
   "id": "{{$guid}}",
   "nickName" : "Ada",
   "email" : "[email protected]",
   "region" : "United Kingdom"
}

    ❔ Question - Inspect the newplayer-items queue. does it contain a new message?

5. Using dynamic Queue output bindings

In this exercise, we'll be adding an HttpTrigger function and use dynamic output bindings in order to put valid player messages on the newplayer-items queue, and invalid messages on a newplayer-error-items queue.

📝 Tip - Dynamic bindings are useful when output or input bindings can only be determined at runtime. In this case we'll use the dynamic binding to determine the queue name at runtime.

Steps

  1. Create a copy of the NewPlayerWithTypedQueueOutput.cs file and rename the file, the class and the function to NewPlayerWithDynamicQueueOutput.cs.

  2. Replace the line with the Queue binding attribute and parameter with:

    IBinder binder

  3. Remove the contents of the method.

  4. Now add the following sections to the method:

    1. First, initialize the result of the HTTP response and the name of the queue:

         IActionResult result;
   string queueName;

    2. Second, add an if/else statement to determine the name of the queue and the HTTP response:

         if (string.IsNullOrEmpty(player.Id))
   {
      queueName = QueueConfig.NewPlayerErrorItems;
      result = new BadRequestObjectResult("No player data in request.");
   }
   else
   {
      queueName = QueueConfig.NewPlayerItems;
      result = new AcceptedResult();
   }

    3. Then, serialize the Player object and create an instance of a CloudQueueMessage. The cloudQueueMessage will be used in the dynamic queue binding:

      var serializedPlayer = JsonConvert.SerializeObject(player);
var cloudQueueMessage = new CloudQueueMessage(serializedPlayer);

      📝 Tip - Make sure you use the CloudQueueMessage from the Microsoft.Azure.Storage.Queue namespace and not the Microsoft.WindowsAzure.Storage.Queue namespace (the latter one is outdated). A dependency to the Azure.Storage.Queues NuGet package is required for this.

    4. Finally, create a new QueueAttribute, create an instance of a CloudQueue using the binder interface and add the cloudQueueMessage to the queue as follows:

      var queueAttribute = new QueueAttribute(queueName);
var cloudQueue = await binder.BindAsync<CloudQueue>(queueAttribute);
await cloudQueue.AddMessageAsync(cloudQueueMessage);

return result;

      ❔ Question - Look into the CloudQueue type. Which other operations does this type have?

  5. Build & run the AzureFunctions.Queue Function App.

  6. First make a POST call to the NewPlayerWithDynamicQueueOutput endpoint and provide a valid json body with a Player object:

    POST http://localhost:7071/api/NewPlayerWithDynamicQueueOutput
Content-Type: application/json

{
   "id": "{{$guid}}",
   "nickName" : "Ada",
   "email" : "[email protected]",
   "region" : "United Kingdom"
}

    ❔ Question - Inspect the newplayer-items queue. Does it contain a new message?

  7. Now make a POST call to the NewPlayerWithCloudQueueMessageOutput endpoint and provide an invalid player json body as follows:

    POST http://localhost:7071/api/NewPlayerWithDynamicQueueOutput
Content-Type: application/json

{
   "nickName" : "Ada",
}

    ❔ Question - Inspect the newplayer-error-items queue. Does it contain a new message?

6. Using IAsyncCollector<T> Queue output bindings

In this exercise, we'll be adding an HttpTrigger function and use the Queue output binding with the IAsyncCollector<Player> output type in order to put multiple player messages on the newplayer-items queue when the HTTP request contains an array of Player objects.

Steps

  1. Create a copy of the NewPlayerWithTypedQueueOutput.cs file and rename the file, the class and the function to NewPlayerWithIAsyncCollectorQueueOutput.cs.

  2. Update the type of the Queue attribute and replace:

    out Player playerOutput

    with

    IAsyncCollector<Player> collector

    📝 Tip - The IAsyncCollector<T> and ICollector<T> interfaces are supported by several output bindings such as Queue, ServiceBus, and EventHubs. When this interface is used, items are added to the (in-memory) collector and not directly to the target service behind the output binding. Once the collector is flushed, either using a direct method call or automatically when the function completes, the items in the collector are transferred.

  3. Update the HTTPTrigger input type from:

    Player player

    to

    Player[] players

    🔎 Observation - Notice that we expect an array of Player items in our request.

  4. Remove the contents of the function method.

  5. Update the function method as follows: Check if there are player objects, iterate over them, add the objects to the collector, and return a AcceptedResult. If there are no players to process, return a BadRequestObjectResult:

    IActionResult result = null;
if (players.Any())
{
    foreach (var player in players)
    {
        await collector.AddAsync(player);
    }

    result = new AcceptedResult();
}
else
{
    result = new BadRequestObjectResult("No player data in request.");
}

return result;

  6. Build & run the AzureFunctions.Queue Function App.

  7. Do a POST call to the NewPlayerWithIAsyncCollectorQueueOutput endpoint and provide a valid json body with multiple Player objects:

    POST http://localhost:7071/api/NewPlayerWithIAsyncCollectorQueueOutput
Content-Type: application/json

[
   {
      "id": "{{$guid}}",
      "nickName" : "Grace",
      "email" : "[email protected]",
      "region" : "United States of America"
   },
   {
      "id": "{{$guid}}",
      "nickName" : "Ada",
      "email" : "[email protected]",
      "region" : "United Kingdom"
   },
   {
      "id": "{{$guid}}",
      "nickName" : "Margaret",
      "email" : "[email protected]",
      "region" : "United States of America"
   }
]

    ❔ Question - Have a look at the newplayer-items queue. Does it contain multiple new messages?

7.1 Creating a default Queue triggered function

In this exercise we'll create a new QueueTriggered function and trigger it with a message.

Steps

  1. Create a new Function App by running AzureFunctions: Create New Project in the VSCode Command Palette (CTRL+SHIFT+P).

    📝 Tip - Create a folder with a descriptive name since that will be used as the name for the project, e.g. AzureFunctionsUniversity.Queue.

  2. Select the language you'll be using to code the function, in this lesson we'll be using C#.

  3. Select QueueTrigger as the template.

  4. Give the function a name (e.g. HelloWorldQueueTrigger).

  5. Enter a namespace for the function (e.g. AzureFunctionsUniversity.Demo).

  6. Select Create a new local app setting.

    🔎 Observation - The local app settings file (local.settings.json) is used to store environment variables and other useful configurations.

  7. Select the Azure subscription you will be using.

  8. Since we are using the QueueTrigger, we need to provide a storage account, select one or create a new storage account.

    1. If you select a new one, provide a name (we chose azfuncstor). The name you provide must be unique to all Azure.

  9. Select a resource group or create a new one.

    1. If you create a new one, you must select a region. Use the one closest to you.

  10. Enter the name of the storage queue, you can leave the default value myqueue-items if you'd like or change it. Make sure to keep this in mind as we will be referencing it later on.

  11. When asked about storage required for debugging choose Use local emulator.

AzureFunctionsRuntime storage

Now the Function App with a Queue Trigger function will be created.

7.2 Examine & Run the Queue triggered function

Great, we've got our Function Project and Queue Trigger created, let's examine what has been generated for us.

public static class HelloWorldQueueTrigger
{
    [FunctionName("HelloWorldQueueTrigger")]
    public static void Run(
        [QueueTrigger(
            "myqueue-items",
            Connection = "azfuncstor_STORAGE")]string myQueueItem,
            ILogger log)
    {
        log.LogInformation($"C# Queue trigger function processed: {myQueueItem}");
    }
}

🔎 Observation - The QueueTrigger indicates this function will be triggered based on queue messages. The first parameter in this attribute is the name of the queue, myqueue-items. The Connection parameter contains the name of the application setting which contains the connection string. In this case a setting called azfuncstor_STORAGE should be present in the local.settings.json. If you choose to use local storage emulation instead of the Azure Storage Account you can change the value of the azfuncstor_STORAGE setting to UseDevelopmentStorage=true;

🔎 Observation - The queue message itself, named myQueueItem, is read as a string and outputted to the log inside the method.

  1. Build and run the Function App.

  2. The function will only be triggered when a message is put on the myqueue-items queue. Use the Azure Storage Explorer to add a message to this queue.

    ❔ Question - Is the function triggered once you've put a message on the queue? How can you determine this?

    📝 Tip - You can configure the behavior of the queue binding via the host.json file. Configurable settings include the frequency of polling the queue for new messages, timeout duration when processing fails, and how many messages the function will process in parallel. See the official docs for the details.

7.3. Break the Queue triggered function

Now that the queue trigger is working, let's break it! When a queue triggered function can't process the message successfully, the message will be retried a couple of time (5 times by default). When it still fails after the final retry the message will be placed on a so-called poison queue. This is a new queue dedicated for messages that can't be processed. The name of this queue is the same as the regular queue but ends with -poison.

Steps

  1. Replace the contents of the queue triggered function with this exception:

    throw new Exception("Uh oh!");

    🔎 Observation - Throwing an exception will force the function to fail processing the message. The function will retry to process the message a couple of times.

  2. Build and run the Function App. Put a breakpoint on the throw new Exception() line.

  3. Using the Azure Storage Explorer, add a message to the myqueue-items queue.

    ❔ Question - How many times is the breakpoint hit?

    ❔ Question - Once the function has stopped retrying, is there a myqueue-items-poison queue? Does it contain the message you created?

7.4. Change the Queue triggered function

Now you understand how queue triggers work, let's do something useful with the message. Let's add a Blob output binding which saves the contents of the message to a Blob container. We'll use a Player json object as the message this time.

Steps

  1. The Azure Functions project template usually references slightly outdated NuGet packages (the release cycle of these NuGet packages is shorter than that of the project template). Let's update these references so we're working with the latest bits. Update the Microsoft.Azure.WebJobs.Extensions.Storage and Microsoft.NET.Sdk.Functions NuGet packages to the most recent (non-preview) versions.

  2. Add a reference to the Azure.Storage.Blobs NuGet package to the project. Use the most recent (non-preview) version.

  3. Add the following Blob output binding to the method:

    [Blob("players", FileAccess.Write)] CloudBlobContainer blobContainer,

    📝 Tip - The CloudBlobContainer type is part of the Microsoft.Azure.Storage.Blob namespace.

  4. Add the Player.cs class, used in earlier exercises, to the project.

  5. Replace the existing body of the function method with the following:

    var player = JsonConvert.DeserializeObject<Player>(message);
var blob = blobContainer.GetBlockBlobReference($"player-{player.Id}.json");
await blob.UploadTextAsync(message);

    🔎 Observation - First the queue message will be converted to a Player object. Then a new blob reference is created where the blob name is based on the player Id. Finally the message content is uploaded to Blob Storage. Since an asynchronous method (UploadTextAsync) is used, the function method signature need to change from void to async Task. A reference to the System.Threading.Tasks namespace is required for this.

  6. The entire function method should look like this:

    [FunctionName("HelloWorldQueueTrigger")]
   public static async Task Run(
   [QueueTrigger(
      "myqueue-items",
      Connection = "azfuncstor_STORAGE")]string message,
   [Blob("players", FileAccess.Write)] CloudBlobContainer blobContainer,
   ILogger log)
{
   var player = JsonConvert.DeserializeObject<Player>(message);
   var blob = blobContainer.GetBlockBlobReference($"player-{player.Id}.json");
   await blob.UploadTextAsync(message);
}

  7. Build and run the Function App.

  8. Using the Azure Storage Explorer, add a message with the following json content to the myqueue-items queue:

    {
   "id":"2673d898-a6b4-4cef-92b0-8fc46bcf972f",
   "nickName":"Margaret",
   "email":"[email protected]",
   "region":"United States of America"
}

    ❔ Question - Is the function triggered by the message? Is a new blob available in the "players" Blob container?

8. Homework

Here is the assignment for this lesson.

9. More info

For more info about the Queue Trigger and binding have a look at the official Azure Functions Queue Storage and Bindings documentation.

10. Feedback

We love to hear from you! Was this lesson useful to you? Is anything missing? Let us know in a Feedback discussion post here on GitHub.

🔼 Lessons Index