Azure Functions Documentation

Azure Functions Queue Bindings

Queue bindings enable your Azure Functions to interact with Azure Queue Storage. They provide triggers for when a new message is available in a queue and input/output bindings for reading from and writing to queues.

Trigger: Queue Trigger

A queue trigger starts your function when a new message arrives in an Azure Queue Storage queue. The message content is passed as input to your function.

Example (JavaScript):

module.exports = async function (context, myQueueItem) {
    context.log('JavaScript queue trigger function processed work item', myQueueItem);
    // Process the message content in myQueueItem
};

Example (C#):

// Assume Startup.cs configures the queue connection
// public static class QueueTriggerFunction
// {
//     [Function("QueueTriggerFunction")]
//     public static void Run(
//         [QueueTrigger("myqueue-items")] string myQueueItem,
//         FunctionContext context)
//     {
//         context.Logger.LogInformation($"C# Queue trigger function processed: {myQueueItem}");
//     }
// }

Input Binding: Queue Input

A queue input binding allows you to read a single message from a queue as input to your function. Unlike the trigger, this is typically used for polling a queue within an existing function execution.

Example (JavaScript):

module.exports = async function (context, req, myQueueItem) {
    context.log('Received queue message:', myQueueItem);
    // Use myQueueItem
    context.res = {
        body: `Processed message: ${myQueueItem}`
    };
};

Output Binding: Queue Output

A queue output binding allows your function to send a message to an Azure Queue Storage queue. You return the message content, or pass it to a context object.

Example (JavaScript):

module.exports = async function (context, req) {
    const messageToSend = req.body && req.body.message;

    if (messageToSend) {
        context.bindings.outputQueueItem = messageToSend;
        context.res = {
            status: 200,
            body: "Message sent to queue."
        };
    } else {
        context.res = {
            status: 400,
            body: "Please provide a message to send."
        };
    }
};

Example (C#):

// public static class QueueOutputFunction
// {
//     [Function("QueueOutputFunction")]
//     [QueueOutput("output-queue")]
//     public static string Run(
//         [HttpTrigger(AuthorizationLevel.Function, "post")] HttpRequest req,
//         FunctionContext context)
//     {
//         string message = req.ReadAsStringAsync().Result;
//         context.Logger.LogInformation($"Sending message to output queue: {message}");
//         return message;
//     }
// }

Configuration

Queue bindings require configuration to connect to your Azure Storage account. This is typically done in the function.json file (for non-language specific configuration) or through attributes in your code (e.g., C#).

function.json Example (Trigger):

{
  "scriptFile": "index.js",
  "bindings": [
    {
      "name": "myQueueItem",
      "type": "queueTrigger",
      "direction": "in",
      "queueName": "myqueue-items",
      "connection": "AzureWebJobsStorage"
    }
  ]
}

function.json Example (Output):

{
  "scriptFile": "index.js",
  "bindings": [
    {
      "name": "outputQueueItem",
      "type": "queue",
      "direction": "out",
      "queueName": "output-queue",
      "connection": "AzureWebJobsStorage"
    }
  ]
}

The connection property refers to a setting in your Azure Functions application settings, typically named AzureWebJobsStorage, which holds your Azure Storage connection string.

Key Properties

Best Practices

• Use clear and descriptive queueName values.
• Ensure your storage connection string is securely managed in application settings.
• Handle potential errors and poison messages appropriately.
• Consider message idempotency for queue triggers to prevent duplicate processing.