Input and output bindings in Azure - Commands & Configuration

Introduction

Input and output bindings in Azure Functions let your function easily connect to other services without writing extra code. They help your function get data from or send data to services like storage or databases automatically.

When you want your function to automatically read messages from a queue without manual polling.

When you want to save processed data to a database without writing database connection code.

When you want to trigger your function when a new file is uploaded to cloud storage.

When you want to send output data to a service like Event Hub or Blob Storage automatically.

When you want to simplify your function code by letting Azure handle service connections.

Config File - function.json

function.json

{
  "bindings": [
    {
      "name": "myQueueItem",
      "type": "queueTrigger",
      "direction": "in",
      "queueName": "myqueue-items",
      "connection": "AzureWebJobsStorage"
    },
    {
      "name": "$return",
      "type": "blob",
      "direction": "out",
      "path": "output-container/{rand-guid}.txt",
      "connection": "AzureWebJobsStorage"
    }
  ]
}

This file defines two bindings for an Azure Function:

• Input binding: Reads messages from the queue named myqueue-items. The function triggers when a new message arrives.
• Output binding: Saves the function's return value as a blob file in output-container with a random GUID filename.
• Connection: Both bindings use the storage account connection string named AzureWebJobsStorage.

Commands

Initialize a new Azure Functions app with the .NET runtime to prepare the environment.

Terminal

func init MyFunctionApp --worker-runtime dotnet

Expected Output

Creating new Azure Functions project in C:\Users\user\MyFunctionApp

Project created successfully.

→

--worker-runtime - Specifies the language runtime for the function app.

Create a new function named QueueTriggerFunction using the queue trigger template with anonymous access.

Terminal

func new --name QueueTriggerFunction --template "Queue trigger" --authlevel anonymous

Expected Output

Created new function 'QueueTriggerFunction' using template 'Queue trigger'.

→

--name - Sets the function name.

→

--template - Specifies the trigger type template.

Start the function app locally to test the input and output bindings in action.

Terminal

func start

Expected Output

Hosting environment: Production

Content root path: C:\Users\user\MyFunctionApp

Now listening on: http://localhost:7071

Application started. Press Ctrl+C to shut down.

Send a test message to the queue to trigger the function and see the output binding save a blob.

Terminal

az storage message put --queue-name myqueue-items --content "Hello from queue" --account-name mystorageaccount

Expected Output

{"messageId":"12345","popReceipt":"abcde"}

→

--queue-name - Specifies the target queue.

→

--content - The message content to send.

Key Concept

If you remember nothing else from this pattern, remember: input and output bindings let your function automatically connect to other services without extra code.

Common Mistakes

Not specifying the correct connection string name in the binding configuration.

The function cannot connect to the service without the right connection string, causing runtime errors.

Always use the exact connection string name defined in your application settings, like AzureWebJobsStorage.

Using the wrong direction (in/out) for a binding.

The function will not trigger or output data correctly if the direction is wrong.

Set input bindings with "direction": "in" and output bindings with "direction": "out".

Forgetting to start the function app locally before testing bindings.

The function won't run and respond to triggers if the app is not running.

Always run 'func start' to launch the function app before sending test messages.

Summary

Initialize an Azure Functions app with the desired runtime.

Create a function with input and output bindings defined in function.json.

Start the function app locally to listen for triggers.

Send test data to the input service to trigger the function and produce output automatically.