Azure Developers

What are Azure Functions Bindings?

Azure Functions use bindings to declaratively connect your function code to other Azure services and data sources without requiring you to write complex integration code. Bindings simplify development by allowing you to focus on your function's logic while the binding handles the input and output operations.

There are two main types of bindings:

• Input Bindings: Used to retrieve data and pass it as parameters to your function.
• Output Bindings: Used to send data from your function to another service or data store.

Bindings can also act as Triggers, which are a special type of input binding that starts your function's execution in response to an event.

Common Binding Scenarios

Let's explore some practical examples of using bindings:

1. HTTP Trigger with Output Binding to Blob Storage

Imagine a function that receives an HTTP request, processes some data, and then saves the result to Azure Blob Storage.

In your function.json (or using attributes in C#, JavaScript, etc.), you'd define an HTTP trigger and a blob output binding.

Example (Conceptual function.json):

{
  "scriptFile": "__init__.py",
  "bindings": [
    {
      "authLevel": "function",
      "type": "httpTrigger",
      "direction": "in",
      "name": "req",
      "methods": [
        "get",
        "post"
      ]
    },
    {
      "type": "http",
      "direction": "out",
      "name": "res"
    },
    {
      "name": "outputBlob",
      "type": "blob",
      "path": "myblobcontainer/{rand-guid}.txt",
      "connection": "AzureWebJobsStorage"
    }
  ]
}
                

In your code, the data bound to outputBlob can be directly written to.

2. Queue Trigger with Input Binding to Table Storage

A function triggered by a message in an Azure Queue, which then retrieves related information from Azure Table Storage before processing the message.

Example (Conceptual function.json):

{
  "scriptFile": "__init__.py",
  "bindings": [
    {
      "name": "msg",
      "type": "queueTrigger",
      "direction": "in",
      "queueName": "myqueue-items",
      "connection": "AzureWebJobsStorage"
    },
    {
      "name": "customerData",
      "type": "table",
      "direction": "in",
      "tableName": "Customers",
      "rowKey": "{CustomerId}",
      "partitionKey": "Sales",
      "connection": "AzureWebJobsStorage"
    }
  ]
}
                

The customerData parameter in your function code will be populated with the row from the "Customers" table that matches the CustomerId extracted from the queue message.

Supported Binding Types

Azure Functions supports a rich set of bindings for various Azure services and common patterns. Some popular ones include:

• Storage: Blob, Queue, Table
• Databases: Cosmos DB, SQL Server
• Messaging: Service Bus, Event Hubs, Event Grid
• Monitoring: Application Insights
• Other: Twilio, SendGrid, HTTP, Timer

You can find a comprehensive list of supported bindings in the official Azure Functions documentation.

Configuring Bindings

Bindings are configured in one of two ways, depending on your development language and project structure:

• function.json file: For Node.js, Python, and PowerShell, bindings are defined in a separate function.json file located in the same directory as your function code.
• Attributes: For .NET, Java, and TypeScript, bindings are typically defined using attributes directly within your function code, providing a more integrated experience.

Each binding configuration specifies its type, direction (in, out, or inOut), and a unique name that will be used to access the data in your function. Many bindings also require a connection string or a reference to one.