Azure Functions

Azure Functions API Concepts

Azure Functions provides a powerful, serverless compute service that enables you to run small pieces of code, or "functions," in the cloud without explicitly provisioning or managing infrastructure. This document explores the core API concepts that underpin how you interact with and build Azure Functions.

Core Concepts

Understanding these fundamental concepts is key to effectively developing and deploying Azure Functions:

• Function Triggers: The event that causes a function to execute. Triggers are inbound and receive data that is then passed to the function.
• Bindings: Declarative ways to connect functions to other Azure services or external data sources without writing new integration code. Bindings can be used for both input and output.
• Function Runtime: The environment in which your functions execute. This includes the host process and the language worker.
• Function Host: The process that hosts your functions and manages their lifecycle, including trigger processing and execution.
• Input and Output: How data flows into and out of your functions, often facilitated by bindings.

Triggers

Triggers are the entry points for your functions. They define the specific event that will cause your function to run. Common triggers include:

• HTTP Trigger: Executes your function when an HTTP request is received. Ideal for building web APIs and microservices.
• Timer Trigger: Executes your function on a schedule (e.g., every 5 minutes, daily at midnight).
• Blob Trigger: Executes your function when a blob is added, updated, or deleted in Azure Blob Storage.
• Queue Trigger: Executes your function in response to a message appearing in an Azure Storage Queue.
• Cosmos DB Trigger: Executes your function when changes occur in a Cosmos DB collection.

{
  "scriptFile": "index.js",
  "entryPoint": "run",
  "bindings": [
    {
      "authLevel": "function",
      "type": "httpTrigger",
      "direction": "in",
      "name": "req",
      "methods": [
        "get",
        "post"
      ]
    },
    {
      "type": "http",
      "direction": "out",
      "name": "res"
    }
  ]
}
                    

Bindings

Bindings simplify data access by abstracting away the complexities of SDKs and client libraries. They allow you to declare inputs and outputs in your function's configuration.

• Input Bindings: Provide data to your function from an external service.
• Output Bindings: Send data from your function to an external service.

For example, you can use an Azure Table Storage input binding to retrieve a row based on a key passed in the trigger, or an Azure Service Bus output binding to send a message to a queue.

{
  "scriptFile": "index.js",
  "entryPoint": "run",
  "bindings": [
    {
      "name": "message",
      "type": "queueTrigger",
      "direction": "in",
      "queueName": "myqueue-items",
      "connection": "AzureWebJobsStorage"
    },
    {
      "name": "outputQueue",
      "type": "queue",
      "direction": "out",
      "queueName": "outputqueue",
      "connection": "AzureWebJobsStorage"
    }
  ]
}
                    

Function Runtime and Host

The Azure Functions runtime is responsible for managing the lifecycle of your functions. It includes:

• Host: The application that runs your functions. It manages trigger discovery, event handling, and execution contexts.
• Language Workers: Processes that execute your function code in specific languages (e.g., Node.js, C#, Python, Java).

The runtime communicates with your code through standardized protocols, ensuring portability across different languages and environments.

Statelessness and State Management

Azure Functions are designed to be stateless by default. Each function execution should ideally be independent of previous executions. However, for scenarios requiring state, you can leverage external services like Azure Storage, Cosmos DB, or Azure Durable Functions.