azure-functions

What this skill does

# Azure Functions

Expert patterns for Azure Functions development including isolated worker model,
Durable Functions orchestration, cold start optimization, and production patterns.
Covers .NET, Python, and Node.js programming models.

## Patterns

### Isolated Worker Model (.NET)

Modern .NET execution model with process isolation

**When to use**: Building new .NET Azure Functions apps

### Template

// Program.cs - Isolated Worker Model
using Microsoft.Azure.Functions.Worker;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

var host = new HostBuilder()
    .ConfigureFunctionsWorkerDefaults()
    .ConfigureServices(services =>
    {
        // Add Application Insights
        services.AddApplicationInsightsTelemetryWorkerService();
        services.ConfigureFunctionsApplicationInsights();

        // Add HttpClientFactory (prevents socket exhaustion)
        services.AddHttpClient();

        // Add your services
        services.AddSingleton<IMyService, MyService>();
    })
    .Build();

host.Run();

// HttpTriggerFunction.cs
using Microsoft.Azure.Functions.Worker;
using Microsoft.Azure.Functions.Worker.Http;
using Microsoft.Extensions.Logging;

public class HttpTriggerFunction
{
    private readonly ILogger<HttpTriggerFunction> _logger;
    private readonly IMyService _service;

    public HttpTriggerFunction(
        ILogger<HttpTriggerFunction> logger,
        IMyService service)
    {
        _logger = logger;
        _service = service;
    }

    [Function("HttpTrigger")]
    public async Task<HttpResponseData> Run(
        [HttpTrigger(AuthorizationLevel.Function, "get", "post")] HttpRequestData req)
    {
        _logger.LogInformation("Processing request");

        try
        {
            var result = await _service.ProcessAsync(req);

            var response = req.CreateResponse(HttpStatusCode.OK);
            await response.WriteAsJsonAsync(result);
            return response;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error processing request");
            var response = req.CreateResponse(HttpStatusCode.InternalServerError);
            await response.WriteAsJsonAsync(new { error = "Internal server error" });
            return response;
        }
    }
}

### Notes

- In-process model deprecated November 2026
- Isolated worker supports .NET 8, 9, 10, and .NET Framework
- Full dependency injection support
- Custom middleware support

### Node.js v4 Programming Model

Modern code-centric approach for TypeScript/JavaScript

**When to use**: Building Node.js Azure Functions

### Template

// src/functions/httpTrigger.ts
import { app, HttpRequest, HttpResponseInit, InvocationContext } from "@azure/functions";

export async function httpTrigger(
  request: HttpRequest,
  context: InvocationContext
): Promise<HttpResponseInit> {
  context.log(`Http function processed request for url "${request.url}"`);

  try {
    const name = request.query.get("name") || (await request.text()) || "world";

    return {
      status: 200,
      jsonBody: { message: `Hello, ${name}!` }
    };
  } catch (error) {
    context.error("Error processing request:", error);
    return {
      status: 500,
      jsonBody: { error: "Internal server error" }
    };
  }
}

// Register function with app object
app.http("httpTrigger", {
  methods: ["GET", "POST"],
  authLevel: "function",
  handler: httpTrigger
});

// Timer trigger example
app.timer("timerTrigger", {
  schedule: "0 */5 * * * *",  // Every 5 minutes
  handler: async (myTimer, context) => {
    context.log("Timer function executed at:", new Date().toISOString());
  }
});

// Blob trigger example
app.storageBlob("blobTrigger", {
  path: "samples-workitems/{name}",
  connection: "AzureWebJobsStorage",
  handler: async (blob, context) => {
    context.log(`Blob trigger processing: ${context.triggerMetadata.name}`);
    context.log(`Blob size: ${blob.length} bytes`);
  }
});

### Notes

- v4 model is code-centric, no function.json files
- Uses app object similar to Express.js
- TypeScript first-class support
- All triggers registered in code

### Python v2 Programming Model

Decorator-based approach for Python functions

**When to use**: Building Python Azure Functions

### Template

# function_app.py
import azure.functions as func
import logging
import json

app = func.FunctionApp(http_auth_level=func.AuthLevel.FUNCTION)

@app.route(route="hello", methods=["GET", "POST"])
async def http_trigger(req: func.HttpRequest) -> func.HttpResponse:
    logging.info("Python HTTP trigger function processed a request.")

    try:
        name = req.params.get("name")
        if not name:
            try:
                req_body = req.get_json()
                name = req_body.get("name")
            except ValueError:
                pass

        if name:
            return func.HttpResponse(
                json.dumps({"message": f"Hello, {name}!"}),
                mimetype="application/json"
            )
        else:
            return func.HttpResponse(
                json.dumps({"message": "Hello, World!"}),
                mimetype="application/json"
            )
    except Exception as e:
        logging.error(f"Error processing request: {str(e)}")
        return func.HttpResponse(
            json.dumps({"error": "Internal server error"}),
            status_code=500,
            mimetype="application/json"
        )

@app.timer_trigger(schedule="0 */5 * * * *", arg_name="myTimer")
def timer_trigger(myTimer: func.TimerRequest) -> None:
    logging.info("Timer trigger executed")

@app.blob_trigger(arg_name="myblob", path="samples-workitems/{name}",
                  connection="AzureWebJobsStorage")
def blob_trigger(myblob: func.InputStream):
    logging.info(f"Blob trigger: {myblob.name}, Size: {myblob.length} bytes")

@app.queue_trigger(arg_name="msg", queue_name="myqueue",
                   connection="AzureWebJobsStorage")
def queue_trigger(msg: func.QueueMessage) -> None:
    logging.info(f"Queue message: {msg.get_body().decode('utf-8')}")

### Notes

- v2 model uses decorators, no function.json files
- Python runs out-of-process (always isolated)
- Linux-based hosting required for Python
- Async functions supported

### Durable Functions - Function Chaining

Sequential execution with state persistence

**When to use**: Need sequential workflow with automatic retry

### Template

// C# Isolated Worker - Function Chaining
using Microsoft.Azure.Functions.Worker;
using Microsoft.DurableTask;
using Microsoft.DurableTask.Client;

public class OrderWorkflow
{
    [Function("OrderOrchestrator")]
    public static async Task<OrderResult> RunOrchestrator(
        [OrchestrationTrigger] TaskOrchestrationContext context)
    {
        var order = context.GetInput<Order>();

        // Functions execute sequentially, state persisted between each
        var validated = await context.CallActivityAsync<ValidatedOrder>(
            "ValidateOrder", order);

        var payment = await context.CallActivityAsync<PaymentResult>(
            "ProcessPayment", validated);

        var shipped = await context.CallActivityAsync<ShippingResult>(
            "ShipOrder", new ShipRequest { Order = validated, Payment = payment });

        var notification = await context.CallActivityAsync<bool>(
            "SendNotification", shipped);

        return new OrderResult
        {
            OrderId = order.Id,
            Status = "Completed",
            TrackingNumber = shipped.TrackingNumber
        };
    }

    [Function("ValidateOrder")]
    public static async Task<ValidatedOrder> ValidateOrder(
        [ActivityTrigger] Order order, FunctionContext context)
    {
        var logger = context.GetLogger<OrderWorkflow>();
        logger.LogInformation("Validating order {OrderId}", order.Id);

        // Validation logic...
        return new ValidatedOrder { /* ... */ };
    }

    [Function("ProcessPayment")]
    public static async Tas