Azure Functions

# 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())