Azure Functions

// Program.cs
var host = new HostBuilder()
    .ConfigureFunctionsWebApplication()
    .ConfigureServices(services =>
    {
        services.AddApplicationInsightsTelemetryWorkerService();
        services.ConfigureFunctionsApplicationInsights();
        services.AddSingleton<IMyService, MyService>();
    })
    .Build();

host.Run();

public class HttpFunctions(ILogger<HttpFunctions> logger, IMyService myService)
{
    [Function("GetItems")]
    public async Task<IActionResult> GetItems(
        [HttpTrigger(AuthorizationLevel.Function, "get", Route = "items")] HttpRequest req)
    {
        logger.LogInformation("Processing GetItems request");
        var items = await myService.GetItemsAsync();
        return new OkObjectResult(items);
    }
}

public class QueueFunctions(ILogger<QueueFunctions> logger, IOptions<ProcessingOptions> options)
{
    [Function("ProcessMessage")]
    public async Task ProcessMessage(
        [QueueTrigger("myqueue", Connection = "AzureWebJobsStorage")] string message)
    {
        logger.LogInformation("Processing message: {Message}", message);
        // Process with retry policy from options
    }
}

// Program.cs
var host = new HostBuilder()
    .ConfigureFunctionsWebApplication(builder =>
    {
        builder.UseMiddleware<ExceptionHandlingMiddleware>();
        builder.UseMiddleware<CorrelationIdMiddleware>();
    })
    .Build();

// CorrelationIdMiddleware.cs
public class CorrelationIdMiddleware : IFunctionsWorkerMiddleware
{
    public async Task Invoke(FunctionContext context, FunctionExecutionDelegate next)
    {
        var correlationId = context.Features.Get<IHttpRequestFeature>()?.Headers["X-Correlation-Id"]
            ?? Guid.NewGuid().ToString();

        context.Items["CorrelationId"] = correlationId;

        await next(context);
    }
}

[Function(nameof(ChainOrchestrator))]
public static async Task<string> ChainOrchestrator(
    [OrchestrationTrigger] TaskOrchestrationContext context)
{
    var result1 = await context.CallActivityAsync<string>(nameof(Step1), "input");
    var result2 = await context.CallActivityAsync<string>(nameof(Step2), result1);
    var result3 = await context.CallActivityAsync<string>(nameof(Step3), result2);
    return result3;
}

[Function(nameof(Step1))]
public static string Step1([ActivityTrigger] string input) => $"Step1({input})";

[Function(nameof(Step2))]
public static string Step2([ActivityTrigger] string input) => $"Step2({input})";

[Function(nameof(Step3))]
public static string Step3([ActivityTrigger] string input) => $"Step3({input})";

[Function(nameof(FanOutFanInOrchestrator))]
public static async Task<int[]> FanOutFanInOrchestrator(
    [OrchestrationTrigger] TaskOrchestrationContext context)
{
    var workItems = await context.CallActivityAsync<string[]>(nameof(GetWorkItems), null);

    // Fan out - process all items in parallel
    var tasks = workItems.Select(item =>
        context.CallActivityAsync<int>(nameof(ProcessWorkItem), item));

    // Fan in - wait for all to complete
    var results = await Task.WhenAll(tasks);

    return results;
}

[Function(nameof(ProcessWorkItem))]
public static int ProcessWorkItem([ActivityTrigger] string item)
{
    // Process item and return result
    return item.Length;
}

[Function(nameof(ApprovalOrchestrator))]
public static async Task<string> ApprovalOrchestrator(
    [OrchestrationTrigger] TaskOrchestrationContext context)
{
    var request = context.GetInput<ApprovalRequest>();

    // Send notification
    await context.CallActivityAsync(nameof(SendApprovalRequest), request);

    // Wait for external event with timeout
    using var cts = new CancellationTokenSource();
    var approvalTask = context.WaitForExternalEvent<bool>("ApprovalEvent");
    var timeoutTask = context.CreateTimer(context.CurrentUtcDateTime.AddDays(7), cts.Token);

    var winner = await Task.WhenAny(approvalTask, timeoutTask);

    if (winner == approvalTask)
    {
        cts.Cancel();
        return approvalTask.Result ? "Approved" : "Rejected";
    }

    return "Timed out";
}