Building Serverless Workflows with Durable Functions

How Azure Durable Functions can help you create reliable and robust serverless workflows

Transcript

1. Order from Chaos
   Building Serverless Workflows with
   Durable Functions
   @mark_heath
   https://markheath.net
   

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2. @mark_heath
   Video uploaded Virus Scan File copy
   Extract metadata
   Database
   Audit
   Transcode
   Thumbnail
   Analytics Voice detection Notification
   icons designed by Smashicons from flaticons
   

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3. “Functions as
   a Service”
   (FaaS) A managed platform that
   runs your code (a function)
   in response to an event
   (trigger)
   @mark_heath
   

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4. Blob
   Cosmos DB
   HTTP Request Timer
   Queue
   Azure Functions Triggers
   @mark_heath
   

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5. Serverless
   @mark_heath
   Managed
   Servers
   Automatic
   Scale
   Per-Second
   Billing
   icons designed by Smashicons from flaticons
   

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6. Can we build
   serverless workflows
   with Azure Functions?
   @mark_heath
   

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7. @mark_heath
   Function chaining with queues
   Video
   uploaded
   Extract
   Metadata
   Virus
   Scan
   File
   Copy
   

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8. @mark_heath
   

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9. @mark_heath
   

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10. @mark_heath
    Video uploaded Virus Scan File copy
    Extract metadata
    Database
    Audit
    Transcode
    Thumbnail
    Analytics Voice detection Notification
    icons designed by Smashicons from flaticons
    Can’t see the
    big picture?
    

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11. Image from The Art of Rube Goldberg: (A) Inventive (B) Cartoon (C) Genius, Selected and with commentary by Jennifer
    George; Introduction by Adam Gopnik, Published by Abrams ComicArts.
    

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12. @mark_heath
    Video uploaded Virus Scan File copy
    Extract metadata
    Database
    Audit
    Transcode
    Thumbnail
    Analytics Voice detection Notification
    icons designed by Smashicons from flaticons
    Retries and backoff
    

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13. @mark_heath
    Video uploaded Virus Scan File copy
    Extract metadata
    Database
    Audit
    Transcode
    Thumbnail
    Analytics Voice detection Notification
    icons designed by Smashicons from flaticons
    Error Handling
    Stuck Workflows
    

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14. @mark_heath
    Video uploaded Virus Scan File copy
    Extract metadata
    Database
    Audit
    Transcode
    Thumbnail
    Analytics Voice detection Notification
    icons designed by Smashicons from flaticons
    Waiting for
    external events
    

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15. Fan-out Fan-in Workflow
    @mark_heath
    easy! difficult!
    

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16. Durable Functions
    to the rescue!
    @mark_heath
    

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17. Durable Functions
    • An extension to Azure Functions
    • Microsoft.Azure.WebJobs.Extensions.DurableTask NuGet package
    • C# supported, JavaScript in preview
    • Open source
    • https://github.com/Azure/azure-functions-durable-extension
    @mark_heath
    

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18. Orchestrator Functions
    • Define the steps in the workflow
    • Shows the big picture
    • Calls “activity functions”
    • Or other orchestrators (“sub-orchestrations”)
    • Decides what to do next
    • Handle exceptions across all activities
    • Must adhere to strict rules
    @mark_heath
    

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19. Activity Functions
    • Perform steps in the workflow
    • Can receive input data and return output data
    • Can use “bindings” to connect to external services
    • (Just like a regular Azure Function)
    @mark_heath
    

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20. Task Hubs
    • Stores state associated with workflows
    • Uses an Azure Storage account behind the scenes
    • (Tables and Queues)
    • Uses an event sourcing technique
    @mark_heath
    

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21. REST API
    • Query orchestration status (GET)
    • https://{yourapp}.azurewebsites.net/runtime/webhooks/durabletask/
    instances/{orchestration_id}?taskHub=DurableFunctionsHub&
    connection=Storage&code={code}
    • Send an event to an orchestration (POST)
    • https://{yourapp}.azurewebsites.net/runtime/webhooks/durabletask/
    instances/{orchestration_id}/raiseEvent/{eventName}?
    taskHub=DurableFunctionsHub&connection=Storage&code={code}
    • Terminate an orchestration (POST)
    • https://{yourapp}.azurewebsites.net/runtime/webhooks/durabletask/
    instances/{orchestration_id}/terminate?reason={text}&
    taskHub=DurableFunctionsHub&connection=Storage&code={code}
    

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22. Demo Time!
    @mark_heath
    https://github.com/markheath/durable-functions-ecommerce-sample
    

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23. @mark_heath
    Payment received
    Database
    Generate PDF
    Await approval Email customer
    Generate Video
    

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24. [FunctionName("NewPurchaseWebhook")]
    public static async Task Run(
    [HttpTrigger(AuthorizationLevel.Function, "post", Route = null)] HttpRequest req,
    [OrchestrationClient] DurableOrchestrationClient client)
    {
    string requestBody = await new StreamReader(req.Body).ReadToEndAsync();
    var order = JsonConvert.DeserializeObject(requestBody);
    var orchestrationId = await client.StartNewAsync("O_ProcessOrder", order);
    return new OkResult();
    }
    Starter Function
    @mark_heath
    

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25. Orchestrator V1
    [FunctionName("O_ProcessOrder")]
    public static async Task ProcessOrder(
    [OrchestrationTrigger] DurableOrchestrationContext ctx)
    {
    var order = ctx.GetInput();
    await ctx.CallActivityAsync("A_SaveOrderToDatabase", order);
    var pdfLocation = await ctx.CallActivityAsync("A_CreatePersonalizedPdf", order);
    var videoLocation = await ctx.CallActivityAsync("A_CreateWatermarkedVideo", order);
    await ctx.CallActivityAsync("A_SendEmail", (order, pdfLocation, videoLocation));
    return "Order processed successfully";
    }
    @mark_heath
    

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26. Activity Function
    [FunctionName("A_CreatePersonalizedPdf")]
    public static string CreatePersonalizedPdf(
    [ActivityTrigger] Order order,
    TraceWriter log)
    {
    log.Info("Creating PDF");
    return $"{order.Id}.pdf";
    }
    @mark_heath
    

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27. Orchestrator V2 – Parallel Tasks
    var pdfTask = ctx.CallActivityAsync("A_CreatePersonalizedPdf", order);
    var videoTask = ctx.CallActivityAsync("A_CreateWatermarkedVideo", order);
    await Task.WhenAll(pdfTask, videoTask);
    var pdfLocation = pdfTask.Result;
    var videoLocation = videoTask.Result;
    @mark_heath
    

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28. Exception Handling and Retry
    try
    {
    await ctx.CallActivityAsync
    ("A_CreatePersonalizedPdf", order);
    await ctx.CallActivityWithRetryAsync
    ("A_CreateWatermarkedVideo",
    new RetryOptions(TimeSpan.FromSeconds(30), 3),
    order);
    }
    catch (Exception ex)
    {
    log.Error($"Problem creating media files", ex);
    }
    @mark_heath
    

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29. Waiting for External Events
    var approvalResult = await ctx.WaitForExternalEvent(
    "OrderApprovalResult", TimeSpan.FromMinutes(30),
    "TimedOut");
    if (approvalResult == "TimedOut" ||
    approvalResult == "Rejected")
    {
    await ctx.CallActivityAsync("A_OrderNotApproved", order);
    }
    else
    {
    // order was approved
    await ctx.CallActivityAsync("A_EmailCustomer", order);
    }
    @mark_heath
    

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30. Sending an External Event
    [FunctionName("ApproveOrder")]
    public static async Task ApproveOrder(
    [HttpTrigger(AuthorizationLevel.Function, "post", Route = null)] HttpRequest req,
    [OrchestrationClient] DurableOrchestrationClient client)
    {
    string requestBody = await new StreamReader(req.Body).ReadToEndAsync();
    var approvalResult = JsonConvert.DeserializeObject(requestBody);
    await client.RaiseEventAsync(approvalResult.OrchestrationId,
    "OrderApprovalResult", approvalResult);
    return new OkResult();
    }
    @mark_heath
    

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31. Why Durable Functions?
    • Define the big picture in code
    • Handle errors for the workflow as a whole
    • Retry individual steps with back-off
    • Easily implement waiting for external events with timeout
    • Easily implement fan-out fan-in patterns
    • Track progress of workflows
    • Cancel workflows
    • It’s free and open source
    @mark_heath
    

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32. @mark_heath
    

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33. https://github.com/markheath/
    durable-functions-ecommerce-sample
    https://markheath.net
    @mark_heath
    https://skillsmatter.com/conferences/
    10107-prognet-london-2018#skillscasts
    

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