How does orchestrator replay work?

Orchestrator functions must be deterministic because the Durable Task Framework replays them from the beginning whenever they resume after waiting for an activity, timer, or external event. During replay, previously completed activity results are returned from the history table without re-executing. This means you must never use non-deterministic operations (random numbers, current time, GUID generation, HTTP calls) directly in orchestrator code — instead, use activity functions for any non-deterministic work. The framework provides deterministic alternatives like currentUtcDateTime for timestamps.

What is the difference between sub-orchestrations and activity functions?

Activity functions are single units of work — they run once, produce a result, and have no orchestration capabilities. Sub-orchestrations are full orchestrator functions called from a parent orchestrator, enabling composition of complex workflows from reusable pieces. Sub-orchestrations can contain their own activity calls, timers, waits for external events, and even nested sub-orchestrations. Use activity functions for individual tasks (send email, process file) and sub-orchestrations for reusable workflow segments (order processing pipeline, multi-step approval chain).

Durable Functions Builder

ServerlessAzure

Build Durable Functions orchestration patterns with activities and sub-orchestrations.

Durable Functions Configuration

Build Durable Functions orchestration configs with activities, sub-orchestrations, timers, and retry policies.

Required Fields

orchestrationNamefunctionAppNametaskHubNameorchestration.patternorchestration.activities

{
  "orchestrationName": "OrderProcessingOrchestrator",
  "functionAppName": "func-orders-prod",
  "resourceGroup": "rg-serverless",
  "taskHubName": "OrdersTaskHub",
  "durableTaskVersion": "2.x",
  "storageProvider": {
    "type": "AzureStorage",
    "connectionStringName": "AzureWebJobsStorage",
    "partitionCount": 4
  },
  "orchestration": {
    "pattern": "FunctionChaining",
    "activities": [
      {
        "name": "ValidateOrder",
        "type": "Activity",
        "input": "OrderRequest",
        "output": "ValidationResult",
        "retryPolicy": {
          "maxNumberOfAttempts": 3,
          "firstRetryIntervalInSeconds": 5,
          "backoffCoefficient": 2.0,
          "maxRetryIntervalInSeconds": 60
        }
      },
      {
        "name": "ReserveInventory",
        "type": "Activity",
        "input": "OrderDetails",
        "output": "ReservationResult",
        "retryPolicy": {
          "maxNumberOfAttempts": 5,
          "firstRetryIntervalInSeconds": 10,
          "backoffCoefficient": 2.0,
          "maxRetryIntervalInSeconds": 120
        }
      },
      {
        "name": "ProcessPayment",
        "type": "Activity",
        "input": "PaymentRequest",
        "output": "PaymentResult",
        "retryPolicy": {
          "maxNumberOfAttempts": 3,
          "firstRetryIntervalInSeconds": 15,
          "backoffCoefficient": 2.0,
          "maxRetryIntervalInSeconds": 300
        }
      },
      {
        "name": "SendConfirmation",
        "type": "Activity",
        "input": "OrderConfirmation",
        "output": "NotificationResult"
      }
    ],
    "subOrchestrations": [
      {
        "name": "ShippingSubOrchestrator",
        "pattern": "FanOutFanIn",
        "fanOutActivities": ["GetShippingQuotes", "CalculateTax", "ValidateAddress"]
      }
    ],
    "timers": [
      {
        "name": "PaymentTimeout",
        "duration": "PT30M",
        "description": "Cancel order if payment not received within 30 minutes"
      }
    ],
    "externalEvents": [
      {
        "name": "ApprovalEvent",
        "timeout": "PT24H",
        "description": "Wait for manager approval on high-value orders"
      }
    ]
  },
  "hostSettings": {
    "maxConcurrentActivityFunctions": 10,
    "maxConcurrentOrchestratorFunctions": 5,
    "extendedSessionsEnabled": true,
    "extendedSessionIdleTimeoutInSeconds": 30
  }
}

Generated Output

Output will appear here...

About This Tool

Azure Durable Functions is an extension of Azure Functions that lets you write stateful, long-running workflows in code using orchestrator functions. Instead of managing state machines or queues yourself, you define orchestration logic in C#, JavaScript, Python, or Java, and the Durable Task Framework handles state persistence, checkpointing, and replay. The framework supports patterns like function chaining, fan-out/fan-in, async HTTP APIs, monitoring (polling), and human interaction (approval workflows). The Durable Functions Builder helps you configure orchestration patterns with activity functions, sub-orchestrations, timers, and external event handling.

When to Use This Tool

•Building fan-out/fan-in orchestrations that process thousands of items in parallel and aggregate the results
•Creating long-running approval workflows that wait for external events with configurable timeouts
•Defining monitor patterns that poll an external API at configurable intervals until a condition is met
•Configuring orchestration chaining patterns with error handling and compensation logic for saga transactions

Frequently Asked Questions

How does orchestrator replay work?: Orchestrator functions must be deterministic because the Durable Task Framework replays them from the beginning whenever they resume after waiting for an activity, timer, or external event. During replay, previously completed activity results are returned from the history table without re-executing. This means you must never use non-deterministic operations (random numbers, current time, GUID generation, HTTP calls) directly in orchestrator code — instead, use activity functions for any non-deterministic work. The framework provides deterministic alternatives like currentUtcDateTime for timestamps.
What is the difference between sub-orchestrations and activity functions?: Activity functions are single units of work — they run once, produce a result, and have no orchestration capabilities. Sub-orchestrations are full orchestrator functions called from a parent orchestrator, enabling composition of complex workflows from reusable pieces. Sub-orchestrations can contain their own activity calls, timers, waits for external events, and even nested sub-orchestrations. Use activity functions for individual tasks (send email, process file) and sub-orchestrations for reusable workflow segments (order processing pipeline, multi-step approval chain).

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