Durable Functions orchestration patterns in Azure - Commands & Configuration

Introduction

Durable Functions help you run tasks that need to happen in order or repeat over time without losing track. They solve the problem of managing complex workflows in the cloud by keeping track of each step automatically.

When you want to run a series of tasks one after another and keep track of progress even if the system restarts.

When you need to run multiple tasks at the same time and wait for all to finish before moving on.

When you want to run a task repeatedly on a schedule or until a condition is met.

When you want to call a task many times with different inputs and collect all results.

When you want to handle errors and retries automatically in a long-running process.

Config File - function.json

function.json

{
  "bindings": [
    {
      "name": "context",
      "type": "orchestrationTrigger",
      "direction": "in"
    }
  ]
}

This file defines the function as an orchestration trigger, which means it starts and controls the workflow. The context is the object that manages the orchestration state and calls to other functions.

Commands

Starts the orchestration function named 'exampleOrchestrator' to begin the workflow.

Terminal

func durable start new --name exampleOrchestrator

Expected Output

Started orchestration with ID: 12345abcdef

Status: Running

→

--name - Specifies the name of the orchestration function to start

Checks the current status of the orchestration with the given ID to see progress or results.

Terminal

func durable status --id 12345abcdef

Expected Output

Orchestration ID: 12345abcdef

Status: Completed

Output: "Task results collected"

→

--id - Specifies the orchestration instance ID to query

Stops the orchestration with the given ID if you want to cancel the workflow before it finishes.

Terminal

func durable terminate --id 12345abcdef

Expected Output

Orchestration 12345abcdef terminated successfully.

→

--id - Specifies the orchestration instance ID to terminate

Key Concept

If you remember nothing else from this pattern, remember: Durable Functions keep track of each step in a workflow so your tasks run reliably and in order, even if the system restarts.

Common Mistakes

Starting an orchestration without specifying the correct function name

The orchestration will not start because the system cannot find the function to run.

Always use the exact orchestration function name with the --name flag when starting.

Not checking orchestration status after starting

You won't know if the workflow is running, completed, or failed, which can cause confusion.

Use the status command with the orchestration ID to monitor progress.

Terminating an orchestration without confirming the ID

You might stop the wrong workflow or fail to stop the intended one.

Always verify the orchestration ID before terminating.

Summary

Use the start command to begin a Durable Functions orchestration workflow.

Check the status command to monitor the progress and results of the orchestration.

Use the terminate command to stop an orchestration if needed.

Practice

1. What is the main role of an orchestrator function in Azure Durable Functions?

easy

A. To perform the actual work like processing data

B. To coordinate and manage the workflow of multiple tasks

C. To store data permanently in the cloud

D. To send notifications to users

Solution

1. Step 1: Understand the function types in Durable Functions

   Durable Functions use orchestrator functions to manage workflows and activity functions to perform tasks.

2. Step 2: Identify the role of the orchestrator function

   The orchestrator function controls the order and timing of tasks but does not do the actual work itself.

3. Final Answer:

   To coordinate and manage the workflow of multiple tasks -> Option B

4. Quick Check:

   Orchestrator = workflow manager [OK]

Hint: Orchestrator controls flow; activity does the work [OK]

Common Mistakes:

• Confusing orchestrator with activity function
• Thinking orchestrator stores data
• Assuming orchestrator sends notifications

2. Which of the following is the correct way to call an activity function named ProcessOrder from an orchestrator function in C#?

easy

A. await context.CallActivityAsync("ProcessOrder", orderId);

B. context.CallActivity("ProcessOrder", orderId);

C. await CallActivityAsync("ProcessOrder", orderId);

D. context.CallActivityAsync("ProcessOrder");

Solution

1. Step 1: Recall the syntax for calling activity functions

   In Durable Functions, the orchestrator calls activities using await context.CallActivityAsync with the function name and input.

2. Step 2: Check each option for correctness

   await context.CallActivityAsync("ProcessOrder", orderId); uses the correct method with await, context, function name, and input parameter.

3. Final Answer:

   await context.CallActivityAsync("ProcessOrder", orderId); -> Option A

4. Quick Check:

   Correct async call syntax = await context.CallActivityAsync("ProcessOrder", orderId); [OK]

Hint: Use await with context.CallActivityAsync and function name [OK]

Common Mistakes:

• Omitting await keyword
• Using wrong method name like CallActivity
• Missing input parameter when required

3. Given this orchestrator code snippet in JavaScript:

const outputs = [];
outputs.push(await context.callActivity('TaskA', 1));
outputs.push(await context.callActivity('TaskB', 2));
return outputs;

What will the orchestrator return?

medium

A. An array with results from TaskA and TaskB in order

B. A single result from TaskB only

C. An empty array

D. A promise object instead of results

Solution

1. Step 1: Analyze the code execution flow

   The orchestrator calls TaskA and waits for its result, then calls TaskB and waits for its result, pushing both into the outputs array.

2. Step 2: Understand the return value

   Since both calls are awaited, outputs will contain the results of TaskA and TaskB in order.

3. Final Answer:

   An array with results from TaskA and TaskB in order -> Option A

4. Quick Check:

   Awaited calls return results in array [OK]

Hint: Await each call to get results in order [OK]

Common Mistakes:

• Assuming only last result is returned
• Thinking outputs is empty without awaits
• Confusing promise with resolved value

4. You wrote this orchestrator function in C#:

public async Task<string> RunOrchestrator(IDurableOrchestrationContext context)
{
    var result = context.CallActivityAsync<string>("DoWork", null);
    return result.Result;
}

What is the problem with this code?

medium

A. It calls the wrong method for activity

B. It correctly returns the activity result

C. It misses the await keyword causing a compile error

D. It blocks the orchestrator causing a deadlock

Solution

1. Step 1: Identify async call usage

   The code calls CallActivityAsync but does not await it, instead accesses result.Result synchronously.

2. Step 2: Understand deadlock risk in orchestrators

   Accessing Result blocks the thread and can cause deadlocks in async orchestrator functions.

3. Final Answer:

   It blocks the orchestrator causing a deadlock -> Option D

4. Quick Check:

   Use await, not .Result, to avoid deadlocks [OK]

Hint: Always await async calls in orchestrators [OK]

Common Mistakes:

• Using .Result instead of await
• Ignoring async method patterns
• Assuming synchronous access works fine

5. You want to run three activity functions Task1, Task2, and Task3 in parallel and wait for all to finish before continuing. Which orchestrator pattern correctly achieves this in JavaScript Durable Functions?

hard

A. await context.callActivity('Task1');
await context.callActivity('Task2');
await context.callActivity('Task3');

B. const results = [];
results.push(await context.callActivity('Task1'));
results.push(await context.callActivity('Task2'));
results.push(await context.callActivity('Task3'));

C. const tasks = [
context.callActivity('Task1'),
context.callActivity('Task2'),
context.callActivity('Task3')
];
const results = await Promise.all(tasks);

D. const results = await context.callActivity('Task1') + await context.callActivity('Task2') + await context.callActivity('Task3');

Solution

1. Step 1: Understand parallel execution in JavaScript

   To run tasks in parallel, start them without awaiting immediately, collect promises, then await all together.

2. Step 2: Analyze each option

   const tasks = [ context.callActivity('Task1'), context.callActivity('Task2'), context.callActivity('Task3') ]; const results = await Promise.all(tasks); creates an array of promises and awaits them all with Promise.all, running tasks concurrently.

3. Final Answer:

   Use Promise.all with array of activity calls for parallel execution -> Option C

4. Quick Check:

   Parallel = start all, then await all [OK]

Hint: Use Promise.all to await multiple tasks in parallel [OK]

Common Mistakes:

• Awaiting each task sequentially (Options A and C)
• Trying to add awaited results (Option D)
• Not collecting promises before awaiting