Durable Functions orchestration patterns in Azure - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a Durable Functions orchestration.

Azure

const client = df.getClient(context); const instanceId = await client.startNew('[1]', undefined, input);

Drag options to blanks, or click blank then click option'

AhttpStart

BactivityFunction

CtriggerFunction

DorchestratorFunction

Attempts:

3 left

💡 Hint

Common Mistakes

Using the activity function name instead of the orchestrator function name.

Using the HTTP trigger function name here.

The orchestration is started by calling startNew with the name of the orchestrator function.

2fill in blank

medium

Complete the code to call an activity function from an orchestrator.

Azure

const result = yield context.df.callActivity('[1]', input);

Drag options to blanks, or click blank then click option'

AorchestratorFunction

BactivityFunction

ChttpStart

DtimerFunction

Attempts:

3 left

💡 Hint

Common Mistakes

Using the orchestrator function name instead of the activity function name.

Using the HTTP trigger function name.

Inside an orchestrator, you call activity functions by their name using callActivity.

3fill in blank

hard

Fix the error in the orchestration code to wait for multiple activities to complete.

Azure

const tasks = [context.df.callActivity('A', inputA), context.df.callActivity('B', inputB)]; const results = yield [1](tasks);

Drag options to blanks, or click blank then click option'

Acontext.df.Task.whenAll

Bcontext.df.Task.all

Ccontext.df.Task.waitAll

Dcontext.df.Task.waitAny

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-existent method like Task.all or Task.waitAll.

Using Task.waitAny which waits for any one task.

To wait for all tasks to complete, use context.df.Task.whenAll.

4fill in blank

hard

Fill both blanks to create a durable timer that waits for 5 minutes.

Azure

const expiration = context.df.currentUtcDateTime.addMinutes([1]); yield context.df.createTimer([2]);

Drag options to blanks, or click blank then click option'

A5

B10

Cexpiration

Dcontext.df.currentUtcDateTime

Attempts:

3 left

💡 Hint

Common Mistakes

Using 10 minutes instead of 5.

Passing the current time instead of the expiration time to createTimer.

You add 5 minutes to the current time, then create a timer that waits until that expiration time.

5fill in blank

hard

Fill all three blanks to implement a fan-out/fan-in pattern that calls three activities and collects results.

Azure

const tasks = [context.df.callActivity([1], input1), context.df.callActivity([2], input2), context.df.callActivity([3], input3)]; const results = yield context.df.Task.whenAll(tasks);

Drag options to blanks, or click blank then click option'

A'activityOne'

B'activityTwo'

C'activityThree'

D'orchestratorFunction'

Attempts:

3 left

💡 Hint

Common Mistakes

Using the orchestrator function name instead of activity names.

Missing quotes around activity names.

Each activity function is called by its name as a string. The orchestrator function is not called here.

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