Durable Functions for workflows in Azure - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are Durable Functions in Azure?

Durable Functions are an extension of Azure Functions that let you write stateful workflows in a serverless environment. They manage state, checkpoints, and restarts automatically.

beginner

What is an orchestrator function in Durable Functions?

An orchestrator function defines the workflow logic. It calls activity functions and manages their execution order, retries, and state without losing progress.

beginner

How do activity functions differ from orchestrator functions?

Activity functions perform the actual tasks or work units. Orchestrator functions coordinate these tasks but do not do the work themselves.

intermediate

Why are Durable Functions good for long-running workflows?

Because they save state and checkpoints, Durable Functions can pause and resume workflows even after restarts or failures, making them reliable for long tasks.

intermediate

What is the role of the Durable Task Framework in Durable Functions?

The Durable Task Framework handles the state, checkpoints, and messaging behind the scenes, so developers can focus on workflow logic without managing infrastructure.

Which function type in Durable Functions manages the workflow logic?

A Orchestrator function

B Activity function

C Trigger function

D HTTP function

The orchestrator function defines and manages the workflow logic by calling activity functions.

What happens if a Durable Function workflow is interrupted?

A It automatically resumes from the last checkpoint

B It loses all progress and restarts from the beginning

C It stops permanently

D It requires manual restart

Durable Functions save checkpoints and state, allowing workflows to resume automatically after interruptions.

Which of these is NOT a benefit of Durable Functions?

A Automatic state management

B Manual server provisioning

C Support for long-running workflows

D Built-in retries and error handling

Durable Functions are serverless and do not require manual server provisioning.

What does an activity function do in Durable Functions?

A Coordinates workflow steps

B Triggers the workflow

C Performs a specific task or action

D Manages checkpoints

Activity functions perform the actual work or tasks called by the orchestrator.

Which Azure service is extended by Durable Functions?

A Azure Logic Apps

B Azure App Service

C Azure Kubernetes Service

D Azure Functions

Durable Functions are an extension of Azure Functions to support stateful workflows.

Explain how Durable Functions manage state and why this is useful for workflows.

Think about what happens if a workflow stops unexpectedly.

Describe the roles of orchestrator and activity functions in a Durable Function workflow.

Compare it to a manager and workers in a team.

Practice

1. What is the main purpose of Durable Functions in Azure?

easy

A. To create virtual machines

B. To store large amounts of data

C. To monitor network traffic

D. To manage long-running workflows reliably

Solution

1. Step 1: Understand Durable Functions role

   Durable Functions are designed to handle workflows that take a long time and need to be reliable.

2. Step 2: Compare options

   Options A, B, and D describe other Azure services, not Durable Functions.

3. Final Answer:

   To manage long-running workflows reliably -> Option D

4. Quick Check:

   Durable Functions = Manage workflows reliably [OK]

Hint: Durable Functions = reliable long workflows [OK]

Common Mistakes:

• Confusing Durable Functions with storage services
• Thinking Durable Functions create VMs
• Assuming Durable Functions monitor networks

2. Which of the following is the correct way to define an orchestrator function in Azure Durable Functions?

easy

A. function orchestrator(context) { /* workflow code */ }

B. function activity(context) { /* workflow code */ }

C. async function orchestrator(context) { /* workflow code */ }

D. async function activity(context) { /* workflow code */ }

Solution

1. Step 1: Identify orchestrator function syntax

   Orchestrator functions must be async to support awaiting activity calls.

2. Step 2: Differentiate activity and orchestrator functions

   Options C and D define activity functions, not orchestrators.

3. Final Answer:

   async function orchestrator(context) { /* workflow code */ } -> Option C

4. Quick Check:

   Orchestrator = async function [OK]

Hint: Orchestrators are async functions [OK]

Common Mistakes:

• Using non-async function for orchestrator
• Confusing activity function syntax with orchestrator
• Omitting async keyword

3. Given the following orchestrator code snippet, what will be the output if the activity function returns 'Hello'?

const result = yield context.callActivity('SayHello');
return result + ' World!';

medium

A. "Hello World!"

B. "World! Hello"

C. "Hello"

D. "World!"

Solution

1. Step 1: Understand callActivity result

   The activity function returns 'Hello', which is assigned to result.

2. Step 2: Concatenate strings

   The orchestrator returns result + ' World!', so 'Hello' + ' World!' = 'Hello World!'.

3. Final Answer:

   "Hello World!" -> Option A

4. Quick Check:

   Result + ' World!' = 'Hello World!' [OK]

Hint: callActivity returns value used in concatenation [OK]

Common Mistakes:

• Reversing string order
• Returning only activity result without addition
• Ignoring yield keyword effect

4. Identify the error in this orchestrator function code:

async function orchestrator(context) {
  const result = context.callActivity('Task');
  return result;
}

medium

A. Function should not be async

B. Missing await or yield before callActivity

C. Incorrect function name

D. callActivity should be called outside orchestrator

Solution

1. Step 1: Check callActivity usage

   callActivity returns a promise and must be awaited or yielded inside orchestrator.

2. Step 2: Identify missing await/yield

   The code calls callActivity without await or yield, causing incorrect behavior.

3. Final Answer:

   Missing await or yield before callActivity -> Option B

4. Quick Check:

   callActivity needs await/yield [OK]

Hint: Always await or yield callActivity in orchestrator [OK]

Common Mistakes:

• Forgetting await/yield on callActivity
• Thinking async keyword is wrong here
• Misplacing callActivity outside orchestrator

5. You want to create a workflow that calls two activity functions in sequence and combines their results. Which orchestrator code correctly implements this?

hard

A. const result1 = await context.callActivity('Activity1');
const result2 = await context.callActivity('Activity2');
return result1 + ' & ' + result2;

B. const result1 = context.callActivity('Activity1');
const result2 = context.callActivity('Activity2');
return result1 + ' & ' + result2;

C. const result1 = await context.callActivity('Activity1');
const result2 = context.callActivity('Activity2');
return result1 + ' & ' + result2;

D. const result1 = context.callActivity('Activity1');
const result2 = await context.callActivity('Activity2');
return result1 + ' & ' + result2;

Solution

1. Step 1: Understand sequential calls in orchestrator

   Each callActivity must be awaited to get the actual result before next call.

2. Step 2: Check options for proper await usage

   Only const result1 = await context.callActivity('Activity1'); const result2 = await context.callActivity('Activity2'); return result1 + ' & ' + result2; awaits both calls, ensuring correct sequence and result combination.

3. Final Answer:

   const result1 = await context.callActivity('Activity1');\nconst result2 = await context.callActivity('Activity2');\nreturn result1 + ' & ' + result2; -> Option A

4. Quick Check:

   Await both activities for correct sequence [OK]

Hint: Await each callActivity for sequential results [OK]

Common Mistakes:

• Not awaiting callActivity causing promises instead of results
• Mixing awaited and non-awaited calls
• Returning promises instead of strings