Event triggered functions in GCP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an event triggered function in Google Cloud?

An event triggered function runs automatically when a specific event happens, like a file upload or a message arrival. It reacts to changes without needing manual start.

beginner

Name two common event sources for Google Cloud Functions.

1. Cloud Storage (e.g., file upload)
2. Pub/Sub (message arrival)
These trigger functions to run when events happen.

beginner

How does an event triggered function differ from an HTTP triggered function?

Event triggered functions run automatically on events like file changes or messages. HTTP triggered functions run only when someone sends an HTTP request.

beginner

What is a practical example of using an event triggered function?

Automatically resizing images when a new photo is uploaded to Cloud Storage. The upload event triggers the function to process the image.

beginner

Why are event triggered functions useful in cloud architecture?

They allow automation and real-time response without manual intervention, saving time and resources by reacting only when needed.

Which of these can trigger a Google Cloud event triggered function?

A A user clicking a button on a website

B A manual command in the terminal

C A new file uploaded to Cloud Storage

D A scheduled timer only

Event triggered functions respond to events like file uploads, not manual commands or user clicks directly.

What type of event source is Pub/Sub in Google Cloud Functions?

A File storage event source

B Message queue event source

C HTTP request event source

D Database change event source

Pub/Sub is a messaging service that triggers functions when messages arrive.

How does a Cloud Function know when to run if it is event triggered?

A It runs only when manually started

B It runs every hour automatically

C It waits for a user to press a button

D It listens for specific events configured during setup

Event triggered functions are set up to listen for specific events and run automatically when those happen.

Which is NOT a benefit of event triggered functions?

A Manual start required every time

B Enables real-time automation

C Saves resources by running only when needed

D Automatic response to events

Event triggered functions do NOT require manual start; they run automatically.

What happens if an event triggered function fails during execution?

A It can be retried automatically depending on configuration

B It never runs again

C It sends an email to all users

D It shuts down the entire cloud project

Google Cloud Functions can be configured to retry on failure to ensure the event is processed.

Explain how event triggered functions work in Google Cloud and give an example use case.

Think about what happens when a file is uploaded or a message arrives.

Describe the benefits of using event triggered functions in cloud applications.

Consider how automation saves time and resources.

Practice

1. What is the main purpose of an event triggered function in Google Cloud Functions?

easy

A. To store data permanently in the cloud

B. To manually start a function from the console

C. To schedule functions to run at fixed times

D. To automatically run code when a specific event occurs

Solution

1. Step 1: Understand event triggered functions

   Event triggered functions run automatically when a specific event happens, like a file upload or database change.

2. Step 2: Compare options with the definition

   Only To automatically run code when a specific event occurs describes automatic running on events. Options B and C describe manual or scheduled runs, and D is unrelated.

3. Final Answer:

   To automatically run code when a specific event occurs -> Option D

4. Quick Check:

   Event triggered function = automatic run on event [OK]

Hint: Event triggered means automatic run on event [OK]

Common Mistakes:

• Confusing event triggered with scheduled functions
• Thinking manual start is event triggered
• Mixing storage with function triggers

2. Which of the following is the correct way to specify a Cloud Function triggered by a Cloud Storage event in deployment?

easy

A. gcloud functions deploy myFunc --trigger-resource my-bucket --trigger-event google.storage.object.finalize

B. gcloud functions deploy myFunc --trigger-topic myTopic

C. gcloud functions deploy myFunc --trigger-http

D. gcloud functions deploy myFunc --trigger-schedule "every 5 minutes"

Solution

1. Step 1: Identify Cloud Storage event trigger syntax

   Cloud Storage events use --trigger-resource for the bucket and --trigger-event for the event type like object finalize.

2. Step 2: Match options with correct syntax

   gcloud functions deploy myFunc --trigger-resource my-bucket --trigger-event google.storage.object.finalize correctly uses --trigger-resource and --trigger-event for Cloud Storage. Others are for HTTP, Pub/Sub, or scheduled triggers.

3. Final Answer:

   gcloud functions deploy myFunc --trigger-resource my-bucket --trigger-event google.storage.object.finalize -> Option A

4. Quick Check:

   Cloud Storage trigger = resource + event flags [OK]

Hint: Storage triggers need resource and event flags [OK]

Common Mistakes:

• Using --trigger-http for storage events
• Confusing Pub/Sub topic triggers with storage
• Using schedule flags for event triggers

3. Consider this Cloud Function triggered by a Pub/Sub topic named 'updates'. What will happen when a message is published to 'updates'?

exports.processUpdate = (event, context) => {
  const message = Buffer.from(event.data, 'base64').toString();
  console.log(`Received message: ${message}`);
};

medium

A. The function ignores the message and does nothing

B. The function throws an error due to missing parameters

C. The function logs the decoded message content

D. The function logs the raw base64 message without decoding

Solution

1. Step 1: Understand event data decoding

   The function decodes the base64 event.data to a string and logs it.

2. Step 2: Check function behavior on message publish

   When a message is published, the function runs and logs the decoded message content.

3. Final Answer:

   The function logs the decoded message content -> Option C

4. Quick Check:

   Pub/Sub event data decoded and logged [OK]

Hint: Pub/Sub data is base64 decoded before use [OK]

Common Mistakes:

• Forgetting to decode base64 data
• Assuming function errors without checking code
• Thinking function ignores messages

4. You deployed a Cloud Function triggered by Firestore document creation, but it never runs. Which of these is the most likely cause?

medium

A. The function is missing the correct Firestore trigger path

B. The function code has a syntax error preventing deployment

C. The Cloud Function is set to trigger on HTTP instead of Firestore

D. The Firestore database is empty

Solution

1. Step 1: Check trigger configuration

   If the trigger path is incorrect, the function won't run on document creation events.

2. Step 2: Eliminate other causes

   Syntax errors prevent deployment (not silent failure). HTTP trigger won't respond to Firestore events. Firestore being empty doesn't stop triggers on new documents.

3. Final Answer:

   The function is missing the correct Firestore trigger path -> Option A

4. Quick Check:

   Wrong trigger path = no function run [OK]

Hint: Check trigger path matches Firestore event exactly [OK]

Common Mistakes:

• Assuming empty Firestore blocks triggers
• Confusing HTTP triggers with event triggers
• Ignoring trigger path correctness

5. You want to create a Cloud Function that triggers when a new file is uploaded to any folder inside a Cloud Storage bucket named 'photos'. Which trigger configuration is correct?

hard

A. Use --trigger-resource photos and --trigger-event google.storage.object.metadataUpdate

B. Use --trigger-resource photos and --trigger-event google.storage.object.finalize

C. Use --trigger-resource photos and --trigger-event google.storage.object.archive

D. Use --trigger-resource photos/* and --trigger-event google.storage.object.delete

Solution

1. Step 1: Identify correct event for new file upload

   The event google.storage.object.finalize triggers when a new object is created or overwritten.

2. Step 2: Confirm resource and event usage

   The resource is the bucket name 'photos'. Wildcards like 'photos/*' are not valid for --trigger-resource.

3. Final Answer:

   Use --trigger-resource photos and --trigger-event google.storage.object.finalize -> Option B

4. Quick Check:

   New file upload = finalize event on bucket resource [OK]

Hint: Use bucket name and finalize event for new uploads [OK]

Common Mistakes:

• Using delete or archive events instead of finalize
• Trying to use wildcards in trigger-resource
• Using metadataUpdate event which triggers on metadata changes