Why Event triggered functions in GCP? - Purpose & Use Cases

The Big Idea

What if your app could instantly react to anything happening, without you lifting a finger?

The Scenario

Imagine you have a website where users upload photos. Every time a photo is uploaded, you want to resize it and save a thumbnail. Doing this manually means constantly checking for new uploads and running resizing tasks yourself.

The Problem

Manually watching for new uploads wastes time and energy. You might miss some uploads or resize the same photo twice. It's slow, error-prone, and you have to keep your computer running all the time.

The Solution

Event triggered functions automatically run your code when something happens, like a new photo upload. You don't have to watch or check anything. The cloud service listens for events and runs your function instantly and reliably.

Before vs After

✗ Before

while True:
  if new_file_uploaded():
    resize_image()
  sleep(10)

✓ After

def on_file_upload(event):
  resize_image(event.file)

What It Enables

You can build apps that react instantly to changes without wasting resources or missing important events.

Real Life Example

When a user uploads a document to cloud storage, an event triggered function can automatically convert it to PDF and send a notification email.

Key Takeaways

Manual checking for events is slow and unreliable.

Event triggered functions run code automatically when something happens.

This makes apps faster, more efficient, and easier to maintain.

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