Event triggered functions in GCP - Commands & Configuration

Introduction

Event triggered functions run automatically when something happens, like a file upload or a message arrival. They help you react quickly without checking all the time.

When you want to process images right after they are uploaded to cloud storage.

When you need to update a database after a new message arrives in a queue.

When you want to send notifications automatically after a user signs up.

When you want to clean up resources after a file is deleted.

When you want to trigger workflows based on changes in cloud services.

Config File - function.yaml

function.yaml

name: projects/example-project/locations/us-central1/functions/my-function
runtime: python39
entryPoint: hello_world
eventTrigger:
  eventType: google.storage.object.finalize
  resource: projects/_/buckets/my-bucket
failurePolicy:
  retry: {}

name: The full path to your function in your project and region.

runtime: The language and version your function uses.

entryPoint: The function name in your code that runs when triggered.

eventTrigger: Defines what event starts the function. Here, it triggers when a file is added to the bucket 'my-bucket'.

failurePolicy: Tells the system to retry if the function fails.

Commands

Deploys the function named 'my-function' to Google Cloud. It sets the runtime to Python 3.9, triggers on new files in 'my-bucket', and uses 'hello_world' as the function to run.

Terminal

gcloud functions deploy my-function --runtime python39 --trigger-resource my-bucket --trigger-event google.storage.object.finalize --entry-point hello_world --region us-central1 --project example-project

Expected Output

Deploying function (may take a while)...

Deploying function (my-function)...done.



availableMemoryMb: 256

entryPoint: hello_world

httpsTrigger: {}

name: projects/example-project/locations/us-central1/functions/my-function

runtime: python39

status: ACTIVE

trigger:

  eventType: google.storage.object.finalize

  resource: projects/_/buckets/my-bucket

updateTime: '2024-06-01T12:00:00Z'

versionId: '1'

→

--runtime - Specifies the language and version for the function.

→

--trigger-resource - Sets the cloud resource that triggers the function.

→

--trigger-event - Defines the event type that triggers the function.

Shows details about the deployed function to confirm it is set up correctly and active.

Terminal

gcloud functions describe my-function --region us-central1 --project example-project

Expected Output

name: projects/example-project/locations/us-central1/functions/my-function

status: ACTIVE

entryPoint: hello_world

runtime: python39

trigger:

  eventType: google.storage.object.finalize

  resource: projects/_/buckets/my-bucket

updateTime: '2024-06-01T12:00:00Z'

versionId: '1'

Uploads a file named 'sample-image.png' to the bucket 'my-bucket' to trigger the function.

Terminal

gsutil cp sample-image.png gs://my-bucket/

Expected Output

Copying file://sample-image.png [Content-Type=image/png]...

/ [1 files][  123 KiB/  123 KiB] 100% Done

Operation completed over 1 objects/123 KiB.

Reads the last 5 log entries from the function to see if it ran after the file upload.

Terminal

gcloud functions logs read my-function --region us-central1 --project example-project --limit 5

Expected Output

2024-06-01 12:01:00 my-function: Function execution started

2024-06-01 12:01:01 my-function: Processing file sample-image.png

2024-06-01 12:01:02 my-function: Function execution finished successfully

→

--limit - Limits the number of log entries shown.

Key Concept

If you remember nothing else from this pattern, remember: event triggered functions run automatically when specific cloud events happen, so you don't have to check manually.

Common Mistakes

Using the wrong event type or resource name when deploying the function.

The function will not trigger because it listens to the wrong event or resource.

Double-check the event type and resource name match exactly what you want to trigger on.

Not specifying the correct entry point function name in the deployment.

The cloud platform won't find the function to run, causing errors.

Ensure the entry point matches the function name in your code exactly.

Uploading files to the wrong bucket or region.

The function won't trigger because the event never happens on the expected resource.

Verify the bucket name and region match the trigger settings.

Summary

Deploy the function with the correct runtime, trigger event, and entry point.

Verify the function is active and correctly configured using describe command.

Trigger the function by performing the event, like uploading a file to the bucket.

Check function logs to confirm it ran and processed the event.

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