Event triggered functions in GCP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

What happens when a Cloud Function is triggered by a Pub/Sub event?

You have a Google Cloud Function set to trigger on a Pub/Sub topic message. What is the expected behavior when a new message is published to that topic?

A The Cloud Function runs on a fixed schedule unrelated to message publishing.

B The Cloud Function runs once for each message published to the topic.

C The Cloud Function runs only if the message contains a specific attribute named 'trigger'.

D The Cloud Function runs only once regardless of how many messages are published.

💡 Hint

Think about how event-driven systems respond to each event.

Cloud Functions triggered by Pub/Sub run once for each message published to the topic. Each message is an event that causes the function to execute.

❓ Architecture

intermediate

Choosing the right trigger for a Cloud Function

You want to run a Cloud Function whenever a new file is uploaded to a Cloud Storage bucket. Which trigger should you configure?

A Trigger the function on Cloud Storage 'finalize' event.

B Trigger the function on HTTP request.

C Trigger the function on Pub/Sub topic messages.

D Trigger the function on Cloud Scheduler job.

💡 Hint

Consider which event corresponds to file uploads in Cloud Storage.

The 'finalize' event in Cloud Storage triggers when a new object is created or overwritten, which matches file uploads.

❓ security

advanced

Securing event-triggered Cloud Functions

You have a Cloud Function triggered by Pub/Sub messages. How can you ensure only authorized publishers can trigger the function?

A Set IAM permissions so only authorized identities can publish to the Pub/Sub topic.

B Add a secret token in the message payload and verify it inside the function.

C Make the Cloud Function public and rely on message content validation.

D Use a firewall rule to block all incoming traffic except from known IPs.

💡 Hint

Think about controlling who can send messages to the event source.

By restricting who can publish to the Pub/Sub topic via IAM, you control who can trigger the function. This is the recommended security practice.

❓ Configuration

advanced

Handling retries in event-triggered Cloud Functions

You deploy a Cloud Function triggered by Cloud Storage events. If the function fails, what is the default retry behavior?

A The function retries only if manually triggered again.

B The function is never retried; failed executions are discarded immediately.

C The function retries only once after a fixed delay of 5 minutes.

D The function is retried automatically until it succeeds or the event expires.

💡 Hint

Consider how event delivery guarantees work in Cloud Functions.

Cloud Functions triggered by Cloud Storage events automatically retry on failure until the event expires or the function succeeds.

✅ Best Practice

expert

Optimizing Cloud Function cold start times for event triggers

You notice your event-triggered Cloud Function has high cold start latency. Which approach best reduces cold start delays?

A Increase the function timeout to allow longer execution time.

B Disable concurrency to force single execution at a time.

C Keep the function code small and dependencies minimal to speed startup.

D Use a larger memory allocation to slow down the function.

💡 Hint

Think about what affects how fast a function starts.

Smaller code and fewer dependencies reduce the time needed to load and start the function, lowering cold start latency.

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