Triggering a Cloud Function with Cloud Pub/Sub

30 minutes
  • 7 Learning Objectives

About this Hands-on Lab

Cloud Functions can be triggered in two ways: through a direct HTTP request or through a background event. One of the most frequently used services for background events is Cloud Pub/Sub, Google Cloud’s platform-wide messaging service. In this pairing, Cloud Functions becomes a direct subscriber to a specific Cloud Pub/Sub topic, which allows code to be run whenever a message is received on a specific topic. In this hands-on lab, we’ll walk through the entire experience, from setup to confirmation.

Learning Objectives

Successfully complete this lab by achieving the following learning objectives:

Enable required APIs.
  1. Use the API Library to find and enable the Cloud Pub/Sub API.
  2. Use the API Library to find and enable the Cloud Functions API.
  3. Use the API Library to find and enable the Cloud Build API.
Create Pub/Sub topic.
  1. From the main console navigation, go to Cloud Pub/Sub.
  2. Click Create a topic.
  3. In the dialog, enter a name greetings for the topic.
  4. Click Create.
Create a Cloud Function.
  1. From the main console, go to Cloud Functions.
  2. Click Create function.
  3. Configure the function with the following values:
    • Name: la-pubsub-function
    • Trigger: Cloud Pub/Sub
    • Topic: greetings
    • Source code: Inline editor
    • Runtime: Python 3.7
  4. In the main.py field, enter the following code:
import base64

def greetings_pubsub(data, context):

    if 'data' in data:
        name = base64.b64decode(data['data']).decode('utf-8')
    else:
        name = 'folks'
    print('Greetings {} from Linux Academy!'.format(name))
  1. Set Function to Execute to greetings_pubsub.
  2. Click Create.
Publish message to topic from console.
  1. Click the newly created Cloud Function name.
  2. Switch to Trigger.
  3. Click the topic link to go to the Cloud Pub/Sub topic.
  4. From the Topic page, click Publish Message.
  5. In the Message field, enter everyone around the world.
  6. Click Publish.
Confirm Cloud Function execution.
  1. Return to the Cloud Functions dashboard.
  2. Click the Cloud Function’s name.
  3. From the Cloud Function navigation, click View Logs.
  4. Locate the most recent log.
  5. Confirm function execution.
Trigger Cloud Function directly from command line.
  1. Click Activate Cloud Shell from the top row of the console.

  2. In the Cloud Shell, enter the following code:

    DATA=$(printf 'my friends' | base64)
    gcloud functions call la-pubsub-function --data '{"data":"'$DATA'"}'
  3. After a moment, refresh the logs page and confirm the Cloud Function execution.

Publish message to topic from command line.
  1. In the Cloud Shell, enter the following command:

    gcloud pubsub topics publish greetings --message "y'all"
  2. After a moment, refresh the log page to confirm the function has executed.

Additional Resources

You’ve been asked to lay the groundwork for one aspect of the new app that relies on code being executed when a message is received from any number of outlets. To do this, you’ll need to establish a Cloud Pub/Sub topic and then create an example Cloud Function that uses the topic as a trigger. Naturally, you’ll need to confirm the Cloud Function has successfully executed.

You’ll need to accomplish the following steps to complete your task:

  1. Enable APIs.
  2. Create Pub/Sub topic.
  3. Create Cloud Function.
  4. Publish message on topic.
  5. Confirm Cloud Function executed via logs.
  6. Trigger directly via the command line.
  7. Confirm Cloud Function executed via logs.
  8. Send message to topic from command line.
  9. Confirm Cloud Function executed via logs.

Note: In addition to the lab mentioned libraries, use the API Library to find and enable the Cloud Build API.

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