Pub/Sub triggers

In Cloud Functions, a Pub/Sub trigger enables a function to be called in response to Pub/Sub messages. When you specify a Pub/Sub trigger for a function, you also specify a Pub/Sub topic. Your function will be called whenever a message is published to the specified topic.

For a function to use a Pub/Sub trigger, it must be implemented as an event-driven function:

The Google Events repository contains additional resources for working with event data.

Deployment

You can specify a Pub/Sub trigger when you deploy a function. See Deploy a Cloud Function for general instructions on how to deploy a function, and see below for additional information specific to configuring Pub/Sub triggers during deployment.

gcloud

If you are deploying using the gcloud CLI, the flags shown below are used to configure Pub/Sub triggers:

gcloud functions deploy YOUR_FUNCTION_NAME \
--trigger-topic=YOUR_PUBSUB_TOPIC \
[--retry] \
...
  • The --trigger-topic flag specifies the Pub/Sub topic that the trigger will monitor. Messages published to this topic will trigger calls to your function.
  • The --retry flag controls whether failed function calls are automatically retried. See Retrying event-driven functions for more information.

Legacy Pub/Sub events

Legacy functions in Cloud Functions (1st gen) use a different event type for Pub/Sub triggers:

gcloud functions deploy YOUR_FUNCTION_NAME \
--trigger-event=providers/cloud.pubsub/eventTypes/topic.publish \
--trigger-resource=YOUR_PUBSUB_TOPIC \
...

This event type is supported for legacy functions already consuming these events. However, we recommend using the --trigger-topic flag instead, as the legacy event type might be removed at a future date.

Console

If you are deploying using the Google Cloud console, you can configure a Pub/Sub trigger in the Trigger section.

  • For Cloud Functions (2nd gen):

    1. To add an event trigger, click Add trigger.

    2. Select Pub/Sub trigger.

      The Eventarc trigger pane opens. The pane is pre-populated with Pub/Sub as the event provider, and google.cloud.pubsub.topic.v1.messagePublished as the triggering event.

      You can use the Event field to select a different event.

    3. In the Select a Cloud Pub/Sub topic field, select a topic for the trigger to monitor. Messages published to this topic will trigger calls to your function.

    4. In the Region field, select a location for the Eventarc trigger, if applicable. See Trigger location for more information.

    5. Optionally, in the Service account field, select a service account to be used as the identity of the Eventarc trigger. See Trigger identity for more information.

    6. Select or deselect the Retry on failure checkbox to control whether failed function calls are automatically retried. See Retrying event-driven functions for more information.

    7. Click Save trigger.

  • For Cloud Functions (1st gen):

    1. In the Trigger type field, select Cloud Pub/Sub.
    2. In the Select a Cloud Pub/Sub topic field, select a topic for the trigger to monitor. Messages published to this topic will trigger calls to your function.
    3. Select or deselect the Retry on failure checkbox to control whether failed function calls are automatically retried. See Retrying event-driven functions for more information.

Next steps