Google Cloud Storage Triggers

Cloud Functions can respond to change notifications emerging from Google Cloud Storage. These notifications can be configured to trigger in response to various events inside a bucket—object creation, deletion, archiving and metadata updates.

Cloud Storage Event Types

Cloud Storage events used by Cloud Functions are based on Cloud Pub/Sub Notifications for Google Cloud Storage and can be set configured in similar way.

Supported trigger type values are:





Object Finalize

Trigger type value:

This event is sent when a new object is created (or an existing object is overwritten, and a new generation of that object is created) in the bucket.

For example:


 * Generic background Cloud Function to be triggered by Cloud Storage.
 * @param {object} event The Cloud Functions event.
 * @param {function} callback The callback function.
exports.helloGCSGeneric = (event, callback) => {
  const file =;

  console.log(`  Event ${event.eventId}`);
  console.log(`  Event Type: ${event.eventType}`);
  console.log(`  Bucket: ${file.bucket}`);
  console.log(`  File: ${}`);
  console.log(`  Metageneration: ${file.metageneration}`);
  console.log(`  Created: ${file.timeCreated}`);
  console.log(`  Updated: ${file.updated}`);


The helloGCSGeneric function is exported by the module and is executed when a new object is finalized in a bucket. To deploy, run the following command in the directory that contains your function:

gcloud beta functions deploy helloGCSGeneric --trigger-resource [YOUR_TRIGGER_BUCKET_NAME] --trigger-event


  • [YOUR_TRIGGER_BUCKET_NAME] is the name of the Cloud Storage Bucket that the function will monitor.

Object Delete

Trigger type value:

This event is sent when an object is permanently deleted. Depending on the object versioning setting for a bucket this means:

  • For versioning buckets, this is only sent when a version is permanently deleted (but not when an object is archived).

  • For non-versioning buckets, this is sent when an object is deleted or overwritten.

Object Archive

Trigger type value:

This event is sent when a live version of an object is archived or deleted.

This event is only sent for versioning buckets.

Object Metadata Update

Trigger type value:

This event is sent when the metadata of an existing object changes.

Event delivery mechanism

The events are delivered with Pub/Sub notifications from Cloud Storage. Setting up too many functions against the same bucket may exhaust the notification limit for the bucket and make it impossible to create the function, as indicated by the error Cloud Storage bucket ...: Pub/Sub notification limit reached. See Google Cloud Storage Cloud Pub/Sub Notifications documentation for more information about notification limits.

Legacy Cloud Storage triggers

The gcloud command below deploys a function that is triggered by legacy object change notifications on a specific bucket. Generally, Cloud Pub/Sub Notifications are easier to use, more flexible, and more powerful than object change notifications. However, these legacy notifications are supported for legacy functions already consuming these events.

gcloud beta functions deploy [YOUR_FUNCTION_NAME] --trigger-resource [YOUR_TRIGGER_BUCKET_NAME] --trigger-event providers/
Argument Description
--trigger-resource <name> The name of the Cloud Storage bucket the function watches for changes.
--trigger-event <name> The name of the event type that the function wishes to receive. In this case, it is the legacy object.change event.

Next steps

See the Cloud Storage Tutorial for an example of how to implement a background function that is triggered by Cloud Storage.

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