Automated GCS Object Scanning Using DLP with Notifications Using Slack

This is a follow up to a previous blog, Google Cloud Storage Object Notifications using Slack in which we used Slack to notify us of new objects being uploaded to GCS.

In this article we will take things a step further, where uploading an object to a GCS bucket will trigger a DLP inspection of the object and if any preconfigured info types (such as credit card numbers or API credentials) are present in the object, a Slack notification will be generated.

As DLP scans are “jobs”, meaning they run asynchronously, we will need to trigger scans and inspect results using two separate Cloud Functions (one for triggering a scan [gcs-dlp-scan-trigger] and one for inspecting the results of the scan [gcs-dlp-evaluate-results]) and a Cloud PubSub topic [dlp-scan-topic] which is used to hold the reference to the DLP job.

The process is described using the sequence diagram below:

The Code

The gcs-dlp-scan-trigger Cloud Function fires when a new object is created in a specified GCS bucket. This function configures the DLP scan to be executed, including the DLP info types (for instance CREDIT_CARD_NUMBER, EMAIL_ADDRESS, ETHNIC_GROUP, PHONE_NUMBER, etc) a and likelihood of that info type existing (for instance LIKELY). DLP scans determine the probability of an info type occurring in the data, they do not scan every object in its entirety as this would be too expensive.

The primary function executed in the gcs-dlp-scan-trigger Cloud Function is named inspect_gcs_file. This function configures and submits the DLP job, supplying a PubSub topic to which the DLP Job Name will be written, the code for the inspect_gcs_file is shown here:

At this stage the DLP job is created an running asynchronously, the next Cloud Function, gcs-dlp-evaluate-results, fires when a message is sent to the PubSub topic defined in the DLP job. The gcs-dlp-evaluate-results reads the DLP Job Name from the PubSub topic, connects to the DLP service and queries the job status, when the job is complete, this function checks the results of the scan, if the min_likliehood threshold is met for any of the specified info types, a Slack message is generated. The code for the main method in the gcs-dlp-evaluate-results function is shown here:

Finally, a Slack webhook is used to send the message to a specified Slack channel in a workspace, this is done using the send_slack_notification function shown here:

An example Slack message is shown here:

839Slack Notification for Sensitive Data Detected in a Newly Created GCS Object

Full source code can be found at:

Google Cloud Storage Object Notifications using Slack

This article describes the steps to integrate Slack with Google Cloud Functions to get notified about object events within a specified Google Cloud Storage bucket.

Google Cloud Storage Object Notifications using Slack

Events could include the creation of new objects, as well as delete, archive or metadata operations performed on a given bucket.

This pattern could be easily extended to other event sources supported by Cloud Functions including:

  • Cloud Pub/Sub messages
  • Cloud Firestore and Firebase events
  • Stackdriver log entries

More information can be found at

The prerequisite steps to configure Slack are provided here:

1. First you will need to create a Slack app (assuming you have already set up an account and a workspace). The following screenshots demonstrate this process:

Create a Slack app
Give the app a name and associate it with an existing Slack workspace

2. Next you need to Enable and Activate Incoming Webhooks to your app and add this to your workspace. The following screenshots demonstrate this process:

Enable Incoming Web Hooks for the app
Activate incoming webhooks
Add the webhook to your workspace

3. Next you need to specify a channel for notifications generated from object events.

Select a channel for the webhook

4. Now you need to copy the Webhook url provided, you will use this later in your Cloud Function.

Copy the webhook URL to the clipboard

Treat your webhook url as a secret, do not upload this to a public source code repository

Next you need to create your Cloud Function, this example uses Python but you can use an alternative runtime including Node.js or Go.

This example templates the source code using the Terraform template_file data source. The function source code is shown here:

Within your Terraform code you need to render your Cloud Function code substituting the slack_webhook_url for it’s value which you will supply as a Terraform variable. The rendered template file is then placed in a local directory along with a requirements.txt file and zipped up. The resulting Zip archive is uploaded to a specified bucket where it will be sourced to create the Cloud Function.

Now you need to create the Cloud Function, the following HCL snippet demonstrates this:

The event_trigger block in particular specifies which GCS bucket to watch and what events will trigger invocation of the function. Bucket events include:

  • (the creation of a new object)

You could add additional logic to the Cloud Function code to look for specific object names or naming patterns, but keep in mind the function will fire upon every event matching the event_type and resource criteria.

To deploy the function, you would simply run:

terraform apply -var="slack_webhook_url="

Now once you upload a file named test-object.txt, voilà!:

Slack notification for a new object created

Full source code is available at: