Trigger Workflows with direct events from Cloud Storage (gcloud CLI)

Standard

This quickstart shows you how to execute a workflow using an Eventarc trigger that receives events from Cloud Storage.

The trigger executes the workflow by listening for an object creation event in a Cloud Storage bucket and passes the event as a runtime argument to a destination workflow.

In this quickstart, you:

Create a Cloud Storage bucket as an event source.
Use Workflows to create and deploy a workflow that extracts and returns the name of the storage bucket and the name of an uploaded file.
Create an Eventarc trigger that connects the Cloud Storage bucket to the Workflows event receiver.
Generate an event by uploading a text file to the Cloud Storage bucket. This event is passed as a runtime argument to the destination workflow.
View the name of the bucket and the name of the text file as a result of the workflow execution.

To follow step-by-step guidance for this task directly in the Google Cloud console, click Guide me:

Guide me

Before you begin

Security constraints defined by your organization might prevent you from completing the following steps. For troubleshooting information, see Develop applications in a constrained Google Cloud environment.

Sign in to your Google Cloud account. If you're new to Google Cloud, create an account to evaluate how our products perform in real-world scenarios. New customers also get $300 in free credits to run, test, and deploy workloads.

Install the Google Cloud CLI.

To initialize the gcloud CLI, run the following command:

gcloud init

Create or select a Google Cloud project.

Create a Google Cloud project:
```
gcloud projects create PROJECT_ID
```
Replace PROJECT_ID with a name for the Google Cloud project you are creating.
Select the Google Cloud project that you created:
```
gcloud config set project PROJECT_ID
```
Replace PROJECT_ID with your Google Cloud project name.

Make sure that billing is enabled for your Google Cloud project.

Install the Google Cloud CLI.

To initialize the gcloud CLI, run the following command:

gcloud init

Create or select a Google Cloud project.

Create a Google Cloud project:
```
gcloud projects create PROJECT_ID
```
Replace PROJECT_ID with a name for the Google Cloud project you are creating.
Select the Google Cloud project that you created:
```
gcloud config set project PROJECT_ID
```
Replace PROJECT_ID with your Google Cloud project name.

Make sure that billing is enabled for your Google Cloud project.

Enable the Compute Engine, Eventarc, Pub/Sub, and Workflows APIs.

gcloud services enable \
compute.googleapis.com \
eventarc.googleapis.com \
pubsub.googleapis.com \
workflows.googleapis.com \
workflowexecutions.googleapis.com

Update gcloud components:
```
gcloud components update
```

Set your environment variables

Set the environment variables used in this quickstart.

export PROJECT_ID=PROJECT_ID
export WORKFLOW_LOCATION=us-central1
export TRIGGER_LOCATION=us-central1
gcloud config set project ${PROJECT_ID}
gcloud config set workflows/location ${WORKFLOW_LOCATION}
gcloud config set eventarc/location ${TRIGGER_LOCATION}

You can find your project ID on the Welcome page of the Google Cloud console.

Set up your service accounts

Grant the required permissions to the service accounts used in this quickstart.

If you are the project creator, you are granted the basic Owner role (roles/owner). By default, this Identity and Access Management (IAM) role includes the permissions necessary for full access to most Google Cloud resources and you can skip this step.

If you are not the project creator, required permissions must be granted on the project to the appropriate principal. For example, a principal can be a Google Account (for end users) or a service account (for applications and compute workloads). For more information, see the Roles and permissions page for your event destination.
Required permissions

To get the permissions that you need to complete this quickstart, ask your administrator to grant you the following IAM roles on your project:
- Eventarc Admin (roles/eventarc.admin)
- Logs View Accessor (roles/logging.viewAccessor)
- Project IAM Admin (roles/resourcemanager.projectIamAdmin)
- Service Account Admin (roles/iam.serviceAccountAdmin)
- Service Account User (roles/iam.serviceAccountUser)
- Service Usage Admin (roles/serviceusage.serviceUsageAdmin)
- Storage Admin (roles/storage.admin)
- Workflows Admin (roles/workflows.admin)
For more information about granting roles, see Manage access to projects, folders, and organizations.

You might also be able to get the required permissions through custom roles or other predefined roles.
Make note of the Compute Engine default service account as you will you attach it to an Eventarc trigger to represent the identity of the trigger for testing purposes. This service account is automatically created after enabling or using a Google Cloud service that uses Compute Engine, and with the following email format:
```
PROJECT_NUMBER-compute@developer.gserviceaccount.com
```
Replace PROJECT_NUMBER with your Google Cloud project number. You can find your project number on the Welcome page of the Google Cloud console or by running the following command:
```
gcloud projects describe PROJECT_ID --format='value(projectNumber)'
```
For production environments, we strongly recommend creating a new service account and granting it one or more IAM roles that contain the minimum permissions required and follow the principle of least privilege.

Note:
The iam.automaticIamGrantsForDefaultServiceAccounts organization policy constraint prevents the Editor role from being automatically granted to default service accounts. If you created your organization after May 3, 2024, this constraint is enforced by default.

We strongly recommend that you enforce this constraint to disable the automatic role grant. If you disable the automatic role grant, you must decide which roles to grant to the default service accounts, and then grant these roles yourself.

If the default service account already has the Editor role, we recommend that you replace the Editor role with less permissive roles. To safely modify the service account's roles, use Policy Simulator to see the impact of the change, and then grant and revoke the appropriate roles.
Grant the Eventarc Event Receiver role (roles/eventarc.eventReceiver) on the project to the Compute Engine default service account so that the Eventarc trigger can receive events from event providers.
```
gcloud projects add-iam-policy-binding PROJECT_ID \
    --member=serviceAccount:PROJECT_NUMBER-compute@developer.gserviceaccount.com \
    --role=roles/eventarc.eventReceiver
```
Grant the Workflows Invoker role (roles/workflows.invoker) on the project to the Compute Engine default service account so that the account has permission to trigger your workflow execution.
```
gcloud projects add-iam-policy-binding PROJECT_ID \
    --member=serviceAccount:PROJECT_NUMBER-compute@developer.gserviceaccount.com \
    --role=roles/workflows.invoker
```

Grant the Logging Logs Writer role (roles/logging.logWriter) on the project to the Compute Engine default service account so that the workflow can send logs to Cloud Logging.

gcloud projects add-iam-policy-binding PROJECT_ID \
    --member=serviceAccount:PROJECT_NUMBER-compute@developer.gserviceaccount.com \
    --role=roles/logging.logWriter

Before creating a trigger for direct events from Cloud Storage, grant the Pub/Sub Publisher role (roles/pubsub.publisher) to the Cloud Storage service agent:

SERVICE_ACCOUNT="$(gcloud storage service-agent --project=PROJECT_ID)"

gcloud projects add-iam-policy-binding PROJECT_ID \
    --member="serviceAccount:${SERVICE_ACCOUNT}" \
    --role='roles/pubsub.publisher'

If you enabled the Cloud Pub/Sub service agent on or before April 8, 2021, to support authenticated Pub/Sub push requests, grant the Service Account Token Creator role (roles/iam.serviceAccountTokenCreator) to the service agent. Otherwise, this role is granted by default:
```
gcloud projects add-iam-policy-binding PROJECT_ID \
    --member=serviceAccount:service-PROJECT_NUMBER@gcp-sa-pubsub.iam.gserviceaccount.com \
    --role=roles/iam.serviceAccountTokenCreator
```

Create a Cloud Storage bucket

Create a Cloud Storage bucket to use as the event source:

  gsutil mb -l us-central1 gs://${PROJECT_ID}-bucket/

Create and deploy a workflow

Create and deploy a workflow that is executed when an object created in the Cloud Storage bucket triggers a workflow with an HTTP request.

In your home directory, create a new file called myEventWorkflow.yaml or myEventWorkflow.json.

Copy and paste the following into the new file and save it:

YAML

  main:
    params: [event]
    steps:
        - log_event:
            call: sys.log
            args:
                text: ${event}
                severity: INFO
        - extract_bucket_object:
            assign:
            - bucket: ${event.data.bucket}
            - object: ${event.data.name}
        - return_bucket_object:
                return:
                    bucket: ${bucket}
                    object: ${object}

JSON

{
"main": {
"params": [
  "event"
],
"steps": [
  {
    "log_event": {
      "call": "sys.log",
      "args": {
        "text": "${event}",
        "severity": "INFO"
      }
    }
  },
  {
    "extract_bucket_object": {
      "assign": [
        {
          "bucket": "${event.data.bucket}"
        },
        {
          "object": "${event.data.name}"
        }
      ]
    }
  },
  {
    "return_bucket_object": {
      "return": {
        "bucket": "${bucket}",
        "object": "${object}"
      }
    }
  }
]
}
}

Deploy the workflow:

export MY_WORKFLOW=myEventWorkflow
gcloud workflows deploy ${MY_WORKFLOW} --source=myEventWorkflow.yaml

Replace .yaml with .json if you copied the JSON version of the example workflow.

Create an Eventarc trigger

The Eventarc trigger sends events from the Cloud Storage bucket to the Workflows destination.

Create a trigger that filters Cloud Storage events:
```
gcloud eventarc triggers create storage-events-trigger \
    --destination-workflow=${MY_WORKFLOW} \
    --event-filters="type=google.cloud.storage.object.v1.finalized" \
    --event-filters="bucket=${PROJECT_ID}-bucket" \
    --service-account="PROJECT_NUMBER-compute@developer.gserviceaccount.com"
```
This creates a trigger called storage-events-trigger.

Note that when creating an Eventarc trigger for the first time in a Google Cloud project, there might be a delay in provisioning the Eventarc service agent. This issue can usually be resolved by attempting to create the trigger again. For more information, see Permission denied errors.

To confirm storage-events-trigger was successfully created, run:

gcloud eventarc triggers describe storage-events-trigger --location=${TRIGGER_LOCATION}

The output should be similar to the following listing the time of creation and trigger location:

createTime: '2021-10-14T15:15:43.872360951Z'
[...]
name: projects/PROJECT_ID/locations/us-central1/triggers/storage-events-trigger

Generate and view an event

To generate an event, upload a text file to Cloud Storage:
```
echo "Hello World" > random.txt
gsutil cp random.txt gs://${PROJECT_ID}-bucket/random.txt
```
The upload generates an event that is passed as a runtime argument to the workflow which returns the names of the storage bucket and uploaded file.

To verify that a workflows execution was triggered, list the last five executions:

gcloud workflows executions list ${MY_WORKFLOW} --limit=5

The output should be similar to the following, listing a NAME and STATE equal to SUCCEEDED for each workflow execution:

NAME: projects/606789101455/locations/us-central1/workflows/myFirstWorkflow/executions/8c02b8f1-8836-4a6d-99d9-fc321eb9668f
STATE: SUCCEEDED
START_TIME: 2021-10-13T03:38:03.019148617Z
END_TIME: 2021-10-13T03:38:03.249705805Z
NAME: projects/606789101455/locations/us-central1/workflows/myFirstWorkflow/executions/a6319d9d-36a6-4117-904e-3d1118bdc90a
STATE: SUCCEEDED
START_TIME: 2021-10-13T17:28:51.492864252Z
END_TIME: 2021-10-13T17:28:52.227212414Z

Note that in the NAME field in the preceding example, a6319d9d-36a6-4117-904e-3d1118bdc90a is the ID of the workflow execution. Copy your execution ID as it is used in the next step.

To view the execution status, run the following command:

gcloud workflows executions describe WORKFLOW_EXECUTION_ID --workflow=${MY_WORKFLOW}

Replace WORKFLOW_EXECUTION_ID with the ID of the workflow execution that corresponds to the time at which the file was uploaded to the bucket.

The output is similar to the following:

argument: [...]
name: projects/218898424763/locations/us-central1/workflows/myEventWorkflow/executions/86d2567b-0f1e-49b3-8b10-cdac5d0f6239
result: '{"bucket":"PROJECT_ID-bucket","object":"random.txt"}'
startTime: '2021-10-13T03:38:03.019148617Z'
state: SUCCEEDED

Verify that the time,"timeCreated": "2021-10-13T03:38" at which the Cloud Storage bucket was updated and the startTime of the workflow execution correspond to each other.

Congratulations, you have successfully generated a Cloud Storage event that has triggered a Workflows event receiver using Eventarc.

Clean up

To avoid incurring charges to your Google Cloud account for the resources used on this page, delete the Google Cloud project with the resources.

Delete the workflow you created:
```
gcloud workflows delete ${MY_WORKFLOW}
```
When asked if you want to continue, enter y.

Delete your storage bucket:

gsutil rm -r gs://${PROJECT_ID}-bucket/

Delete the trigger created in this tutorial:

gcloud eventarc triggers delete storage-events-trigger

Alternatively, you can delete your Google Cloud project to avoid incurring charges. Deleting your Google Cloud project stops billing for all the resources used within that project.
Caution: Deleting a project has the following effects:
- Everything in the project is deleted. If you used an existing project for the tasks in this document, when you delete it, you also delete any other work you've done in the project.
- Custom project IDs are lost. When you created this project, you might have created a custom project ID that you want to use in the future. To preserve the URLs that use the project ID, such as an appspot.com URL, delete selected resources inside the project instead of deleting the whole project.
Delete a Google Cloud project:
```
gcloud projects delete PROJECT_ID
```