# Trigger Workflows using Pub/Sub messages (gcloud CLI)
This quickstart shows you how to execute a workflow using an
[Eventarc trigger](https://docs.cloud.google.com/eventarc/docs/workflows/route-trigger-cloud-pubsub) that receives
events using Pub/Sub. The trigger executes the workflow by passing
events delivered through Pub/Sub as
[runtime arguments](https://docs.cloud.google.com/workflows/docs/passing-runtime-arguments.md.txt)
to a destination workflow.
In this quickstart, you will:
1. Use Workflows to create and deploy a workflow that decodes and returns Pub/Sub messages.
2. Create an Eventarc trigger that connects a Pub/Sub topic to a Workflows event receiver.
3. Publish a message to the Pub/Sub topic to generate an event. This event is passed as a runtime argument to the destination workflow.
4. View the Pub/Sub message as a result of the workflow execution.
## Before you begin
Make sure that you have access to this feature by [requesting to have your
project added](https://docs.google.com/forms/d/e/1FAIpQLSdgwrSV8Y4xZv_tvI6X2JEGX1-ty9yizv3_EAOVHWVKXvDLEA/viewform)
to private previews for Google Cloud Workflows.
1. Update gcloud components:
```bash
gcloud components update
```
2. Enable the Compute Engine, Eventarc, Pub/Sub, and Workflows APIs.
```bash
gcloud services enable \
compute.googleapis.com \
eventarc.googleapis.com \
pubsub.googleapis.com \
workflows.googleapis.com \
workflowexecutions.googleapis.com
```
3. Set the configuration variables used in this tutorial:
```bash
export WORKFLOW_LOCATION=us-central1
export TRIGGER_LOCATION=us-central1
export PROJECT_ID=PROJECT_ID
gcloud config set project ${PROJECT_ID}
gcloud config set workflows/location ${WORKFLOW_LOCATION}
gcloud config set eventarc/location ${TRIGGER_LOCATION}
```
4. If you are the project creator, you are granted the
[basic Owner role](https://docs.cloud.google.com/iam/docs/roles-overview.md.txt#basic)
(`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](https://docs.cloud.google.com/eventarc/docs/all-roles-permissions.md.txt) 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](https://docs.cloud.google.com/iam/docs/roles-permissions/eventarc.md.txt#eventarc.admin) (`roles/eventarc.admin`)
- [Logs View Accessor](https://docs.cloud.google.com/iam/docs/roles-permissions/logging.md.txt#logging.viewAccessor) (`roles/logging.viewAccessor`)
- [Project IAM Admin](https://docs.cloud.google.com/iam/docs/roles-permissions/resourcemanager.md.txt#resourcemanager.projectIamAdmin) (`roles/resourcemanager.projectIamAdmin`)
- [Pub/Sub Publisher](https://docs.cloud.google.com/iam/docs/roles-permissions/pubsub.md.txt#pubsub.publisher) (`roles/pubsub.publisher`)
- [Service Account Admin](https://docs.cloud.google.com/iam/docs/roles-permissions/iam.md.txt#iam.serviceAccountAdmin) (`roles/iam.serviceAccountAdmin`)
- [Service Account User](https://docs.cloud.google.com/iam/docs/roles-permissions/iam.md.txt#iam.serviceAccountUser) (`roles/iam.serviceAccountUser`)
- [Service Usage Admin](https://docs.cloud.google.com/iam/docs/roles-permissions/serviceusage.md.txt#serviceusage.serviceUsageAdmin) (`roles/serviceusage.serviceUsageAdmin`)
- [Workflows Admin](https://docs.cloud.google.com/iam/docs/roles-permissions/workflows.md.txt#workflows.admin) (`roles/workflows.admin`)
For more information about granting roles, see [Manage access to projects, folders, and organizations](https://docs.cloud.google.com/iam/docs/granting-changing-revoking-access.md.txt).
You might also be able to get
the required permissions through [custom
roles](https://docs.cloud.google.com/iam/docs/creating-custom-roles) or other [predefined
roles](https://docs.cloud.google.com/iam/docs/roles-overview#predefined).
5. Make note of the [Compute Engine
default service account](https://docs.cloud.google.com/iam/docs/service-account-types#default) as you will 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:
```bash
PROJECT_NUMBER-compute@developer.gserviceaccount.com
```
Replace `PROJECT_NUMBER` with your Google Cloud
project number. You can find your project number on the
[Welcome](https://console.cloud.google.com/welcome)
page of the Google Cloud console or by running the following command:
```bash
gcloud projects describe PROJECT_ID --format='value(projectNumber)'
```
For production environments, we strongly recommend
[creating a new service account](https://docs.cloud.google.com/iam/docs/service-accounts-create.md.txt)
and granting it one or more IAM roles that contain the
[minimum permissions required](https://docs.cloud.google.com/iam/docs/best-practices-service-accounts.md.txt#limit-service-account-privileges)
and follow the principle of [least privilege](https://docs.cloud.google.com/iam/docs/using-iam-securely.md.txt#least_privilege).
> [!NOTE]
> **Note:**
>
>
> The [`iam.automaticIamGrantsForDefaultServiceAccounts` organization policy constraint](https://docs.cloud.google.com/resource-manager/docs/organization-policy/restricting-service-accounts#disable_service_account_default_grants)
> 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](https://docs.cloud.google.com/iam/docs/granting-changing-revoking-access.md.txt)
> 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](https://docs.cloud.google.com/policy-intelligence/docs/simulate-iam-policies.md.txt) to see the impact of
> the change, and then [grant and revoke the
> appropriate roles](https://docs.cloud.google.com/iam/docs/granting-changing-revoking-access).
6. Grant the [Workflows
Invoker role](https://docs.cloud.google.com/iam/docs/roles-permissions/workflows#workflows.invoker) (`roles/workflows.invoker`) on the project to the Compute Engine default service account so that the account has permission to trigger your workflow execution.
```bash
gcloud projects add-iam-policy-binding PROJECT_ID \
--member=serviceAccount:PROJECT_NUMBER-compute@developer.gserviceaccount.com \
--role=roles/workflows.invoker
```
7. 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](https://docs.cloud.google.com/iam/docs/roles-permissions/iam#iam.serviceAccountTokenCreator) (`roles/iam.serviceAccountTokenCreator`) to the service agent. Otherwise, this role is granted by default:
```bash
gcloud projects add-iam-policy-binding PROJECT_ID \
--member=serviceAccount:service-PROJECT_NUMBER@gcp-sa-pubsub.iam.gserviceaccount.com \
--role=roles/iam.serviceAccountTokenCreator
```
## Create and deploy a workflow
Create and deploy a workflow that gets executed when a message published to
a Pub/Sub topic triggers a workflow with an HTTP request.
1. Open a terminal or [Cloud Shell](https://console.cloud.google.com/welcome?cloudshell=true).
2. In your home directory, create a new file called `myFirstWorkflow.yaml` or `myFirstWorkflow.json`.
3. Copy and paste the following into the new file and save it:
### YAML
```yaml
main:
params: [event]
steps:
- decode_pubsub_message:
assign:
- base64: ${base64.decode(event.data.message.data)}
- message: ${text.decode(base64)}
- return_pubsub_message:
return: ${message}
```
### JSON
```json
{
"main": {
"params": [
"event"
],
"steps": [
{
"decode_pubsub_message": {
"assign": [
{
"base64": "${base64.decode(event.data.message.data)}"
},
{
"message": "${text.decode(base64)}"
}
]
}
},
{
"return_pubsub_message": {
"return": "${message}"
}
}
]
}
}
```
4. Deploy the workflow:
```bash
export MY_WORKFLOW=myFirstWorkflow
gcloud workflows deploy ${MY_WORKFLOW} --source=myFirstWorkflow.yaml
```
Replace `.yaml` with `.json` if you copied the JSON version of the example workflow.
## Create an Eventarc trigger
When a message is published to the Pub/Sub topic, the event
triggers the workflow.
1. Create a trigger to listen for Pub/Sub messages:
### New Pub/Sub topic
```yaml
gcloud eventarc triggers create events-pubsub-trigger \
--destination-workflow=${MY_WORKFLOW} \
--destination-workflow-location=${WORKFLOW_LOCATION} \
--event-filters="type=google.cloud.pubsub.topic.v1.messagePublished" \
--service-account="PROJECT_NUMBER-compute@developer.gserviceaccount.com"
```
This creates a new Pub/Sub topic and a trigger for it
called `events-pubsub-trigger`.
### Existing Pub/Sub topic
```json
gcloud eventarc triggers create events-pubsub-trigger \
--destination-workflow=${MY_WORKFLOW} \
--destination-workflow-location=${WORKFLOW_LOCATION} \
--event-filters="type=google.cloud.pubsub.topic.v1.messagePublished" \
--service-account="PROJECT_NUMBER-compute@developer.gserviceaccount.com" \
--transport-topic=TOPIC_ID
```
Replace `TOPIC_ID` with the ID of the existing
Pub/Sub topic.
This creates a trigger called `events-pubsub-trigger` for an existing
Pub/Sub topic.
**Note:** By default, Pub/Sub subscriptions created for Eventarc persist regardless of activity and don't expire. To change the inactivity duration, see [Subscription properties](https://docs.cloud.google.com/pubsub/docs/subscription-properties.md.txt).
Note that when creating an Eventarc trigger for the first
time in a Google Cloud project, there might be a delay in provisioning
the Eventarc service agent. This issue can usually be resolved
by attempting to create the trigger again. For more information, see
[Permission denied errors](https://docs.cloud.google.com/eventarc/docs/troubleshooting.md.txt#trigger-error).
2. Confirm that the trigger was successfully created:
```bash
gcloud eventarc triggers describe events-pubsub-trigger --location=${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/events-pubsub-trigger
```
## Generate and view an event
Publish a message to the Pub/Sub topic to generate an event and
trigger the workflow. The generated event is passed as a
[runtime argument](https://docs.cloud.google.com/workflows/docs/passing-runtime-arguments.md.txt) to the
workflow which returns the Pub/Sub message as a result of
the workflow execution. Make sure that the [size of the events](https://docs.cloud.google.com/workflows/quotas.md.txt#resource_limit)
you pass to the workflow does not exceed 512 KB.
1. If you created a trigger for a new Pub/Sub topic, find and
set the Pub/Sub topic created, as an environment
variable:
```bash
export TOPIC_ID=$(basename $(gcloud eventarc triggers describe events-pubsub-trigger --format='value(transport.pubsub.topic)'))
```
2. To trigger the workflow, send a message to the Pub/Sub topic:
```bash
gcloud pubsub topics publish $TOPIC_ID --message "Hello there"
```
The generated event is passed as a runtime argument to the workflow
which returns a "Hello there" message.
3. To verify that a workflows execution was triggered, list the last five
executions:
```bash
gcloud workflows executions list ${MY_WORKFLOW} --limit=5
```
The output should be similar to the following, listing a NAME and STATE equal
to `SUCCEEDED` for each workflow execution:
```
NAME: projects/606789101455/locations/us-central1/workflows/myFirstWorkflow/executions/8c02b8f1-8836-4a6d-99d9-fc321eb9668f
STATE: SUCCEEDED
START_TIME: 2021-09-13T19:15:10.275677049Z
END_TIME: 2021-09-13T19:15:10.963136883Z
NAME: projects/606789101455/locations/us-central1/workflows/myFirstWorkflow/executions/a6319d9d-36a6-4117-904e-3d1118bdc90a
STATE: SUCCEEDED
START_TIME: 2021-09-13T17:28:51.492864252Z
END_TIME: 2021-09-13T17:28:52.227212414Z
```
Note that in the `NAME` field in the preceding example,
`a6319d9d-36a6-4117-904e-3d1118bdc90a` is the ID of the workflow execution.
Copy your execution ID to use in the next step.
4. To view the execution status, run the following command:
```bash
gcloud workflows executions describe WORKFLOW_EXECUTION_ID --workflow=${MY_WORKFLOW}
```
Replace `WORKFLOW_EXECUTION_ID` with the ID of the
workflow execution that corresponds to the publishing time of the
Pub/Sub topic. The output is similar to the following:
```
argument: [...]
endTime: '2021-09-13T17:28:47.301012152Z'
name: projects/1234567/locations/us-central1/workflows/myFirstWorkflow/executions/f72bc6d4-5ea0-4dfb-bb14-2dae82303120
result: 'Hello there'
startTime: '2021-09-13T17:28:51.492864252Z'
state: SUCCEEDED
```
5. Verify that the `publish_time` at which the Pub/Sub message
was published and the `startTime` of the workflow execution correspond to
each other.
Congratulations, you have successfully generated an event using a
Pub/Sub topic that has triggered a Workflows
event receiver using Eventarc.
## Clean up
1. Delete the workflow you created:
```bash
gcloud workflows delete ${MY_WORKFLOW}
```
When asked if you want to continue, enter `y`.
2. Delete the trigger you created:
```bash
gcloud eventarc triggers delete events-pubsub-trigger
```
3. 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]
> **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
```
## What's next
- [Control the order of execution in a workflow](https://docs.cloud.google.com/workflows/docs/controlling-execution-order.md.txt)
- [Create a trigger to route Pub/Sub events to Workflows](https://docs.cloud.google.com/eventarc/standard/docs/workflows/route-trigger-cloud-pubsub.md.txt)