Google Pub/Sub PERMISSION_DENIED error encountered when accessing Google Pub/Sub resources.

The client does not have permission to access the requested resource.

Understanding Google Pub/Sub

Google Cloud Pub/Sub is a messaging service for exchanging event data among applications and services. It allows you to send and receive messages between independent applications, ensuring reliable communication and data flow.

Identifying the Symptom

When working with Google Pub/Sub, you might encounter the PERMISSION_DENIED error. This error typically occurs when a client attempts to access a Pub/Sub resource without the necessary permissions.

What You Observe

When this error occurs, you will see a message similar to:

{
"error": {
"code": 403,
"message": "PERMISSION_DENIED",
"status": "PERMISSION_DENIED"
}
}

Explaining the Issue

The PERMISSION_DENIED error indicates that the client does not have the required permissions to perform the requested operation on a Pub/Sub resource. This is often due to missing or incorrect Identity and Access Management (IAM) roles.

Common Causes

  • The service account or user lacks the necessary IAM roles.
  • IAM policies are not correctly configured.
  • The resource being accessed does not exist or is incorrectly specified.

Steps to Fix the Issue

To resolve the PERMISSION_DENIED error, follow these steps:

Step 1: Verify IAM Roles

Ensure that the service account or user has the appropriate IAM roles. For publishing messages, the pubsub.publisher role is required. For subscribing to messages, the pubsub.subscriber role is necessary.

gcloud projects get-iam-policy [PROJECT_ID] --flatten="bindings[].members" --format='table(bindings.role)' --filter="bindings.members:[YOUR_SERVICE_ACCOUNT]"

Replace [PROJECT_ID] with your project ID and [YOUR_SERVICE_ACCOUNT] with your service account email.

Step 2: Assign Missing Roles

If roles are missing, assign them using the following command:

gcloud projects add-iam-policy-binding [PROJECT_ID] \
--member="serviceAccount:[YOUR_SERVICE_ACCOUNT]" \
--role="roles/pubsub.publisher"

Repeat for the pubsub.subscriber role if needed.

Step 3: Check Resource Existence

Ensure that the resource you are trying to access exists and is correctly specified in your request. Use the Google Cloud Console or the Pub/Sub REST API to verify resource details.

Additional Resources

For more information on managing IAM roles, refer to the Google Cloud IAM documentation. To learn more about Pub/Sub, visit the Google Cloud Pub/Sub Overview.

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