Nothing kills productivity faster than hitting an authorization wall when you're just trying to restart your GCP instance. The error message "Error 4033: Reason not-authorized" typically appears when your IAM permissions aren't properly configured, but there are several potential root causes we need to examine.

Before diving deep, let's verify these common scenarios:

gcloud projects get-iam-policy PROJECT_ID --format=json | grep -A 5 "user:your-email@domain.com"

If this returns empty, you definitely have permission issues. But sometimes the problem is more subtle.

In GCP, authorization often fails due to service account impersonation chain breaks. Try this diagnostic command:

gcloud auth list
gcloud config list account
gcloud auth print-access-token

Compare the output with your target project's IAM settings. The account shown needs compute.instances.stop and compute.instances.start permissions at minimum.

If you manage infrastructure with Terraform, permission drift can occur. Here's how to reconcile:

resource "google_project_iam_member" "instance_admin" {
  project = var.project_id
  role    = "roles/compute.instanceAdmin.v1"
  member  = "serviceAccount:${google_service_account.default.email}"
}

Surprisingly, the Compute Engine API might be disabled. Verify with:

gcloud services list --enabled --project=PROJECT_ID | grep compute

If missing, enable it:

gcloud services enable compute.googleapis.com

Enterprise GCP setups often have organization policies blocking instance management. Check constraints:

gcloud resource-manager org-policies list --project=PROJECT_ID

Look for policies like constraints/compute.disableSerialPortAccess that might interfere.

When scripting instance restarts, always handle auth properly:

from google.oauth2 import service_account
from googleapiclient import discovery

credentials = service_account.Credentials.from_service_account_file(
    'service-account.json',
    scopes=['https://www.googleapis.com/auth/compute'])

service = discovery.build('compute', 'v1', credentials=credentials)

• Verify service account exists in correct project
• Confirm required IAM roles are assigned
• Check for relevant organization policies
• Ensure Compute Engine API is enabled
• Validate credentials in automation scripts

---

When managing Google Cloud Platform (GCP) instances, you might encounter Error 4033 during instance restarts with the authorization message "Reason not-authorized". This typically indicates an IAM permissions issue where your current credentials lack necessary privileges.

The error frequently occurs when:

• Using service accounts with insufficient permissions
• Temporary credential expiration during API operations
• Organization policy restrictions
• Project-level permission changes

First verify your current authentication status:

gcloud auth list
gcloud config get-value project

Then check instance-specific permissions:

gcloud compute instances get-iam-policy [INSTANCE_NAME] \
--zone=[ZONE] --format=json

1. Service Account Permission Fix

Ensure your service account has compute.instanceAdmin.v1 role:

gcloud projects add-iam-policy-binding [PROJECT_ID] \
--member="serviceAccount:[SERVICE_ACCOUNT_EMAIL]" \
--role="roles/compute.instanceAdmin.v1"

2. Temporary Workaround Using gcloud

For immediate needs, try manual restart via CLI:

gcloud compute instances reset [INSTANCE_NAME] \
--zone=[ZONE] --project=[PROJECT_ID]

3. Checking Organization Policies

Some constraints might prevent restarts:

gcloud resource-manager org-policies list \
--project=[PROJECT_ID] | grep compute

If basic fixes don't work, check Cloud Audit Logs:

gcloud logging read \
'logName="projects/[PROJECT_ID]/logs/cloudaudit.googleapis.com%2Factivity" \
AND protoPayload.methodName="v1.compute.instances.reset"' \
--limit=5 --format=json

• Implement regular permission audits
• Use Terraform for IAM management
• Set up monitoring for permission changes

Here's how we fixed this in production:

# First identified missing role
gcloud projects get-iam-policy my-project \
--flatten="bindings[].members" \
--filter="bindings.members:service-account@my-project.iam.gserviceaccount.com"

# Then applied the fix
gcloud projects add-iam-policy-binding my-project \
--member="serviceAccount:service-account@my-project.iam.gserviceaccount.com" \
--role="roles/compute.instanceAdmin.v1"

# Verified with dry-run
gcloud compute instances reset my-instance \
--zone=us-central1-a --dry-run