Implementing GCP Organization Policy Constraints

Implementing GCP Organization Policy Constraints

Overview

The GCP Organization Policy Service provides centralized and programmatic control over cloud resources. Organization policies configure constraints that restrict one or more Google Cloud services, enforced at organization, folder, or project levels. They improve security by blocking external IPs, requiring encryption, and minimizing unauthorized access. Changes can take up to 15 minutes to propagate.

Prerequisites

• GCP Organization with Organization Administrator role
• gcloud CLI configured and authenticated
• Terraform or gcloud for policy management
• Organization Policy Administrator IAM role (roles/orgpolicy.policyAdmin)

Core Concepts

Constraint Types

1. List Constraints: Allow or deny specific values (e.g., allowed regions)
2. Boolean Constraints: Enable or disable a capability (e.g., disable serial port access)
3. Custom Constraints: User-defined rules targeting specific resource fields (Preview)

Policy Inheritance

Policies inherit from the lowest ancestor with an enforced policy. If no ancestor has a policy, Google's managed default behavior applies.

Essential Security Constraints

Restrict VM External IP Addresses

# Deny external IP addresses on all VMs
gcloud resource-manager org-policies set-policy \
  --organization=ORGANIZATION_ID \
  policy.yaml

policy.yaml:

constraint: constraints/compute.vmExternalIpAccess
listPolicy:
  allValues: DENY

Restrict Resource Locations

gcloud org-policies set-policy \
  --organization=ORGANIZATION_ID \
  location-policy.yaml

location-policy.yaml:

constraint: constraints/gcp.resourceLocations
listPolicy:
  allowedValues:
    - "in:us-locations"
    - "in:eu-locations"

Disable Default Service Account Creation

constraint: constraints/iam.automaticIamGrantsForDefaultServiceAccounts
booleanPolicy:
  enforced: true

Require OS Login for SSH

constraint: constraints/compute.requireOsLogin
booleanPolicy:
  enforced: true

Disable Serial Port Access

constraint: constraints/compute.disableSerialPortAccess
booleanPolicy:
  enforced: true

Enforce Uniform Bucket-Level Access

constraint: constraints/storage.uniformBucketLevelAccess
booleanPolicy:
  enforced: true

Restrict Public IP on Cloud SQL

constraint: constraints/sql.restrictPublicIp
booleanPolicy:
  enforced: true

Disable Service Account Key Creation

constraint: constraints/iam.disableServiceAccountKeyCreation
booleanPolicy:
  enforced: true

Terraform Implementation

resource "google_organization_policy" "restrict_vm_external_ip" {
  org_id     = var.org_id
  constraint = "constraints/compute.vmExternalIpAccess"

  list_policy {
    deny {
      all = true
    }
  }
}

resource "google_organization_policy" "restrict_locations" {
  org_id     = var.org_id
  constraint = "constraints/gcp.resourceLocations"

  list_policy {
    allow {
      values = ["in:us-locations", "in:eu-locations"]
    }
  }
}

resource "google_organization_policy" "require_os_login" {
  org_id     = var.org_id
  constraint = "constraints/compute.requireOsLogin"

  boolean_policy {
    enforced = true
  }
}

resource "google_folder_organization_policy" "dev_folder_external_ip" {
  folder     = google_folder.dev.name
  constraint = "constraints/compute.vmExternalIpAccess"

  list_policy {
    allow {
      values = ["projects/dev-project/zones/us-central1-a/instances/bastion-host"]
    }
  }
}

Dry-Run Testing

Use Policy Intelligence tools to test changes before enforcement:

# Create a dry-run policy to monitor impact
gcloud org-policies set-policy \
  --organization=ORGANIZATION_ID \
  dry-run-policy.yaml

dry-run-policy.yaml:

constraint: constraints/compute.vmExternalIpAccess
listPolicy:
  allValues: DENY
dryRunSpec: true

# Check violations against dry-run policy
gcloud org-policies list-custom-constraints \
  --organization=ORGANIZATION_ID

Custom Constraints

# custom-constraint.yaml
name: organizations/ORGANIZATION_ID/customConstraints/custom.disableGKEAutoUpgrade
resourceTypes:
  - container.googleapis.com/NodePool
methodTypes:
  - CREATE
  - UPDATE
condition: "resource.management.autoUpgrade == true"
actionType: DENY
displayName: Deny GKE auto-upgrade on node pools
description: Prevents enabling auto-upgrade on GKE node pools for controlled upgrades

gcloud org-policies set-custom-constraint custom-constraint.yaml

Monitoring and Compliance

List active policies

gcloud org-policies list --organization=ORGANIZATION_ID

Describe a specific policy

gcloud org-policies describe constraints/compute.vmExternalIpAccess \
  --organization=ORGANIZATION_ID

Audit policy violations with Cloud Asset Inventory

gcloud asset search-all-resources \
  --scope=organizations/ORGANIZATION_ID \
  --query="policy:constraints/compute.vmExternalIpAccess"

Recommended Baseline Policies

References

• GCP Organization Policy Constraints: https://docs.google.com/resource-manager/docs/organization-policy/org-policy-constraints
• GCP Policy Intelligence: https://cloud.google.com/policy-intelligence
• CIS GCP Foundations Benchmark