Manage VPC firewall rule resources by using custom constraints

Google Cloud Organization Policy gives you centralized, programmatic control over your organization's resources. As the organization policy administrator, you can define an organization policy, which is a set of restrictions called constraints that apply to Google Cloud resources and descendants of those resources in the Google Cloud resource hierarchy. You can enforce organization policies at the organization, folder, or project level.

Organization Policy provides predefined constraints for various Google Cloud services. However, if you want more granular, customizable control over the specific fields that are restricted in your organization policies, you can also create custom constraints and enforce those custom constraints in a custom organization policy.

Policy inheritance

By default, organization policies are inherited by the descendants of the resources on which you enforce the policy. For example, if you enforce a policy on a folder, Google Cloud enforces the policy on all projects in the folder. To learn more about this behavior and how to change it, see Hierarchy evaluation rules.

Cloud NGFW supported resources

For VPC firewall rules, you can set custom constraints on the following resources and fields.

• Firewall: compute.googleapis.com/Firewall
  • Name: resource.name
  • Description: resource.description
  • Network: resource.network
  • Priority: resource.priority
  • Source ranges: resource.sourceRanges[]
  • Destination ranges: resource.destinationRanges[]
  • Source tags: resource.sourceTags[]
  • Target tags: resource.targetTags[]
  • Allow rules: resource.allowed[]
    • Protocol: resource.allowed[].IPProtocol
    • Ports: resource.allowed[].ports[]
  • Deny rules: resource.denied[]
    • Protocol: resource.denied[].IPProtocol
    • Ports: resource.denied[].ports[]
  • Direction: resource.direction
  • Is disabled: resource.disabled

Note: To create custom constraints based on protocols or ports, we recommend that you use the custom CEL function containsFirewallPort. For more information, see Defining custom constraints.

Defining custom constraints

A custom constraint is defined by the resources, methods, conditions, and actions that are supported by the service on which you are enforcing the organization policy. Conditions for your custom constraints are defined using Common Expression Language (CEL). For more information about how to build conditions in custom constraints using CEL, see the CEL section of Creating and managing organization policies.

In addition to the standard CEL functions, you can use the custom CEL function containsFirewallPort to create custom constraints for firewall rules. You can use this function to create a constraint that refers to a particular protocol, or a protocol and port combination.

• Protocol only: resource.allowed.containsFirewallPort('PROTOCOL')
• Protocol and port: resource.allowed.containsFirewallPort('PROTOCOL', 'PORT_NUMBER')

For information about allowed protocols, see Protocols and ports.

Before you begin

• If you haven't already, then set up authentication. Authentication is the process by which your identity is verified for access to Google Cloud services and APIs. To run code or samples from a local development environment, you can authenticate to Compute Engine by selecting one of the following options:
  

  Select the tab for how you plan to use the samples on this page:

  Console

  When you use the Google Cloud console to access Google Cloud services and APIs, you don't need to set up authentication.

  gcloud

  1. Install the Google Cloud CLI, then initialize it by running the following command:

     gcloud init

     Note: If you installed the gcloud CLI previously, make sure you have the latest version by running gcloud components update.
  2. Set a default region and zone.

  REST

  To use the REST API samples on this page in a local development environment, you use the credentials you provide to the gcloud CLI.

  Install the Google Cloud CLI, then initialize it by running the following command:

  gcloud init

  For more information, see Authenticate for using REST in the Google Cloud authentication documentation.

* Ensure that you know your organization ID.

Required roles

To get the permissions that you need to manage organization policies for Cloud Next Generation Firewall resources, ask your administrator to grant you the following IAM roles:

• Organization policy administrator (roles/orgpolicy.policyAdmin) on the organization resource
• To test the constraints:
  • Compute Network Admin (roles/compute.networkAdmin) on the project
  • Service Account User (roles/iam.serviceAccountUser) on the project

For more information about granting roles, see Manage access to projects, folders, and organizations.

These predefined roles contain the permissions required to manage organization policies for Cloud Next Generation Firewall resources. To see the exact permissions that are required, expand the Required permissions section:

Required permissions

The following permissions are required to manage organization policies for Cloud Next Generation Firewall resources:

• orgpolicy.constraints.list
• orgpolicy.policies.create
• orgpolicy.policies.delete
• orgpolicy.policies.list
• orgpolicy.policies.update
• orgpolicy.policy.get
• orgpolicy.policy.set

You might also be able to get these permissions with custom roles or other predefined roles.

Set up a custom constraint

You can create a custom constraint and set it up for use in organization policies by using the Google Cloud console or Google Cloud CLI.

Console

1. In the Google Cloud console, go to the Organization policies page.

   Go to Organization policies

2. Select the Project picker at the top of the page.

3. From the Project picker, select the resource for which you want to set the organization policy.

4. Click Custom constraint.

5. In the Display name box, enter a human-friendly name for the constraint. This field has a maximum length of 200 characters. Don't use PII or sensitive data in constraint names, because they could be exposed in error messages.

6. In the Constraint ID box, enter the name you want for your new custom constraint. A custom constraint must start with custom., and can only include uppercase letters, lowercase letters, or numbers, for example, custom.httpFirewallRule. The maximum length of this field is 70 characters, not counting the prefix, for example, organizations/123456789/customConstraints/custom..

7. In the Description box, enter a human-friendly description of the constraint to display as an error message when the policy is violated. This field has a maximum length of 2,000 characters.

8. In the Resource type box, select the name of the Google Cloud REST resource containing the object and field you want to restrict. For example, compute.googleapis.com/Firewall.

9. Under Enforcement method, select whether to enforce the constraint on the REST CREATE method only or on both the REST CREATE and UPDATE methods.

10. To define a condition, click Edit condition.

    1. In the Add condition panel, create a CEL condition that refers to a supported service resource. This field has a maximum length of 1,000 characters.

    2. Click Save.

11. Under Action, select whether to allow or deny the evaluated method if the above condition is met.

12. Click Create constraint.

When you have entered a value into each field, the equivalent YAML configuration for this custom constraint appears on the right.

gcloud

To create a custom constraint using the Google Cloud CLI, create a YAML file.

name: organizations/ORGANIZATION_ID/customConstraints/CONSTRAINT_NAME
resource_types: compute.googleapis.com/RESOURCE_NAME
method_types:
– METHOD1
– METHOD2
condition: "CONDITION"
action_type: ACTION
display_name: DISPLAY_NAME
description: DESCRIPTION

Replace the following:

• ORGANIZATION_ID: your organization ID, such as 123456789.

• CONSTRAINT_NAME: the name you want for your new custom constraint. A custom constraint must start with custom., and can only include uppercase letters, lowercase letters, or numbers, for example, custom.httpFirewallRule. The maximum length of this field is 70 characters, not counting the prefix, for example, organizations/123456789/customConstraints/custom.

• RESOURCE_NAME: the name (not the URI) of the Compute Engine API REST resource containing the object and field you want to restrict. For example, Firewall.

• METHOD1,METHOD2,...: a list of RESTful methods for which to enforce the constraint. Can be CREATE or CREATE and UPDATE.

• CONDITION: a CEL condition that is written against a representation of a supported service resource. This field has a maximum length of 1,000 characters. See Supported resources for more information about the resources available to write conditions against.

• ACTION: the action to take if the condition is met. This can be either ALLOW or DENY.

• DISPLAY_NAME: a human-friendly name for the constraint. This field has a maximum length of 200 characters.

• DESCRIPTION: a human-friendly description of the constraint to display as an error message when the policy is violated. This field has a maximum length of 2,000 characters.

For more information about how to create a custom constraint, see Defining custom constraints.

After you have created the YAML file for a new custom constraint, you must set it up to make it available for organization policies in your organization. To set up a custom constraint, use the gcloud org-policies set-custom-constraint command:

gcloud org-policies set-custom-constraint CONSTRAINT_PATH

Replace CONSTRAINT_PATH with the full path to your custom constraint file. For example, /home/user/customconstraint.yaml. Once completed, your custom constraints are available as organization policies in your list of Google Cloud organization policies. To verify that the custom constraint exists, use the gcloud org-policies list-custom-constraints command:

gcloud org-policies list-custom-constraints --organization=ORGANIZATION_ID

Replace ORGANIZATION_ID with the ID of your organization resource. For more information, see Viewing organization policies.

Enforce a custom constraint

You can enforce a boolean constraint by creating an organization policy that references it, and then applying that organization policy to a Google Cloud resource.

Console

1. In the Google Cloud console, go to the Organization policies page.

   Go to Organization policies

2. From the project picker, select the project for which you want to set the organization policy.
3. From the list on the Organization policies page, select your constraint to view the Policy details page for that constraint.
4. To configure the organization policy for this resource, click Manage policy.
5. On the Edit policy page, select Override parent's policy.
6. Click Add a rule.
7. In the Enforcement section, select whether enforcement of this organization policy is on or off.
8. Optional: To make the organization policy conditional on a tag, click Add condition. Note that if you add a conditional rule to an organization policy, you must add at least one unconditional rule or the policy cannot be saved. For more information, see Setting an organization policy with tags.
9. If this is a custom constraint, you can click Test changes to simulate the effect of this organization policy. For more information, see Test organization policy changes with Policy Simulator.
10. To finish and apply the organization policy, click Set policy. The policy requires up to 15 minutes to take effect.

gcloud

To create an organization policy that enforces a boolean constraint, create a policy YAML file that references the constraint:

      name: projects/PROJECT_ID/policies/CONSTRAINT_NAME
      spec:
        rules:
        - enforce: true
    

Replace the following:

• PROJECT_ID: the project on which you want to enforce your constraint.
• CONSTRAINT_NAME: the name you defined for your custom constraint. For example, custom.httpFirewallRule.

To enforce the organization policy containing the constraint, run the following command:

    gcloud org-policies set-policy POLICY_PATH
    

Replace POLICY_PATH with the full path to your organization policy YAML file. The policy requires up to 15 minutes to take effect.

Example: Create a constraint that restricts creating firewall rules that allow SSH connections

This constraint prevents the creation of ingress firewall rules that allow SSH connections from any IP address range other than the following ranges:

• 10.0.0.0/8: an internal IP address range used in the VPC network.
• 192.168.0.0/16: an internal IP address range used in the VPC network.

• 35.235.240.0/20: the IP address range used by Identity-Aware Proxy (IAP) for TCP forwarding.

gcloud

1. Create a restrictSshRanges.yaml constraint file with the following information.

   name: organizations/ORGANIZATION_ID/customConstraints/custom.restrictSshRanges
   resource_types: compute.googleapis.com/Firewall
   condition: "resource.direction.matches('INGRESS') && resource.allowed.containsFirewallPort('tcp', '22') && !resource.sourceRanges.all(range, range == '35.235.240.0/20' || range.startsWith('10.') || range.startsWith('192.168.'))"
   action_type: DENY
   method_types: CREATE
   display_name: Limit firewall rules that allow ingress SSH traffic
   description: Firewall rules that allow ingress SSH traffic can only be created with allowed source ranges.
   

   Replace ORGANIZATION_ID with your organization ID.

2. Set the custom constraint.

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

3. Create a restrictSshRanges-policy.yaml policy file with the information provided in the following example and enforce the constraint at the project level. You can also set this constraint at the organization or folder level.

       name: projects/PROJECT_ID/policies/custom.restrictSshRanges
       spec:
         rules:
         – enforce: true
   

   Replace PROJECT_ID with your project ID.

4. Enforce the policy.

   gcloud org-policies set-policy restrictSshRanges-policy.yaml
   

5. To test the constraint, create an auto mode VPC network.

   gcloud compute firewall-rules create ssh-firewall-rule \
       --action=ALLOW  --direction=INGRESS  --network=NETWORK \
       --priority=1000  --rules=tcp:22  --source-ranges=0.0.0.0/0
   

   Replace NETWORK with your network name. The output is similar to the following:

   ERROR: (gcloud.compute.networks.create) Could not fetch resource:
   - Operation denied by custom org policy: [customConstraints/custom.restrictSshRanges] : Firewall rules that allow ingress SSH traffic can only be created with allowed source ranges.
   

Pricing

The Organization Policy Service, including predefined and custom organization policies, is offered at no charge.

What's next

• Introduction to the Organization Policy Service
• Create and manage organization policies
• Organization policy constraints