Creating resource references

A Google Cloud resource created with Config Connector can reference other resources. Config Connector defines these relationships through resource references. This topic explains how to create resources with references.

Types of references

In Config Connector, references can be dependencies or links.

Dependencies
A dependency reference refers to an existing Google Cloud resource necessary for the Config Connector resource. For example, a firewall rule cannot exist without a network
Links
A link reference ties independent resources together. For example, a Project can be associated with a Billing Account.

Specifying resource references

You specify resource references in the resource's spec. The field's name is the resource's short name followed by Ref. For example:

  • The reference to a PubSubTopic named topic is topicRef.
  • The reference to a StorageBucket named bucket is bucketRef.

The reference is an object with a single field (name). The resource in resourceRef is replaced with the reference's name.

The following YAML file describes a Pub/Sub PubSubSubscription that references a PubSubTopic named myTopic.

apiVersion: pubsub.cnrm.cloud.google.com/v1beta1
kind: PubSubSubscription
metadata:
  name: pubsubsubscription-referencing-topic
spec:
  topicRef:
    name: myTopic

Pub/Sub example

Create a PubSubTopic

In this example, you create a PubSubSubscription that depends on a PubSubTopic.

  1. Copy the following into a file named pubsub-topic.yaml:

    apiVersion: pubsub.cnrm.cloud.google.com/v1beta1
    kind: PubSubTopic
    metadata:
    name: TOPIC_NAME
    

    Replace TOPIC_NAME with your desired PubSubTopic name

    For example, to create a topic named myTopic you could use the following YAML file:

    apiVersion: pubsub.cnrm.cloud.google.com/v1beta1
    kind: PubSubTopic
    metadata:
      name: myTopic
    
  2. Create the PubSubTopic with kubectl apply.

    kubectl --namespace CC_NAMESPACE apply -f pubsub-topic.yaml

    Replace CC_NAMESPACE with the namespace Config Connector manages resources from.

Create a PubSubSubscription

  1. Copy the following into a file named `pubsub-subscription.yaml:

    apiVersion: pubsub.cnrm.cloud.google.com/v1beta1
    kind: PubSubSubscription
    metadata:
      name: pubsubsubscription-referencing-topic
    spec:
      topicRef:
        name: TOPIC_NAME
    

    Replace TOPIC_NAME with the PubSubTopic name you used in step 1. For example, the YAML referencing the topic myTopic you created earlier is:

    apiVersion: pubsub.cnrm.cloud.google.com/v1beta1
    kind: PubSubSubscription
    metadata:
      name: pubsubsubscription-referencing-topic
    spec:
      topicRef:
        name: myTopic
    
  2. Create the PubSubSubscription with kubectl apply.

    kubectl --namespace CC_NAMESPACE apply -f pubsub-subscription.yaml 

    Replace CC_NAMESPACE with the namespace Config Connector manages resources from.

External references

Config Connector can reference resources that it does not manage. These are known as External References. For example, the ComputeURLMap below references a BackendService named test-backendservice.

apiVersion: compute.cnrm.cloud.google.com/v1beta1
kind: ComputeURLMap
metadata:
  name: test-urlmap
spec:
  location: global
  defaultService:
    backendServiceRef:
      external: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendServices/test-backendservice

The format of values accepted by external depends on the resource. Consult the documentation for particular resources in the Resource reference. You can find out what values external accepts by reading the descriptions of the resource's external fields.

External references for IAMPolicy and IAMPolicyMember

IAMPolicy and IAMPolicyMember also supports External References. For example, the IAMPolicyMember below references a Project with the project ID test-project.

apiVersion: iam.cnrm.cloud.google.com/v1beta1
kind: IAMPolicyMember
metadata:
  name: test-iampolicymember
spec:
  member: serviceAccount:test-serviceaccount@test-project.iam.gserviceaccount.com
  role: roles/storage.admin
  resourceRef:
    apiVersion: resourcemanager.cnrm.cloud.google.com/v1beta1
    kind: Project
    external: projects/test-project

You can find out what format the external field accepts by reading the reference documentation. The IAMPolicy and IAMPolicyMember pages list the accepted format for all supported resources. The formats are listed in the "External Reference Formats" column of the Supported Resources table. You can also go to an individual resource's reference page (for example, PubSubTopic) and look at the value listed in the "IAM External Reference Format" row of the resource's summary table.

Cross-namespace references

Config Connector allows resources to reference resources in other namespaces. However, if Config Connector is installed in namespaced-mode, you need to grant Config Connector additional permissions to allow for cross-namespace references.

For example, if you want to create resources in NAMESPACE_A that reference resources in NAMESPACE_B, you need create the following RoleBinding:

apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  namespace: NAMESPACE_B
  name: allow-references-from-NAMESPACE_A
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: cnrm-admin
subjects:
- kind: ServiceAccount
  name: cnrm-controller-manager-NAMESPACE_A
  namespace: cnrm-system

What's next

  • Review the Resource reference to learn about the resources Config Connector supports.

  • See how you can use a resource reference to a Secret in your Config Connector cluster.