Multiple Knative Brokers in different namespaces that connect and use a single RabbitMQ cluster instance

[xtreme-sameer-vohra]

Problem
A user might prefer to create a single RabbitMQ cluster with sufficient capacity to service all messaging needs of a single K8s cluster. It would be desirable to have multiple Knative Brokers (across multiple namespaces such as foo, bar) connect to and use a single RabbitMQ cluster thats created in baz namespace.

Persona:
Which persona is this feature for?
This feature would be used by the K8s Cluster Administrator

Exit Criteria
Be able to setup something like

1. Install RabbitMQ operators and eventing-rabbitmq
2. Create RabbitMQ Cluster my-rabbit-cluster in namespace baz
3. Create a Knative Broker foo-broker (backed by my-rabbit-cluster) in namespace foo
4. Create a Knative Broker bar-broker (backed by my-rabbit-cluster) in namespace bar
5. Ensure the status of both Brokers is true
6. Ensure that an event producer (eg. PingSource) can send events to the brokers and an event consumer (eg. event-display) can consume events from the two brokers.

[gvmw]

This feature was introduced in the messaging topology operator in rabbitmq/messaging-topology-operator#201. It was documented via rabbitmq/rabbitmq-website#1264, and the latest public version is here: https://www.rabbitmq.com/kubernetes/operator/using-topology-operator.html#namespace-scope

The fix appears simple: we just need to annotate the RabbitmqCluster object with rabbitmq.com/topology-allowed-namespaces: "*". Trying it out now, then will update all places that mention the topology operator.

[gvmw]

There is another part to this. When the Exchange object gets created, it should pick up the Broker namespace property.

Given the following Broker object:

apiVersion: eventing.knative.dev/v1
kind: Broker
metadata:
  name: cloudevents-player-rabbitmq
  namespace: cloudevents-player
  annotations:
    eventing.knative.dev/broker.class: RabbitMQBroker
spec:
  config:
    apiVersion: rabbitmq.com/v1beta1
    kind: RabbitmqCluster
    name: rabbitmq-knative-eventing
    namespace: knative-eventing

This Exchange object gets created internally:

apiVersion: rabbitmq.com/v1beta1
kind: Exchange
metadata:
  creationTimestamp: "2021-10-14T12:38:02Z"
  generation: 1
  labels:
    eventing.knative.dev/broker: cloudevents-player-rabbitmq
  name: b.cloudevents-player.cloudevent800f452d438e304bcd51cc5b6d8c122f
  namespace: cloudevents-player
  ownerReferences:
  - apiVersion: eventing.knative.dev/v1
    blockOwnerDeletion: true
    controller: true
    kind: Broker
    name: cloudevents-player-rabbitmq
    uid: 48606b0c-66c8-4c27-813e-c667dace1ea0
  resourceVersion: "69707"
  uid: 7ef0e853-779c-4d0b-8078-ee3e0c18e75a
spec:
  durable: true
  name: b.cloudevents-player.cloudevent800f452d438e304bcd51cc5b6d8c122f
  rabbitmqClusterReference:
    name: rabbitmq-knative-eventing
  type: headers
  vhost: /

This is what's wrong:

apiVersion: rabbitmq.com/v1beta1
kind: Exchange
...

spec:
  durable: true
  name: b.cloudevents-player.cloudevent800f452d438e304bcd51cc5b6d8c122f
  rabbitmqClusterReference:
    name: rabbitmq-knative-eventing
+   namespace: knative-eventing

[gvmw]

/assign