Common Notifications bus interface for services

Add a top level field in OpenStackControlPlaneSpec field that holds a
a RabbitMQ cluster CR name reference to be used for publishing and consuming
of notifications in the managed OpenStack instance.

Allow overriding it in OpenStack services templates.

Note about a special handling expected for an empty value by the services
that will be supporting this interface. It should provide backwards
compatibility during oscp and services CRDs upgrades.

The proposed CRD design is not expandable into supporting additional
messaging backends (provided via direct transport_url secret refs, or
the like). For that, the structure should be used instead of a simple string value.

Assume openstack-operator controller should implement a basic
inheritance mechanism from the top level field to the service template
based on the following rules:

if OSCP.Spec.<service_name>.Template.NotificationsBusInstance == nil
    OSCP.Spec.<service_name>.Template.NotificationsBusInstance = \
        OSCP.Spec.NotificationsBus.RabbitMqClusterName

We leave further handling of empty values for the services specific
implementation.

Assume a similar pattern to be applied later for
KeystoneAPI.Spec.RabbitMqClusterName and other services that need to
consume or publish notifications to keep things consistent across the
board.

Signed-off-by: Bohdan Dobrelia <bdobreli@redhat.com>

Author: bogdando

apis/bases/core.openstack.org_openstackcontrolplanes.yaml

@@ -9498,6 +9498,11 @@ spec:
                 additionalProperties:
                   type: string
                 type: object
+              notificationsBus:
+                properties:
+                  rabbitMqClusterName:
+                    type: string
+                type: object
               nova:
                 properties:
                   apiOverride:

apis/core/v1beta1/openstackcontrolplane_types.go

@@ -126,6 +126,11 @@ type OpenStackControlPlaneSpec struct {
 	// Rabbitmq - Parameters related to the Rabbitmq service
 	Rabbitmq RabbitmqSection `json:"rabbitmq,omitempty"`
 
+	// +kubebuilder:validation:Optional
+	// +operator-sdk:csv:customresourcedefinitions:type=spec
+	// NotificationsBusSection - Parameters related to the Notifications Bus services
+	NotificationsBus NotificationsBusSection `json:"notificationsBus,omitempty"`
+
 	// +kubebuilder:validation:Optional
 	// +operator-sdk:csv:customresourcedefinitions:type=spec
 	// Memcached - Parameters related to the Memcached service
@@ -484,10 +489,26 @@ type RabbitmqSection struct {
 
 	// +kubebuilder:validation:Optional
 	// +operator-sdk:csv:customresourcedefinitions:type=spec
-	// Templates - Overrides to use when creating the Rabbitmq clusters
+	// Templates - Overrides to use when creating the Rabbitmq clusters for RPC and (optionally) Notifications.
 	Templates *map[string]rabbitmqv1.RabbitMqSpecCore `json:"templates"`
 }
 
+// TODO(bogdando): keep this updated as the list of services that support this interface extends.
+
+// NotificationsBusSection defines the desired state of AMQP messaging Bus Services for producers and consumers of notifications
+type NotificationsBusSection struct {
+	// +kubebuilder:validation:Optional
+	// The name of RabbitMQ Cluster CR to select a Messaging
+	// Bus Service instance used by all services that produce or consume notifications.
+	// Avoid colocating it with RabbitMQ services used for PRC.
+	// That instance will be pushed down for services, unless overriden in templates.
+	// An empty value disables notifications drivers, and makes the services emitting no notifications at all.
+	// When undefined, no configuration will be pushed down for services, which provides backward compatibility during upgrades,
+	// and leaves a possibility for services to override the configuration, stick with its default behavior, or disable notifications only for itself.
+        // Services that support this global configuration interface include: Nova
+	RabbitMqClusterName *string `json:"rabbitMqClusterName,omitempty"`
+}
+
 // MemcachedSection defines the desired state of Memcached services
 type MemcachedSection struct {
 	// +kubebuilder:validation:Optional

apis/core/v1beta1/zz_generated.deepcopy.go

@@ -9662,6 +9662,11 @@ spec:
                 additionalProperties:
                   type: string
                 type: object
+              notificationsBus:
+                properties:
+                  rabbitMqClusterName:
+                    type: string
+                type: object
               nova:
                 properties:
                   apiOverride:

bindata/crds/crds.yaml

@@ -9498,6 +9498,11 @@ spec:
                 additionalProperties:
                   type: string
                 type: object
+              notificationsBus:
+                properties:
+                  rabbitMqClusterName:
+                    type: string
+                type: object
               nova:
                 properties:
                   apiOverride: