pkg/metrics: add an updater function to CreateServiceMonitors (#1991)

With this addition it would be possible to provide a list of updater
functions to modify the ServiceMonitor after they are created and
before they are added to k8. This can be used for scenarios like
updating the labels on the ServiceMonitor, changing metadata or updating
exposed endpoints (service port); or literally any other change that a
user might need.

Signed-off-by: Alex Lourie <[email protected]>

Author: alourie

hack/tests/sanity-check.sh

@@ -2,6 +2,7 @@
 set -ex
 
 go vet ./...
+go fmt ./...
 ./hack/check_license.sh
 ./hack/check_error_log_msg_format.sh
 

pkg/metrics/service-monitor.go

@@ -28,9 +28,11 @@ import (
 
 var ErrServiceMonitorNotPresent = fmt.Errorf("no ServiceMonitor registered with the API")
 
+type ServiceMonitorUpdater func(*monitoringv1.ServiceMonitor) error
+
 // CreateServiceMonitors creates ServiceMonitors objects based on an array of Service objects.
 // If CR ServiceMonitor is not registered in the Cluster it will not attempt at creating resources.
-func CreateServiceMonitors(config *rest.Config, ns string, services []*v1.Service) ([]*monitoringv1.ServiceMonitor, error) {
+func CreateServiceMonitors(config *rest.Config, ns string, services []*v1.Service, updaters ...ServiceMonitorUpdater) ([]*monitoringv1.ServiceMonitor, error) {
 	// check if we can even create ServiceMonitors
 	exists, err := hasServiceMonitor(config)
 	if err != nil {
@@ -48,6 +50,12 @@ func CreateServiceMonitors(config *rest.Config, ns string, services []*v1.Servic
 			continue
 		}
 		sm := GenerateServiceMonitor(s)
+		for _, update := range updaters {
+			if err := update(sm); err != nil {
+				return nil, err
+			}
+		}
+
 		smc, err := mclient.ServiceMonitors(ns).Create(sm)
 		if err != nil {
 			return serviceMonitors, err