fix: Add validation method for agent pre-requisite

Move prometheus-agent pre-requisites to validation
function `Runnable()` to avoid creating prometheusagentcontroller
incase of validation failure.

Signed-off-by: Jayapriya Pai <slashpai9@gmail.com>

cmd/operator/main.go

@@ -266,11 +266,20 @@ func Main() int {
 		return 1
 	}
 
-	pao, err := prometheusagentcontroller.New(ctx, cfg, log.With(logger, "component", "prometheusagentoperator"), r)
-	if err != nil {
-		fmt.Fprint(os.Stderr, "instantiating prometheus-agent controller failed: ", err)
-		cancel()
-		return 1
+	var pao *prometheusagentcontroller.Operator
+	ok, err := prometheusagentcontroller.Runnable(ctx, cfg, log.With(logger, "component", "prometheusagentoperator"))
+
+	if !ok && err != nil {
+		fmt.Fprint(os.Stderr, "pre-requistes for prometheus-agent controller failed: ", err)
+	}
+
+	if ok {
+		pao, err = prometheusagentcontroller.New(ctx, cfg, log.With(logger, "component", "prometheusagentoperator"), r)
+		if err != nil {
+			fmt.Fprint(os.Stderr, "instantiating prometheus-agent controller failed: ", err)
+			cancel()
+			return 1
+		}
 	}
 
 	ao, err := alertmanagercontroller.New(ctx, cfg, log.With(logger, "component", "alertmanageroperator"), r)
@@ -360,7 +369,9 @@ func Main() int {
 	}))
 
 	wg.Go(func() error { return po.Run(ctx) })
-	wg.Go(func() error { return pao.Run(ctx) })
+	if pao != nil {
+		wg.Go(func() error { return pao.Run(ctx) })
+	}
 	wg.Go(func() error { return ao.Run(ctx) })
 	wg.Go(func() error { return to.Run(ctx) })
 

pkg/k8sutil/k8sutil.go

@@ -25,6 +25,8 @@ import (
 	"strings"
 
 	"github.com/cespare/xxhash/v2"
+	"github.com/go-kit/log"
+	"github.com/go-kit/log/level"
 	monitoringv1 "github.com/prometheus-operator/prometheus-operator/pkg/apis/monitoring/v1"
 	monitoringv1alpha1 "github.com/prometheus-operator/prometheus-operator/pkg/apis/monitoring/v1alpha1"
 	monitoringv1beta1 "github.com/prometheus-operator/prometheus-operator/pkg/apis/monitoring/v1beta1"
@@ -37,6 +39,7 @@ import (
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/util/validation"
 	"k8s.io/client-go/discovery"
+	"k8s.io/client-go/kubernetes"
 	clientappsv1 "k8s.io/client-go/kubernetes/typed/apps/v1"
 	clientv1 "k8s.io/client-go/kubernetes/typed/core/v1"
 	"k8s.io/client-go/rest"
@@ -114,6 +117,27 @@ func NewClusterConfig(host string, tlsInsecure bool, tlsConfig *rest.TLSClientCo
 	return cfg, nil
 }
 
+func CreateK8sClient(cfg *rest.Config) (*kubernetes.Clientset, error) {
+	client, err := kubernetes.NewForConfig(cfg)
+	if err != nil {
+		return nil, err
+	}
+	return client, nil
+}
+
+func IsCRDInstalled(resource string, groupVersion string, kclient *kubernetes.Clientset, logger log.Logger) (bool, error) {
+	crdInstalled, err := IsAPIGroupVersionResourceSupported(kclient.Discovery(), groupVersion, resource)
+	if err != nil {
+		level.Warn(logger).Log("msg", "failed to check if the API supports the PrometheusAgent CRD", "err ", err)
+		return false, err
+	}
+	if !crdInstalled {
+		level.Info(logger).Log("msg", "Prometheus agent controller disabled because the PrometheusAgent CRD isn't installed")
+		return false, err
+	}
+	return true, nil
+}
+
 func IsResourceNotFoundError(err error) bool {
 	se, ok := err.(*apierrors.StatusError)
 	if !ok {

pkg/prometheus/agent/operator.go

@@ -46,6 +46,7 @@ import (
 	"k8s.io/apimachinery/pkg/fields"
 	"k8s.io/apimachinery/pkg/labels"
 	"k8s.io/client-go/kubernetes"
+	"k8s.io/client-go/rest"
 	"k8s.io/client-go/tools/cache"
 )
 
@@ -82,14 +83,55 @@ type Operator struct {
 	endpointSliceSupported bool
 }
 
+func createK8sClusterConfig(conf operator.Config) (*rest.Config, error) {
+	cfg, err := k8sutil.NewClusterConfig(conf.Host, conf.TLSInsecure, &conf.TLSConfig)
+	if err != nil {
+		return nil, err
+	}
+
+	return cfg, nil
+}
+
+func Runnable(ctx context.Context, conf operator.Config, logger log.Logger) (bool, error) {
+	cfg, err := createK8sClusterConfig(conf)
+	if err != nil {
+		return false, errors.Wrap(err, "instantiating cluster config failed")
+	}
+
+	kclient, err := k8sutil.CreateK8sClient(cfg)
+	if err != nil {
+		return false, errors.Wrap(err, "instantiating kubernetes client failed")
+	}
+
+	crdInstalled, err := k8sutil.IsCRDInstalled(monitoringv1alpha1.SchemeGroupVersion.String(), monitoringv1alpha1.PrometheusAgentName, kclient, logger)
+	if !crdInstalled {
+		return false, err
+	}
+
+	verbs := map[string][]string{
+		monitoringv1alpha1.PrometheusAgentName:                           {"get", "list", "watch"},
+		fmt.Sprintf("%s/status", monitoringv1alpha1.PrometheusAgentName): {"update"},
+	}
+	missingPermissions, err := getMissingPermissions(ctx, kclient, conf, verbs)
+	if err != nil {
+		return false, err
+	}
+	if len(missingPermissions) > 0 {
+		level.Warn(logger).Log("msg", "Prometheus agent controller disabled because it lacks the required permissions on PrometheusAgent objects", "missingpermissions", fmt.Sprintf("%v", missingPermissions))
+		return false, nil
+	}
+
+	return true, nil
+}
+
 // New creates a new controller.
 func New(ctx context.Context, conf operator.Config, logger log.Logger, r prometheus.Registerer) (*Operator, error) {
-	cfg, err := k8sutil.NewClusterConfig(conf.Host, conf.TLSInsecure, &conf.TLSConfig)
+	cfg, err := createK8sClusterConfig(conf)
 	if err != nil {
 		return nil, errors.Wrap(err, "instantiating cluster config failed")
 	}
 
-	client, err := kubernetes.NewForConfig(cfg)
+	client, err := k8sutil.CreateK8sClient(cfg)
 	if err != nil {
 		return nil, errors.Wrap(err, "instantiating kubernetes client failed")
 	}
@@ -282,25 +324,6 @@ func New(ctx context.Context, conf operator.Config, logger log.Logger, r prometh
 
 // Run the controller.
 func (c *Operator) Run(ctx context.Context) error {
-	crdInstalled, err := k8sutil.IsAPIGroupVersionResourceSupported(c.kclient.Discovery(), monitoringv1alpha1.SchemeGroupVersion.String(), monitoringv1alpha1.PrometheusAgentName)
-	if err != nil {
-		level.Warn(c.logger).Log("msg", "failed to check if the API supports the PrometheusAgent CRD", "err ", err)
-		return nil
-	}
-	if !crdInstalled {
-		level.Info(c.logger).Log("msg", "Prometheus agent controller disabled because the PrometheusAgent CRD isn't installed")
-		return nil
-	}
-
-	missingPermissions, err := c.getMissingPermissions(ctx)
-	if err != nil {
-		return err
-	}
-	if len(missingPermissions) > 0 {
-		level.Warn(c.logger).Log("msg", "Prometheus agent controller disabled because it lacks the required permissions on PrometheusAgent objects", "missingpermissions", fmt.Sprintf("%v", missingPermissions))
-		return nil
-	}
-
 	errChan := make(chan error)
 	go func() {
 		v, err := c.kclient.Discovery().ServerVersion()
@@ -1335,18 +1358,14 @@ func (c *Operator) handleMonitorNamespaceUpdate(oldo, curo interface{}) {
 
 // getMissingPermissions returns the RBAC permissions that the controller would need to be
 // granted to fulfill its mission. An empty map means that everything is ok.
-func (c *Operator) getMissingPermissions(ctx context.Context) (map[string][]string, error) {
-	verbs := map[string][]string{
-		monitoringv1alpha1.PrometheusAgentName:                           {"get", "list", "watch"},
-		fmt.Sprintf("%s/status", monitoringv1alpha1.PrometheusAgentName): {"update"},
-	}
+func getMissingPermissions(ctx context.Context, kclient *kubernetes.Clientset, conf operator.Config, verbs map[string][]string) (map[string][]string, error) {
 	var ssar *authv1.SelfSubjectAccessReview
 	var ssarResponse *authv1.SelfSubjectAccessReview
 	var err error
 
 	missingPermissions := map[string][]string{}
 
-	for ns := range c.config.Namespaces.PrometheusAllowList {
+	for ns := range conf.Namespaces.PrometheusAllowList {
 		for resource, verbs := range verbs {
 			for _, verb := range verbs {
 				ssar = &authv1.SelfSubjectAccessReview{
@@ -1360,7 +1379,7 @@ func (c *Operator) getMissingPermissions(ctx context.Context) (map[string][]stri
 						},
 					},
 				}
-				ssarResponse, err = c.kclient.AuthorizationV1().SelfSubjectAccessReviews().Create(ctx, ssar, metav1.CreateOptions{})
+				ssarResponse, err = kclient.AuthorizationV1().SelfSubjectAccessReviews().Create(ctx, ssar, metav1.CreateOptions{})
 				if err != nil {
 					return nil, err
 				}