ROX-15587: Add basic Prometheus metrics (#1220)

Co-authored-by: Tom Martensen <tmartens@redhat.com>

service/cluster/cluster.go

@@ -12,6 +12,8 @@ import (
 	"sync"
 	"time"
 
+	"github.com/stackrox/infra/service/metrics"
+
 	argov3client "github.com/argoproj/argo-workflows/v3/cmd/argo/commands/client"
 	"github.com/argoproj/argo-workflows/v3/pkg/apiclient"
 	workflowpkg "github.com/argoproj/argo-workflows/v3/pkg/apiclient/workflow"
@@ -416,6 +418,8 @@ func (s *clusterImpl) create(req *v1.CreateClusterRequest, owner, eventID string
 		"cluster-id", clusterID,
 	)
 
+	metrics.FlavorsUsedCounter.WithLabelValues(flav.ID).Inc()
+
 	err = s.bqClient.InsertClusterCreationRecord(context.Background(), clusterID, created.GetName(), flav.GetID(), owner)
 	if err != nil {
 		log.Log(logging.WARN, "failed to record cluster creation", "cluster-id", clusterID, "error", err)

service/metrics/metrics.go

@@ -0,0 +1,20 @@
+package metrics
+
+import "github.com/prometheus/client_golang/prometheus"
+
+var (
+	// FlavorsUsedCounter is a Prometheus metric, counting the number of clusters created per flavor
+	FlavorsUsedCounter = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Namespace: "infra",
+			Name:      "flavors_used",
+			Help:      "Number of clusters created by flavor",
+		},
+		[]string{"flavor"},
+	)
+)
+
+func init() {
+	// Metrics have to be registered to be exposed:
+	prometheus.MustRegister(FlavorsUsedCounter)
+}