add refresher metric

cmd/aro/gateway.go

@@ -66,7 +66,7 @@ func gateway(ctx context.Context, log *logrus.Entry) error {
 		}
 	}
 
-	dbRefresher, err := pkgdbtoken.NewRefresher(log, _env, msiRefresherAuthorizer, insecureSkipVerify, dbc, "gateway")
+	dbRefresher, err := pkgdbtoken.NewRefresher(log, _env, msiRefresherAuthorizer, insecureSkipVerify, dbc, "gateway", m, "gateway")
 	if err != nil {
 		return err
 	}

pkg/dbtoken/refresher.go

@@ -15,6 +15,7 @@ import (
 
 	"github.com/Azure/ARO-RP/pkg/database/cosmosdb"
 	"github.com/Azure/ARO-RP/pkg/env"
+	"github.com/Azure/ARO-RP/pkg/metrics"
 	utilrecover "github.com/Azure/ARO-RP/pkg/util/recover"
 )
 
@@ -31,9 +32,12 @@ type refresher struct {
 	permission string
 
 	lastRefresh atomic.Value //time.Time
+
+	m            metrics.Interface
+	metricPrefix string
 }
 
-func NewRefresher(log *logrus.Entry, env env.Core, authorizer autorest.Authorizer, insecureSkipVerify bool, dbc cosmosdb.DatabaseClient, permission string) (Refresher, error) {
+func NewRefresher(log *logrus.Entry, env env.Core, authorizer autorest.Authorizer, insecureSkipVerify bool, dbc cosmosdb.DatabaseClient, permission string, m metrics.Interface, metricPrefix string) (Refresher, error) {
 	c, err := NewClient(env, authorizer, insecureSkipVerify)
 	if err != nil {
 		return nil, err
@@ -45,12 +49,17 @@ func NewRefresher(log *logrus.Entry, env env.Core, authorizer autorest.Authorize
 
 		dbc:        dbc,
 		permission: permission,
+
+		m:            m,
+		metricPrefix: metricPrefix,
 	}, nil
 }
 
 func (r *refresher) Run(ctx context.Context) error {
 	defer utilrecover.Panic(r.log)
 
+	go r.metrics()
+
 	t := time.NewTicker(10 * time.Second)
 	defer t.Stop()
 
@@ -66,6 +75,21 @@ func (r *refresher) Run(ctx context.Context) error {
 	}
 }
 
+func (r *refresher) metrics() {
+	defer utilrecover.Panic(r.log)
+
+	t := time.NewTicker(time.Minute)
+	defer t.Stop()
+
+	for {
+		if lastRefresh, ok := r.lastRefresh.Load().(time.Time); ok {
+			r.m.EmitGauge(r.metricPrefix+".lastrefresh", lastRefresh.Unix(), nil)
+		}
+
+		<-t.C
+	}
+}
+
 func (r *refresher) runOnce(ctx context.Context) (err error) {
 	// extra hardening to prevent a panic under runOnce taking out the refresher
 	// goroutine