Add helpers to stop and start metrics/profile servers

These are used throughout the Submariner project.

Signed-off-by: Stephen Kitt <[email protected]>

pkg/util/helpers.go

@@ -19,11 +19,16 @@ limitations under the License.
 package util
 
 import (
+	"context"
 	"crypto/x509"
 	"fmt"
+	"net/http"
+	"net/http/pprof"
 	"sync/atomic"
+	"time"
 
 	"github.com/pkg/errors"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"github.com/submariner-io/admiral/pkg/resource"
 	"k8s.io/apimachinery/pkg/api/meta"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
@@ -171,3 +176,40 @@ func AddCertificateErrorHandler(fatal bool) {
 		// The generic handler has already logged the error, no need to repeat if we don't want extra detail
 	})
 }
+
+// StartMetricsAndProfileServer starts an HTTP server providing access to Prometheus metrics
+// and/or profiling information.
+// The returned server should be shut down on process exit, using StopMetricsAndProfileServer().
+func StartMetricsAndProfileServer(metrics, profile bool, port int) *http.Server {
+	if !metrics && !profile {
+		return nil
+	}
+
+	srv := &http.Server{Addr: fmt.Sprintf(":%d", port), ReadHeaderTimeout: 60 * time.Second}
+
+	if metrics {
+		http.Handle("/metrics", promhttp.Handler())
+	}
+	if profile {
+		http.HandleFunc("/debug", pprof.Profile)
+	}
+
+	go func() {
+		if err := srv.ListenAndServe(); !errors.Is(err, http.ErrServerClosed) {
+			logger.Errorf(err, "Error starting metrics/profile HTTP server")
+		}
+	}()
+
+	return srv
+}
+
+// StopMetricsAndProfileServer stops the given HTTP server, if any.
+func StopMetricsAndProfileServer(srv *http.Server) {
+	if srv == nil {
+		return
+	}
+
+	if err := srv.Shutdown(context.TODO()); err != nil {
+		logger.Errorf(err, "Error shutting down metrics/profile HTTP server")
+	}
+}