Add health checker to leader election library

Author: verult

leaderelection/leader_election.go

@@ -20,6 +20,7 @@ import (
 	"context"
 	"fmt"
 	"io/ioutil"
+	"net/http"
 	"os"
 	"regexp"
 	"strings"
@@ -39,6 +40,14 @@ const (
 	defaultLeaseDuration = 15 * time.Second
 	defaultRenewDeadline = 10 * time.Second
 	defaultRetryPeriod   = 5 * time.Second
+
+	DefaultHealthCheckTimeout = 20 * time.Second
+
+	// HealthCheckerAddress is the address at which the leader election health
+	// checker reports status.
+	// The caller sidecar should document this address in appropriate flag
+	// descriptions.
+	HealthCheckerAddress = "/healthz/leader-election"
 )
 
 // leaderElection is a convenience wrapper around client-go's leader election library.
@@ -55,6 +64,9 @@ type leaderElection struct {
 	// valid options are resourcelock.LeasesResourceLock, resourcelock.EndpointsResourceLock,
 	// and resourcelock.ConfigMapsResourceLock
 	resourceLock string
+	// healthCheck reports unhealthy if leader election fails to renew leadership
+	// within a timeout period.
+	healthCheck *leaderelection.HealthzAdaptor
 
 	leaseDuration time.Duration
 	renewDeadline time.Duration
@@ -134,6 +146,27 @@ func (l *leaderElection) WithContext(ctx context.Context) {
 	l.ctx = ctx
 }
 
+// Server represents any type that could serve HTTP requests for the leader
+// election health check endpoint.
+type Server interface {
+	Handle(pattern string, handler http.Handler)
+}
+
+// PrepareHealthCheck creates a health check for this leader election object
+// with the given healthCheckTimeout and registers its HTTP handler to the given
+// server at the path specified by the constant "healthCheckerAddress".
+// healthCheckTimeout determines the max duration beyond lease expiration
+// allowed before reporting unhealthy.
+// The caller sidecar should document the handler address in appropriate flag
+// descriptions.
+func (l *leaderElection) PrepareHealthCheck(
+	s Server,
+	healthCheckTimeout time.Duration) {
+
+	l.healthCheck = leaderelection.NewLeaderHealthzAdaptor(healthCheckTimeout)
+	s.Handle(HealthCheckerAddress, adaptCheckToHandler(l.healthCheck.Check))
+}
+
 func (l *leaderElection) Run() error {
 	if l.identity == "" {
 		id, err := defaultLeaderElectionIdentity()
@@ -179,6 +212,7 @@ func (l *leaderElection) Run() error {
 				klog.V(3).Infof("new leader detected, current leader: %s", identity)
 			},
 		},
+		WatchDog: l.healthCheck,
 	}
 
 	ctx := l.ctx
@@ -220,3 +254,15 @@ func inClusterNamespace() string {
 
 	return "default"
 }
+
+// adaptCheckToHandler returns an http.HandlerFunc that serves the provided checks.
+func adaptCheckToHandler(c func(r *http.Request) error) http.HandlerFunc {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		err := c(r)
+		if err != nil {
+			http.Error(w, fmt.Sprintf("internal server error: %v", err), http.StatusInternalServerError)
+		} else {
+			fmt.Fprint(w, "ok")
+		}
+	})
+}

metrics/metrics.go

@@ -27,7 +27,6 @@ import (
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/status"
 	"k8s.io/component-base/metrics"
-	"k8s.io/klog/v2"
 )
 
 const (
@@ -90,10 +89,15 @@ type CSIMetricsManager interface {
 	// driverName - Name of the CSI driver against which this operation was executed.
 	SetDriverName(driverName string)
 
-	// StartMetricsEndpoint starts the metrics endpoint at the specified address/path
-	// for this metrics manager.
-	// If the metricsAddress is an empty string, this will be a no op.
-	StartMetricsEndpoint(metricsAddress, metricsPath string)
+	// RegisterToServer registers an HTTP handler for this metrics manager to the
+	// given server at the specified address/path.
+	RegisterToServer(s Server, metricsPath string)
+}
+
+// Server represents any type that could serve HTTP requests for the metrics
+// endpoint.
+type Server interface {
+	Handle(pattern string, handler http.Handler)
 }
 
 // MetricsManagerOption is used to pass optional configuration to a
@@ -325,27 +329,13 @@ func (cmm *csiMetricsManager) SetDriverName(driverName string) {
 	}
 }
 
-// StartMetricsEndpoint starts the metrics endpoint at the specified address/path
-// for this metrics manager  on a new go routine.
-// If the metricsAddress is an empty string, this will be a no op.
-func (cmm *csiMetricsManager) StartMetricsEndpoint(metricsAddress, metricsPath string) {
-	if metricsAddress == "" {
-		klog.Warningf("metrics endpoint will not be started because `metrics-address` was not specified.")
-		return
-	}
-
-	http.Handle(metricsPath, metrics.HandlerFor(
+// RegisterToServer registers an HTTP handler for this metrics manager to the
+// given server at the specified address/path.
+func (cmm *csiMetricsManager) RegisterToServer(s Server, metricsPath string) {
+	s.Handle(metricsPath, metrics.HandlerFor(
 		cmm.GetRegistry(),
 		metrics.HandlerOpts{
 			ErrorHandling: metrics.ContinueOnError}))
-
-	// Spawn a new go routine to listen on specified endpoint
-	go func() {
-		err := http.ListenAndServe(metricsAddress, nil)
-		if err != nil {
-			klog.Fatalf("Failed to start prometheus metrics endpoint on specified address (%q) and path (%q): %s", metricsAddress, metricsPath, err)
-		}
-	}()
 }
 
 // VerifyMetricsMatch is a helper function that verifies that the expected and

metrics/metrics_test.go

@@ -19,6 +19,7 @@ package metrics
 import (
 	"io/ioutil"
 	"net/http"
+	"net/http/httptest"
 	"strings"
 	"testing"
 	"time"
@@ -481,29 +482,26 @@ func TestRecordMetrics_Negative(t *testing.T) {
 	}
 }
 
-func TestStartMetricsEndPoint_Noop(t *testing.T) {
+func TestRegisterToServer_Noop(t *testing.T) {
 	// Arrange
 	cmm := NewCSIMetricsManagerForSidecar(
 		"fake.csi.driver.io" /* driverName */)
 	operationDuration, _ := time.ParseDuration("20s")
+	mux := http.NewServeMux()
 
 	// Act
-	cmm.StartMetricsEndpoint(":8080", "/metrics")
+	cmm.RegisterToServer(mux, "/metrics")
 	cmm.RecordMetrics(
 		"/csi.v1.Controller/ControllerGetCapabilities", /* operationName */
 		nil, /* operationErr */
 		operationDuration /* operationDuration */)
 
 	// Assert
-	request, err := http.NewRequest("GET", "http://localhost:8080/metrics", strings.NewReader(""))
-	if err != nil {
-		t.Fatalf("Creating request for metrics endpoint failed: %v", err)
-	}
-	client := &http.Client{}
-	resp, err := client.Do(request)
-	if err != nil {
-		t.Fatalf("Failed to GET metrics. Error: %v", err)
-	}
+	request := httptest.NewRequest("GET", "/metrics", strings.NewReader(""))
+	rec := httptest.NewRecorder()
+	mux.ServeHTTP(rec, request)
+	resp := rec.Result()
+
 	if resp.StatusCode != 200 {
 		t.Fatalf("/metrics response status not 200. Response was: %+v", resp)
 	}