Add defaulting to leader election

Author: JoelSpeed

pkg/leaderelection/leader_election.go

@@ -18,6 +18,7 @@ package leaderelection
 
 import (
 	"fmt"
+	"io/ioutil"
 	"os"
 
 	"k8s.io/apimachinery/pkg/util/uuid"
@@ -27,6 +28,8 @@ import (
 	"sigs.k8s.io/controller-runtime/pkg/recorder"
 )
 
+const inClusterNamespacePath = "/var/run/secrets/kubernetes.io/serviceaccount/namespace"
+
 // Options provides the required configuration to create a new resource lock
 type Options struct {
 	// LeaderElection determines whether or not to use leader election when
@@ -49,8 +52,18 @@ func NewResourceLock(config *rest.Config, recorderProvider recorder.Provider, op
 		return nil, nil
 	}
 
-	if options.LeaderElectionID == "" || options.LeaderElectionNamespace == "" {
-		return nil, fmt.Errorf("if leader election is enabled, both LeaderElectionID and LeaderElectionNamespace must be set")
+	// Default the LeaderElectionID
+	if options.LeaderElectionID == "" {
+		options.LeaderElectionID = "controller-runtime"
+	}
+
+	// Default the namespace (if running in cluster)
+	if options.LeaderElectionNamespace == "" {
+		var err error
+		options.LeaderElectionNamespace, err = getInClusterNamespace()
+		if err != nil {
+			return nil, fmt.Errorf("unable to find leader election namespace: %v", err)
+		}
 	}
 
 	// Leader id, needs to be unique
@@ -76,3 +89,21 @@ func NewResourceLock(config *rest.Config, recorderProvider recorder.Provider, op
 			EventRecorder: recorderProvider.GetEventRecorderFor(id),
 		})
 }
+
+func getInClusterNamespace() (string, error) {
+	// Check whether the namespace file exists.
+	// If not, we are not running in cluster so can't guess the namespace.
+	_, err := os.Stat(inClusterNamespacePath)
+	if os.IsNotExist(err) {
+		return "", fmt.Errorf("not running in-cluster, please specify LeaderElectionNamespace")
+	} else if err != nil {
+		return "", fmt.Errorf("error checking namespace file: %v", err)
+	}
+
+	// Load the namespace file and return itss content
+	namespace, err := ioutil.ReadFile(inClusterNamespacePath)
+	if err != nil {
+		return "", fmt.Errorf("error reading namespace file: %v", err)
+	}
+	return string(namespace), nil
+}

pkg/manager/internal.go

@@ -139,6 +139,10 @@ func (cm *controllerManager) GetRecorder(name string) record.EventRecorder {
 	return cm.recorderProvider.GetEventRecorderFor(name)
 }
 
+func (cm *controllerManager) GetResourceLock() resourcelock.Interface {
+	return cm.resourceLock
+}
+
 func (cm *controllerManager) Start(stop <-chan struct{}) error {
 	if cm.resourceLock == nil {
 		go cm.start(stop)

pkg/manager/manager.go

@@ -67,6 +67,9 @@ type Manager interface {
 
 	// GetRecorder returns a new EventRecorder for the provided name
 	GetRecorder(name string) record.EventRecorder
+
+	// GetResourceLock returns an initialized ResourceLock
+	GetResourceLock() resourcelock.Interface
 }
 
 // Options are the arguments for creating a new Manager

pkg/manager/manager_test.go

@@ -97,18 +97,18 @@ var _ = Describe("manger.Manager", func() {
 			close(done)
 		})
 		Context("with leader election enabled", func() {
-			It("should return an error if ID not set", func() {
+			It("should default ID to controller-runtime if ID is not set", func() {
 				m, err := New(cfg, Options{LeaderElection: true, LeaderElectionNamespace: "default"})
-				Expect(m).To(BeNil())
-				Expect(err).To(HaveOccurred())
-				Expect(err.Error()).To(ContainSubstring("if leader election is enabled, both LeaderElectionID and LeaderElectionNamespace must be set"))
+				Expect(m).ToNot(BeNil())
+				Expect(err).ToNot(HaveOccurred())
+				Expect(m.GetResourceLock().Describe()).To(Equal("default/controller-runtime"))
 			})
 
-			It("should return an error if namespace not set", func() {
+			It("should return an error if namespace not set and not running in cluster", func() {
 				m, err := New(cfg, Options{LeaderElection: true, LeaderElectionID: "controller-runtime"})
 				Expect(m).To(BeNil())
 				Expect(err).To(HaveOccurred())
-				Expect(err.Error()).To(ContainSubstring("if leader election is enabled, both LeaderElectionID and LeaderElectionNamespace must be set"))
+				Expect(err.Error()).To(ContainSubstring("unable to find leader election namespace: not running in-cluster, please specify LeaderElectionNamespace"))
 			})
 		})
 	})