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/manager_test.go

@@ -24,9 +24,11 @@ import (
 	"k8s.io/apimachinery/pkg/api/meta"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/client-go/rest"
+	"k8s.io/client-go/tools/leaderelection/resourcelock"
 	"sigs.k8s.io/controller-runtime/pkg/cache"
 	"sigs.k8s.io/controller-runtime/pkg/cache/informertest"
 	"sigs.k8s.io/controller-runtime/pkg/client"
+	"sigs.k8s.io/controller-runtime/pkg/leaderelection"
 	fakeleaderelection "sigs.k8s.io/controller-runtime/pkg/leaderelection/fake"
 	"sigs.k8s.io/controller-runtime/pkg/reconcile"
 	"sigs.k8s.io/controller-runtime/pkg/recorder"
@@ -97,18 +99,27 @@ var _ = Describe("manger.Manager", func() {
 			close(done)
 		})
 		Context("with leader election enabled", func() {
-			It("should return an error if ID 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"))
+			It("should default ID to controller-runtime if ID is not set", func() {
+				var rl resourcelock.Interface
+				m, err := New(cfg, Options{
+					LeaderElection:          true,
+					LeaderElectionNamespace: "default",
+					newResourceLock: func(config *rest.Config, recorderProvider recorder.Provider, options leaderelection.Options) (resourcelock.Interface, error) {
+						var err error
+						rl, err = leaderelection.NewResourceLock(config, recorderProvider, options)
+						return rl, err
+					},
+				})
+				Expect(m).ToNot(BeNil())
+				Expect(err).ToNot(HaveOccurred())
+				Expect(rl.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"))
 			})
 		})
 	})