Introduce a StatefulSet type elector builder (#1438)

* do not record for empty metric config

* Revert "do not record for empty metric config"

This reverts commit 539a5e4dbb.

* introduce statefulset builder

* change comment

* address victors comment and capsulation

* make exported func

* Update leaderelection/ordinal_test.go

Co-authored-by: Victor Agababov <vagababov@gmail.com>

* Update leaderelection/ordinal_test.go

Co-authored-by: Victor Agababov <vagababov@gmail.com>

* address comment

* format

* address comment from matt

Co-authored-by: Victor Agababov <vagababov@gmail.com>

leaderelection/config.go

@@ -126,6 +126,14 @@ type ComponentConfig struct {
 	RetryPeriod   time.Duration
 }
 
+// StatefulSetConfig represents the required information for a StatefulSet service.
+type StatefulSetConfig struct {
+	StatefulSetName string
+	ServiceName     string
+	Port            string
+	Protocol        string
+}
+
 func defaultComponentConfig(name string) ComponentConfig {
 	return ComponentConfig{
 		Component:   name,

leaderelection/context.go

@@ -28,6 +28,7 @@ import (
 	"k8s.io/client-go/tools/leaderelection"
 	"k8s.io/client-go/tools/leaderelection/resourcelock"
 	"knative.dev/pkg/logging"
+	"knative.dev/pkg/network"
 	"knative.dev/pkg/reconciler"
 	"knative.dev/pkg/system"
 )
@@ -42,6 +43,16 @@ func WithStandardLeaderElectorBuilder(ctx context.Context, kc kubernetes.Interfa
 	})
 }
 
+// WithStatefulSetLeaderElectorBuilder infuses a context with the ability to build
+// Electors which are assigned leadership based on the StatefulSet ordinal from
+// the provided component configuration.
+func WithStatefulSetLeaderElectorBuilder(ctx context.Context, cc ComponentConfig, ssc StatefulSetConfig) context.Context {
+	return context.WithValue(ctx, builderKey{}, &statefulSetBuilder{
+		lec: cc,
+		ssc: ssc,
+	})
+}
+
 // HasLeaderElection returns whether there is leader election configuration
 // associated with the context
 func HasLeaderElection(ctx context.Context) bool {
@@ -61,8 +72,9 @@ func BuildElector(ctx context.Context, la reconciler.LeaderAware, name string, e
 		switch builder := val.(type) {
 		case *standardBuilder:
 			return builder.BuildElector(ctx, la, name, enq)
+		case *statefulSetBuilder:
+			return builder.BuildElector(ctx, la, enq)
 		}
-		// TODO(mattmoor): Add a flavor of builder that relies on StatefulSet to partition the key space.
 	}
 
 	return &unopposedElector{
@@ -90,8 +102,9 @@ func (b *standardBuilder) BuildElector(ctx context.Context, la reconciler.Leader
 	buckets := make([]Elector, 0, b.lec.Buckets)
 	for i := uint32(0); i < b.lec.Buckets; i++ {
 		bkt := &bucket{
-			component: b.lec.Component,
-			name:      name,
+			// The resource name is the lowercase:
+			//   {component}.{workqueue}.{index}-of-{total}
+			name:  strings.ToLower(fmt.Sprintf("%s.%s.%02d-of-%02d", b.lec.Component, name, i, b.lec.Buckets)),
 			index: i,
 			total: b.lec.Buckets,
 		}
@@ -145,6 +158,35 @@ func (b *standardBuilder) BuildElector(ctx context.Context, la reconciler.Leader
 	return &runAll{les: buckets}, nil
 }
 
+type statefulSetBuilder struct {
+	lec ComponentConfig
+	ssc StatefulSetConfig
+}
+
+func (b *statefulSetBuilder) BuildElector(ctx context.Context, la reconciler.LeaderAware, enq func(reconciler.Bucket, types.NamespacedName)) (Elector, error) {
+	logger := logging.FromContext(ctx)
+
+	ordinal, err := ControllerOrdinal()
+	if err != nil {
+		return nil, err
+	}
+
+	logger.Infof("%s will run in StatefulSet ordinal assignement mode with ordinal %d", b.lec.Component, ordinal)
+
+	return &unopposedElector{
+		bkt: &bucket{
+			// The name is the full pod DNS of the owner pod of this bucket.
+			name: fmt.Sprintf("%s://%s-%d.%s.%s.svc.%s:%s", b.ssc.Protocol,
+				b.ssc.StatefulSetName, ordinal, b.ssc.ServiceName,
+				system.Namespace(), network.GetClusterDomainName(), b.ssc.Port),
+			index: uint32(ordinal),
+			total: b.lec.Buckets,
+		},
+		la:  la,
+		enq: enq,
+	}, nil
+}
+
 // unopposedElector promotes when run without needing to be elected.
 type unopposedElector struct {
 	bkt reconciler.Bucket
@@ -197,7 +239,6 @@ func (ruc *runUntilCancelled) Run(ctx context.Context) {
 }
 
 type bucket struct {
-	component string
 	name string
 
 	// We are bucket {index} of {total}
@@ -209,9 +250,7 @@ var _ reconciler.Bucket = (*bucket)(nil)
 
 // Name implements reconciler.Bucket
 func (b *bucket) Name() string {
-	// The resource name is the lowercase:
-	//   {component}.{workqueue}.{index}-of-{total}
-	return strings.ToLower(fmt.Sprintf("%s.%s.%02d-of-%02d", b.component, b.name, b.index, b.total))
+	return b.name
 }
 
 // Has implements reconciler.Bucket

leaderelection/context_test.go

@@ -21,6 +21,7 @@ package leaderelection
 
 import (
 	"context"
+	"os"
 	"testing"
 	"time"
 
@@ -95,7 +96,7 @@ func TestWithBuilder(t *testing.T) {
 
 	le, err := BuildElector(ctx, laf, "name", enq)
 	if err != nil {
-		t.Errorf("BuildElector() = %v", err)
+		t.Fatalf("BuildElector() = %v", err)
 	}
 
 	// We shouldn't see leases until we Run the elector.
@@ -144,3 +145,71 @@ func TestWithBuilder(t *testing.T) {
 		t.Fatal("Timed out waiting for demotion.")
 	}
 }
+
+func TestWithStatefulSetBuilder(t *testing.T) {
+	cc := ComponentConfig{
+		Component:   "component",
+		LeaderElect: true,
+		Buckets:     1,
+	}
+	podDNS := "ws://as-0.autoscaler.knative-testing.svc.cluster.local:8080"
+	ctx := context.Background()
+
+	promoted := make(chan struct{})
+	laf := &reconciler.LeaderAwareFuncs{
+		PromoteFunc: func(bkt reconciler.Bucket, enq func(reconciler.Bucket, types.NamespacedName)) error {
+			close(promoted)
+			return nil
+		},
+	}
+	enq := func(reconciler.Bucket, types.NamespacedName) {}
+
+	ctx = WithStatefulSetLeaderElectorBuilder(ctx, cc, StatefulSetConfig{
+		ServiceName:     "autoscaler",
+		StatefulSetName: "as",
+		Protocol:        "ws",
+		Port:            "8080",
+	})
+	if !HasLeaderElection(ctx) {
+		t.Error("HasLeaderElection() = false, wanted true")
+	}
+
+	le, err := BuildElector(ctx, laf, "name", enq)
+	if err == nil {
+		// controller ordinal env not set
+		t.Error("expected BuildElector() returns error but got none")
+	}
+
+	os.Setenv(controllerOrdinalEnv, "as-0")
+	defer os.Unsetenv(controllerOrdinalEnv)
+	le, err = BuildElector(ctx, laf, "name", enq)
+	if err != nil {
+		t.Fatalf("BuildElector() = %v", err)
+	}
+
+	ule, ok := le.(*unopposedElector)
+	if !ok {
+		t.Fatalf("BuildElector() = %T, wanted an unopposedElector", le)
+	}
+	if got, want := ule.bkt.Name(), podDNS; got != want {
+		t.Errorf("bkt.Name() = %s, wanted %s", got, want)
+	}
+
+	// Shouldn't be promoted until we Run the elector.
+	select {
+	case <-promoted:
+		t.Error("Got promoted, want no actions.")
+	default:
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	t.Cleanup(cancel)
+	go le.Run(ctx)
+
+	select {
+	case <-promoted:
+		// We expect to have been promoted.
+	case <-time.After(1 * time.Second):
+		t.Fatal("Timed out waiting for promotion.")
+	}
+}

leaderelection/ordinal.go

@@ -0,0 +1,39 @@
+/*
+Copyright 2020 The Knative Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package leaderelection
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+// If run a process on Kubernetes, the value of this environment variable
+// should be set to the pod name via the downward API.
+const controllerOrdinalEnv = "CONTROLLER_ORDINAL"
+
+// ControllerOrdinal tries to get ordinal from the pod name of a StatefulSet,
+// which is provided from the environment variable CONTROLLER_ORDINAL.
+func ControllerOrdinal() (uint64, error) {
+	v := os.Getenv(controllerOrdinalEnv)
+	if i := strings.LastIndex(v, "-"); i != -1 {
+		return strconv.ParseUint(v[i+1:], 10, 64)
+	}
+
+	return 0, fmt.Errorf("ordinal not found in %s=%s", controllerOrdinalEnv, v)
+}

leaderelection/ordinal_test.go

@@ -0,0 +1,72 @@
+/*
+Copyright 2020 The Knative Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package leaderelection
+
+import (
+	"fmt"
+	"os"
+	"testing"
+)
+
+func TestControllerOrdinal(t *testing.T) {
+	testCases := []struct {
+		testname string
+		podName  string
+		want     uint64
+		err      error
+	}{{
+		testname: "NotSet",
+		err:      fmt.Errorf("ordinal not found in %s=", controllerOrdinalEnv),
+	}, {
+		testname: "NoHyphen",
+		podName:  "as",
+		err:      fmt.Errorf("ordinal not found in %s=as", controllerOrdinalEnv),
+	}, {
+		testname: "InvalidOrdinal",
+		podName:  "as-invalid",
+		err:      fmt.Errorf(`strconv.ParseUint: parsing "invalid": invalid syntax`),
+	}, {
+		testname: "ValidName",
+		podName:  "as-0",
+	}, {
+		testname: "ValidName",
+		podName:  "as-1",
+		want:     1,
+	}}
+
+	defer os.Unsetenv(controllerOrdinalEnv)
+	for _, tt := range testCases {
+		t.Run(tt.testname, func(t *testing.T) {
+			if tt.podName != "" {
+				if os.Setenv(controllerOrdinalEnv, tt.podName) != nil {
+					t.Fatalf("fail to set env var %s=%s", controllerOrdinalEnv, tt.podName)
+				}
+			}
+
+			got, gotErr := ControllerOrdinal()
+			if tt.err != nil {
+				if gotErr == nil || gotErr.Error() != tt.err.Error() {
+					t.Errorf("got %v, want = %v, ", gotErr, tt.err)
+				}
+			} else if gotErr != nil {
+				t.Error("ControllerOrdinal() =", gotErr)
+			} else if got != tt.want {
+				t.Errorf("ControllerOrdinal() = %d, want = %d", got, tt.want)
+			}
+		})
+	}
+}