Use etcd compare and swap to update the list of pods, to remove a race.

api/examples/controller.json

@@ -7,6 +7,7 @@
         "desiredState": {
            "manifest": {
              "containers": [{
+               "name": "nginx",
                "image": "dockerfile/nginx",
                "ports": [{"containerPort": 80, "hostPort": 8080}]
              }]

cmd/integration/integration.go

@@ -23,6 +23,7 @@ import (
 	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
+	"runtime"
 	"time"
 
 	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
@@ -36,6 +37,7 @@ import (
 )
 
 func main() {
+	runtime.GOMAXPROCS(4)
 	util.InitLogs()
 	defer util.FlushLogs()
 
@@ -51,7 +53,7 @@ func main() {
 
 	controllerManager := controller.MakeReplicationManager(etcd.NewClient(servers), client.New(apiserver.URL, nil))
 
-	controllerManager.Run(10 * time.Second)
+	controllerManager.Run(1 * time.Second)
 
 	// Kublet
 	fakeDocker1 := &kubelet.FakeDockerClient{}
@@ -102,7 +104,7 @@ func main() {
 	// Validate that they're truly up.
 	pods, err := kubeClient.ListPods(nil)
 	if err != nil || len(pods.Items) != 2 {
-		glog.Fatal("FAILED")
+		glog.Fatal("FAILED: %#v", pods.Items)
 	}
 
 	// Check that kubelet tried to make the pods.
@@ -124,7 +126,7 @@ func main() {
 	// We expect 5: 2 net containers + 2 pods from the replication controller +
 	//              1 net container + 2 pods from the URL.
 	if len(createdPods) != 7 {
-		glog.Fatalf("Unexpected list of created pods: %#v\n", createdPods)
+		glog.Fatalf("Unexpected list of created pods: %#v %#v %#v\n", createdPods, fakeDocker1.Created, fakeDocker2.Created)
 	}
 	glog.Infof("OK")
 }
@@ -146,6 +148,7 @@ const (
 	// This is copied from, and should be kept in sync with:
 	// https://raw.githubusercontent.com/GoogleCloudPlatform/container-vm-guestbook-redis-python/master/manifest.yaml
 	testManifestFile = `version: v1beta1
+id: web-test
 containers:
   - name: redis
     image: dockerfile/redis

pkg/registry/etcd_registry.go

@@ -90,13 +90,17 @@ func makeContainerKey(machine string) string {
 	return "/registry/hosts/" + machine + "/kubelet"
 }
 
-func (registry *EtcdRegistry) loadManifests(machine string) (manifests []api.ContainerManifest, err error) {
-	err = registry.helper().ExtractObj(makeContainerKey(machine), &manifests, true)
-	return
+func (registry *EtcdRegistry) loadManifests(machine string) (manifests []api.ContainerManifest, index uint64, err error) {
+	err, index = registry.helper().ExtractObj(makeContainerKey(machine), &manifests, true)
+	return manifests, index, err
 }
 
-func (registry *EtcdRegistry) updateManifests(machine string, manifests []api.ContainerManifest) error {
-	return registry.helper().SetObj(makeContainerKey(machine), manifests)
+func (registry *EtcdRegistry) updateManifests(machine string, manifests []api.ContainerManifest, index uint64) error {
+	if index != 0 {
+		return registry.helper().CompareAndSwapObj(makeContainerKey(machine), manifests, index)
+	} else {
+		return registry.helper().SetObj(makeContainerKey(machine), manifests)
+	}
 }
 
 func (registry *EtcdRegistry) CreatePod(machineIn string, pod api.Pod) error {
@@ -108,7 +112,7 @@ func (registry *EtcdRegistry) CreatePod(machineIn string, pod api.Pod) error {
 }
 
 func (registry *EtcdRegistry) runPod(pod api.Pod, machine string) error {
-	manifests, err := registry.loadManifests(machine)
+	manifests, index, err := registry.loadManifests(machine)
 	if err != nil {
 		return err
 	}
@@ -124,8 +128,18 @@ func (registry *EtcdRegistry) runPod(pod api.Pod, machine string) error {
 	if err != nil {
 		return err
 	}
-	manifests = append(manifests, manifest)
-	return registry.updateManifests(machine, manifests)
+	for {
+		manifests = append(manifests, manifest)
+		err = registry.updateManifests(machine, manifests, index)
+		if util.IsEtcdConflict(err) {
+			manifests, index, err = registry.loadManifests(machine)
+			if err != nil {
+				return err
+			}
+			continue
+		}
+		return err
+	}
 }
 
 func (registry *EtcdRegistry) UpdatePod(pod api.Pod) error {
@@ -141,36 +155,42 @@ func (registry *EtcdRegistry) DeletePod(podID string) error {
 }
 
 func (registry *EtcdRegistry) deletePodFromMachine(machine, podID string) error {
-	manifests, err := registry.loadManifests(machine)
-	if err != nil {
-		return err
-	}
-	newManifests := make([]api.ContainerManifest, 0)
-	found := false
-	for _, manifest := range manifests {
-		if manifest.Id != podID {
-			newManifests = append(newManifests, manifest)
-		} else {
-			found = true
+	for {
+		manifests, index, err := registry.loadManifests(machine)
+		if err != nil {
+			return err
 		}
-	}
-	if !found {
-		// This really shouldn't happen, it indicates something is broken, and likely
-		// there is a lost pod somewhere.
-		// However it is "deleted" so log it and move on
-		glog.Infof("Couldn't find: %s in %#v", podID, manifests)
-	}
-	if err = registry.updateManifests(machine, newManifests); err != nil {
-		return err
+		newManifests := make([]api.ContainerManifest, 0)
+		found := false
+		for _, manifest := range manifests {
+			if manifest.Id != podID {
+				newManifests = append(newManifests, manifest)
+			} else {
+				found = true
+			}
+		}
+		if !found {
+			// This really shouldn't happen, it indicates something is broken, and likely
+			// there is a lost pod somewhere.
+			// However it is "deleted" so log it and move on
+			glog.Infof("Couldn't find: %s in %#v", podID, manifests)
+		}
+		if err = registry.updateManifests(machine, newManifests, index); err != nil {
+			if util.IsEtcdConflict(err) {
+				continue
+			}
+			return err
+		}
+		break
 	}
 	key := makePodKey(machine, podID)
-	_, err = registry.etcdClient.Delete(key, true)
+	_, err := registry.etcdClient.Delete(key, true)
 	return err
 }
 
 func (registry *EtcdRegistry) getPodForMachine(machine, podID string) (pod api.Pod, err error) {
 	key := makePodKey(machine, podID)
-	err = registry.helper().ExtractObj(key, &pod, false)
+	err, _ = registry.helper().ExtractObj(key, &pod, false)
 	if err != nil {
 		return
 	}
@@ -205,7 +225,7 @@ func makeControllerKey(id string) string {
 func (registry *EtcdRegistry) GetController(controllerID string) (*api.ReplicationController, error) {
 	var controller api.ReplicationController
 	key := makeControllerKey(controllerID)
-	err := registry.helper().ExtractObj(key, &controller, false)
+	err, _ := registry.helper().ExtractObj(key, &controller, false)
 	if err != nil {
 		return nil, err
 	}
@@ -244,7 +264,7 @@ func (registry *EtcdRegistry) CreateService(svc api.Service) error {
 func (registry *EtcdRegistry) GetService(name string) (*api.Service, error) {
 	key := makeServiceKey(name)
 	var svc api.Service
-	err := registry.helper().ExtractObj(key, &svc, false)
+	err, _ := registry.helper().ExtractObj(key, &svc, false)
 	if err != nil {
 		return nil, err
 	}

pkg/registry/etcd_registry_test.go

@@ -640,3 +640,18 @@ func TestEtcdUpdateEndpoints(t *testing.T) {
 		t.Errorf("Unexpected endpoints: %#v, expected %#v", endpointsOut, endpoints)
 	}
 }
+
+// TODO We need a test for the compare and swap behavior.  This basically requires two things:
+//   1) Add a per-operation synchronization channel to the fake etcd client, such that any operation waits on that
+//      channel, this will enable us to orchestrate the flow of etcd requests in the test.
+//   2) We need to make the map from key to (response, error) actually be a [](response, error) and pop
+//      our way through the responses.  That will enable us to hand back multiple different responses for
+//      the same key.
+//   Once that infrastructure is in place, the test looks something like:
+//      Routine #1                               Routine #2
+//         Read
+//         Wait for sync on update               Read
+//                                               Update
+//         Update
+//   In the buggy case, this will result in lost data.  In the correct case, the second update should fail
+//   and be retried.

pkg/util/etcd_tools.go

@@ -24,10 +24,24 @@ import (
 	"github.com/coreos/go-etcd/etcd"
 )
 
+// EtcdClient is an injectable interface for testing.
+type EtcdClient interface {
+	AddChild(key, data string, ttl uint64) (*etcd.Response, error)
+	Get(key string, sort, recursive bool) (*etcd.Response, error)
+	Set(key, value string, ttl uint64) (*etcd.Response, error)
+	Create(key, value string, ttl uint64) (*etcd.Response, error)
+	CompareAndSwap(key, value string, ttl uint64, prevValue string, prevIndex uint64) (*etcd.Response, error)
+	Delete(key string, recursive bool) (*etcd.Response, error)
+	// I'd like to use directional channels here (e.g. <-chan) but this interface mimics
+	// the etcd client interface which doesn't, and it doesn't seem worth it to wrap the api.
+	Watch(prefix string, waitIndex uint64, recursive bool, receiver chan *etcd.Response, stop chan bool) (*etcd.Response, error)
+}
+
 // Interface exposing only the etcd operations needed by EtcdHelper.
 type EtcdGetSet interface {
 	Get(key string, sort, recursive bool) (*etcd.Response, error)
 	Set(key, value string, ttl uint64) (*etcd.Response, error)
+	CompareAndSwap(key, value string, ttl uint64, prevValue string, prevIndex uint64) (*etcd.Response, error)
 }
 
 // EtcdHelper offers common object marshalling/unmarshalling operations on an etcd client.
@@ -37,6 +51,16 @@ type EtcdHelper struct {
 
 // Returns true iff err is an etcd not found error.
 func IsEtcdNotFound(err error) bool {
+	return isEtcdErrorNum(err, 100)
+}
+
+// Returns true iff err is an etcd write conflict.
+func IsEtcdConflict(err error) bool {
+	return isEtcdErrorNum(err, 101)
+}
+
+// Returns true iff err is an etcd error, whose errorCode matches errorCode
+func isEtcdErrorNum(err error, errorCode int) bool {
 	if err == nil {
 		return false
 	}
@@ -46,7 +70,7 @@ func IsEtcdNotFound(err error) bool {
 		if etcdError == nil {
 			return false
 		}
-		if etcdError.ErrorCode == 100 {
+		if etcdError.ErrorCode == errorCode {
 			return true
 		}
 	}
@@ -92,23 +116,33 @@ func (h *EtcdHelper) ExtractList(key string, slicePtr interface{}) error {
 // Unmarshals json found at key into objPtr. On a not found error, will either return
 // a zero object of the requested type, or an error, depending on ignoreNotFound. Treats
 // empty responses and nil response nodes exactly like a not found error.
-func (h *EtcdHelper) ExtractObj(key string, objPtr interface{}, ignoreNotFound bool) error {
+func (h *EtcdHelper) ExtractObj(key string, objPtr interface{}, ignoreNotFound bool) (error, uint64) {
 	response, err := h.Client.Get(key, false, false)
 
 	if err != nil && !IsEtcdNotFound(err) {
-		return err
+		return err, 0
 	}
 	if err != nil || response.Node == nil || len(response.Node.Value) == 0 {
 		if ignoreNotFound {
 			pv := reflect.ValueOf(objPtr)
 			pv.Elem().Set(reflect.Zero(pv.Type().Elem()))
-			return nil
+			return nil, 0
 		} else if err != nil {
-			return err
+			return err, 0
 		}
-		return fmt.Errorf("key '%v' found no nodes field: %#v", key, response)
+		return fmt.Errorf("key '%v' found no nodes field: %#v", key, response), 0
 	}
-	return json.Unmarshal([]byte(response.Node.Value), objPtr)
+	return json.Unmarshal([]byte(response.Node.Value), objPtr), response.Node.ModifiedIndex
+}
+
+// CompareAndSwapObj marshals obj via json, and stores under key so long as index matches the previous modified index
+func (h *EtcdHelper) CompareAndSwapObj(key string, obj interface{}, index uint64) error {
+	data, err := json.Marshal(obj)
+	if err != nil {
+		return err
+	}
+	_, err = h.Client.CompareAndSwap(key, string(data), 0, "", index)
+	return err
 }
 
 // SetObj marshals obj via json, and stores under key.

pkg/util/etcd_tools_test.go

@@ -86,7 +86,7 @@ func TestExtractObj(t *testing.T) {
 	fakeClient.Set("/some/key", MakeJSONString(expect), 0)
 	helper := EtcdHelper{fakeClient}
 	var got testMarshalType
-	err := helper.ExtractObj("/some/key", &got, false)
+	err, _ := helper.ExtractObj("/some/key", &got, false)
 	if err != nil {
 		t.Errorf("Unexpected error %#v", err)
 	}
@@ -120,11 +120,11 @@ func TestExtractObjNotFoundErr(t *testing.T) {
 	helper := EtcdHelper{fakeClient}
 	try := func(key string) {
 		var got testMarshalType
-		err := helper.ExtractObj(key, &got, false)
+		err, _ := helper.ExtractObj(key, &got, false)
 		if err == nil {
 			t.Errorf("%s: wanted error but didn't get one", key)
 		}
-		err = helper.ExtractObj(key, &got, true)
+		err, _ = helper.ExtractObj(key, &got, true)
 		if err != nil {
 			t.Errorf("%s: didn't want error but got %#v", key, err)
 		}

pkg/util/fake_etcd_client.go

@@ -23,18 +23,6 @@ import (
 	"github.com/coreos/go-etcd/etcd"
 )
 
-// EtcdClient is an injectable interface for testing.
-type EtcdClient interface {
-	AddChild(key, data string, ttl uint64) (*etcd.Response, error)
-	Get(key string, sort, recursive bool) (*etcd.Response, error)
-	Set(key, value string, ttl uint64) (*etcd.Response, error)
-	Create(key, value string, ttl uint64) (*etcd.Response, error)
-	Delete(key string, recursive bool) (*etcd.Response, error)
-	// I'd like to use directional channels here (e.g. <-chan) but this interface mimics
-	// the etcd client interface which doesn't, and it doesn't seem worth it to wrap the api.
-	Watch(prefix string, waitIndex uint64, recursive bool, receiver chan *etcd.Response, stop chan bool) (*etcd.Response, error)
-}
-
 type EtcdResponseWithError struct {
 	R *etcd.Response
 	E error
@@ -87,6 +75,12 @@ func (f *FakeEtcdClient) Set(key, value string, ttl uint64) (*etcd.Response, err
 	f.Data[key] = result
 	return result.R, f.Err
 }
+
+func (f *FakeEtcdClient) CompareAndSwap(key, value string, ttl uint64, prevValue string, prevIndex uint64) (*etcd.Response, error) {
+	// TODO: Maybe actually implement compare and swap here?
+	return f.Set(key, value, ttl)
+}
+
 func (f *FakeEtcdClient) Create(key, value string, ttl uint64) (*etcd.Response, error) {
 	return f.Set(key, value, ttl)
 }