fix(agent): allow serial order for servers connection per instance (#…

…6020)


* enforce serial order on agent connections

* add serial order for dataflow engine

* move logging after acquiring lock

* lint fixes

* add tests for chainer subscribe

* increase sleep to fix flaky test

scheduler/pkg/agent/server.go

@@ -112,6 +112,7 @@ type Server struct {
 	certificateStore          *seldontls.CertificateStore
 	waiter                    *modelRelocatedWaiter // waiter for when we want to drain a particular server replica
 	autoscalingServiceEnabled bool
+	agentMutex                sync.Map // to force a serial order per agent (serverName, replicaIdx)
 }
 
 type SchedulerAgent interface {
@@ -138,6 +139,7 @@ func NewAgentServer(
 		scheduler:                 scheduler,
 		waiter:                    newModelRelocatedWaiter(),
 		autoscalingServiceEnabled: autoscalingServiceEnabled,
+		agentMutex:                sync.Map{},
 	}
 
 	hub.RegisterModelEventHandler(
@@ -383,12 +385,20 @@ func (s *Server) ModelScalingTrigger(stream pb.AgentService_ModelScalingTriggerS
 
 func (s *Server) Subscribe(request *pb.AgentSubscribeRequest, stream pb.AgentService_SubscribeServer) error {
 	logger := s.logger.WithField("func", "Subscribe")
+	key := ServerKey{serverName: request.ServerName, replicaIdx: request.ReplicaIdx}
+
+	// this is forcing a serial order per agent (serverName, replicaIdx)
+	// in general this will make sure that a given agent disconnects fully before another agent is allowed to connect
+	mu, _ := s.agentMutex.LoadOrStore(key, &sync.Mutex{})
+	mu.(*sync.Mutex).Lock()
+	defer mu.(*sync.Mutex).Unlock()
+
 	logger.Infof("Received subscribe request from %s:%d", request.ServerName, request.ReplicaIdx)
 
 	fin := make(chan bool)
 
 	s.mutex.Lock()
-	s.agents[ServerKey{serverName: request.ServerName, replicaIdx: request.ReplicaIdx}] = &AgentSubscriber{
+	s.agents[key] = &AgentSubscriber{
 		finished: fin,
 		stream:   stream,
 	}
@@ -414,7 +424,7 @@ func (s *Server) Subscribe(request *pb.AgentSubscribeRequest, stream pb.AgentSer
 		case <-ctx.Done():
 			logger.Infof("Client replica %s:%d has disconnected", request.ServerName, request.ReplicaIdx)
 			s.mutex.Lock()
-			delete(s.agents, ServerKey{serverName: request.ServerName, replicaIdx: request.ReplicaIdx})
+			delete(s.agents, key)
 			s.mutex.Unlock()
 			s.removeServerReplicaImpl(request.GetServerName(), int(request.GetReplicaIdx())) // this is non-blocking beyond rescheduling models on removed server
 			return nil

scheduler/pkg/agent/server_test.go

@@ -10,21 +10,39 @@ the Change License after the Change Date as each is defined in accordance with t
 package agent
 
 import (
+	"context"
 	"fmt"
 	"testing"
 	"time"
 
 	. "github.com/onsi/gomega"
 	log "github.com/sirupsen/logrus"
 	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
 
+	"github.com/seldonio/seldon-core/apis/go/v2/mlops/agent"
 	pb "github.com/seldonio/seldon-core/apis/go/v2/mlops/agent"
 	pbs "github.com/seldonio/seldon-core/apis/go/v2/mlops/scheduler"
 
 	"github.com/seldonio/seldon-core/scheduler/v2/pkg/coordinator"
+	testing_utils "github.com/seldonio/seldon-core/scheduler/v2/pkg/internal/testing_utils"
+	"github.com/seldonio/seldon-core/scheduler/v2/pkg/scheduler"
 	"github.com/seldonio/seldon-core/scheduler/v2/pkg/store"
 )
 
+type mockScheduler struct {
+}
+
+var _ scheduler.Scheduler = (*mockScheduler)(nil)
+
+func (s mockScheduler) Schedule(_ string) error {
+	return nil
+}
+
+func (s mockScheduler) ScheduleFailedModels() ([]string, error) {
+	return nil, nil
+}
+
 type mockStore struct {
 	models map[string]*store.ModelSnapshot
 }
@@ -91,15 +109,15 @@ func (m *mockStore) UpdateModelState(modelKey string, version uint32, serverKey
 }
 
 func (m *mockStore) AddServerReplica(request *pb.AgentSubscribeRequest) error {
-	panic("implement me")
+	return nil
 }
 
 func (m *mockStore) ServerNotify(request *pbs.ServerNotify) error {
 	panic("implement me")
 }
 
 func (m *mockStore) RemoveServerReplica(serverName string, replicaIdx int) ([]string, error) {
-	panic("implement me")
+	return nil, nil
 }
 
 func (m *mockStore) DrainServerReplica(serverName string, replicaIdx int) ([]string, error) {
@@ -943,3 +961,112 @@ func TestAutoscalingEnabled(t *testing.T) {
 	}
 
 }
+
+func TestSubscribe(t *testing.T) {
+	log.SetLevel(log.DebugLevel)
+	g := NewGomegaWithT(t)
+
+	type ag struct {
+		id      uint32
+		doClose bool
+	}
+	type test struct {
+		name                          string
+		agents                        []ag
+		expectedAgentsCount           int
+		expectedAgentsCountAfterClose int
+	}
+	tests := []test{
+		{
+			name: "simple",
+			agents: []ag{
+				{1, true}, {2, true},
+			},
+			expectedAgentsCount:           2,
+			expectedAgentsCountAfterClose: 0,
+		},
+		{
+			name: "simple - no close",
+			agents: []ag{
+				{1, true}, {2, false},
+			},
+			expectedAgentsCount:           2,
+			expectedAgentsCountAfterClose: 1,
+		},
+		{
+			name: "duplicates",
+			agents: []ag{
+				{1, true}, {1, false},
+			},
+			expectedAgentsCount:           1,
+			expectedAgentsCountAfterClose: 1,
+		},
+		{
+			name: "duplicates with all close",
+			agents: []ag{
+				{1, true}, {1, true}, {1, true},
+			},
+			expectedAgentsCount:           1,
+			expectedAgentsCountAfterClose: 0,
+		},
+	}
+
+	getStream := func(id uint32, context context.Context, port int) *grpc.ClientConn {
+		conn, _ := grpc.NewClient(fmt.Sprintf(":%d", port), grpc.WithTransportCredentials(insecure.NewCredentials()))
+		grpcClient := agent.NewAgentServiceClient(conn)
+		_, _ = grpcClient.Subscribe(
+			context,
+			&agent.AgentSubscribeRequest{
+				ServerName:           "dummy",
+				ReplicaIdx:           id,
+				ReplicaConfig:        &agent.ReplicaConfig{},
+				Shared:               true,
+				AvailableMemoryBytes: 0,
+			},
+		)
+		return conn
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			logger := log.New()
+			eventHub, err := coordinator.NewEventHub(logger)
+			g.Expect(err).To(BeNil())
+			server := NewAgentServer(logger, &mockStore{}, mockScheduler{}, eventHub, false)
+			port, err := testing_utils.GetFreePortForTest()
+			if err != nil {
+				t.Fatal(err)
+			}
+			err = server.startServer(uint(port), false)
+			if err != nil {
+				t.Fatal(err)
+			}
+			time.Sleep(100 * time.Millisecond)
+
+			streams := make([]*grpc.ClientConn, 0)
+			for _, a := range test.agents {
+				go func(id uint32) {
+					conn := getStream(id, context.Background(), port)
+					streams = append(streams, conn)
+				}(a.id)
+			}
+
+			time.Sleep(500 * time.Millisecond)
+
+			g.Expect(len(server.agents)).To(Equal(test.expectedAgentsCount))
+
+			for idx, s := range streams {
+				go func(idx int, s *grpc.ClientConn) {
+					if test.agents[idx].doClose {
+						s.Close()
+					}
+				}(idx, s)
+			}
+
+			time.Sleep(10 * time.Second)
+
+			g.Expect(len(server.agents)).To(Equal(test.expectedAgentsCountAfterClose))
+
+			server.StopAgentStreams()
+		})
+	}
+}

scheduler/pkg/kafka/dataflow/server.go

@@ -44,6 +44,7 @@ type ChainerServer struct {
 	pipelineHandler pipeline.PipelineHandler
 	topicNamer      *kafka.TopicNamer
 	loadBalancer    util.LoadBalancer
+	chainerMutex    sync.Map
 	chainer.UnimplementedChainerServer
 }
 
@@ -66,6 +67,7 @@ func NewChainerServer(logger log.FieldLogger, eventHub *coordinator.EventHub, pi
 		pipelineHandler: pipelineHandler,
 		topicNamer:      topicNamer,
 		loadBalancer:    loadBalancer,
+		chainerMutex:    sync.Map{},
 	}
 
 	eventHub.RegisterPipelineEventHandler(
@@ -125,17 +127,25 @@ func (c *ChainerServer) PipelineUpdateEvent(ctx context.Context, message *chaine
 
 func (c *ChainerServer) SubscribePipelineUpdates(req *chainer.PipelineSubscriptionRequest, stream chainer.Chainer_SubscribePipelineUpdatesServer) error {
 	logger := c.logger.WithField("func", "SubscribePipelineStatus")
+
+	key := req.GetName()
+	// this is forcing a serial order per dataflow-engine
+	// in general this will make sure that a given dataflow-engine disconnects fully before another dataflow-engine is allowed to connect
+	mu, _ := c.chainerMutex.LoadOrStore(key, &sync.Mutex{})
+	mu.(*sync.Mutex).Lock()
+	defer mu.(*sync.Mutex).Unlock()
+
 	logger.Infof("Received subscribe request from %s", req.GetName())
 
 	fin := make(chan bool)
 
 	c.mu.Lock()
-	c.streams[req.Name] = &ChainerSubscription{
-		name:   req.Name,
+	c.streams[key] = &ChainerSubscription{
+		name:   key,
 		stream: stream,
 		fin:    fin,
 	}
-	c.loadBalancer.AddServer(req.Name)
+	c.loadBalancer.AddServer(key)
 	c.mu.Unlock()
 
 	// Handle addition of new server
@@ -148,13 +158,13 @@ func (c *ChainerServer) SubscribePipelineUpdates(req *chainer.PipelineSubscripti
 	for {
 		select {
 		case <-fin:
-			logger.Infof("Closing stream for %s", req.GetName())
+			logger.Infof("Closing stream for %s", key)
 			return nil
 		case <-ctx.Done():
-			logger.Infof("Stream disconnected %s", req.GetName())
+			logger.Infof("Stream disconnected %s", key)
 			c.mu.Lock()
-			c.loadBalancer.RemoveServer(req.Name)
-			delete(c.streams, req.Name)
+			c.loadBalancer.RemoveServer(key)
+			delete(c.streams, key)
 			c.mu.Unlock()
 			// Handle removal of server
 			c.rebalance()