Merge pull request #2539 from helinwang/master_etcd_1

Master save and load state from etcd, and register on etcd.

go/cmd/master/master.go

 package main
 
 import (
+	"fmt"
 	"net"
 	"net/http"
 	"net/rpc"
 	"strconv"
+	"strings"
 	"time"
 
 	"github.com/namsral/flag"
+	log "github.com/sirupsen/logrus"
 
 	"github.com/PaddlePaddle/Paddle/go/master"
+	"github.com/PaddlePaddle/Paddle/go/utils/networkhelper"
 )
 
 func main() {
 	port := flag.Int("port", 8080, "port of the master server.")
-
-	faultTolerance := flag.Bool("fault_tolerance", false, "enable fault tolerance (requires etcd).")
+	ttlSec := flag.Int("ttl", 60, "etcd lease TTL in seconds.")
+	endpoints := flag.String("endpoints", "http://127.0.0.1:2379", "comma separated etcd endpoints. If empty, fault tolerance will not be enabled.")
 	taskTimeoutDur := flag.Duration("task_timout_dur", 20*time.Minute, "task timout duration.")
 	taskTimeoutMax := flag.Int("task_timeout_max", 3, "max timtout count for each task before it being declared failed task.")
 	chunkPerTask := flag.Int("chunk_per_task", 10, "chunk per task.")
 	flag.Parse()
 
-	if *faultTolerance {
-		panic("fault tolernance not implemented.")
+	if *endpoints == "" {
+		log.Warningln("-endpoints not set, fault tolerance not be enabled.")
+	}
+
+	var store master.Store
+	if *endpoints != "" {
+		eps := strings.Split(*endpoints, ",")
+		ip, err := networkhelper.GetExternalIP()
+		if err != nil {
+			log.Fatal(err)
+		}
 
+		addr := fmt.Sprintf("%s:%d", ip, *port)
+		store, err = master.NewEtcdClient(eps, addr, master.DefaultLockPath, master.DefaultAddrPath, master.DefaultStatePath, *ttlSec)
+		if err != nil {
+			log.Fatal(err)
+		}
+	} else {
+		store = &master.InMemStore{}
+	}
+
+	s, err := master.NewService(store, *chunkPerTask, *taskTimeoutDur, *taskTimeoutMax)
+	if err != nil {
+		log.Fatal(err)
 	}
 
-	s := master.NewService(*chunkPerTask, *taskTimeoutDur, *taskTimeoutMax)
-	err := rpc.Register(s)
+	err = rpc.Register(s)
 	if err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 
 	rpc.HandleHTTP()
 	l, err := net.Listen("tcp", ":"+strconv.Itoa(*port))
 	if err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 
 	err = http.Serve(l, nil)
 	if err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 }

go/master/client_internal_test.go

@@ -47,9 +47,13 @@ func TestGetFinishTask(t *testing.T) {
 	}
 
 	go func(l net.Listener) {
-		s := NewService(chunkPerTask, time.Second, 1)
+		s, err := NewService(&InMemStore{}, chunkPerTask, time.Second, 1)
+		if err != nil {
+			panic(err)
+		}
+
 		server := rpc.NewServer()
-		err := server.Register(s)
+		err = server.Register(s)
 		if err != nil {
 			panic(err)
 		}

go/master/client_test.go

@@ -33,9 +33,13 @@ func TestNextRecord(t *testing.T) {
 	}
 
 	go func(l net.Listener) {
-		s := master.NewService(10, time.Second, 1)
+		s, err := master.NewService(&master.InMemStore{}, 10, time.Second, 1)
+		if err != nil {
+			panic(err)
+		}
+
 		server := rpc.NewServer()
-		err := server.Register(s)
+		err = server.Register(s)
 		if err != nil {
 			panic(err)
 		}

go/master/etcd_client.go

+package master
+
+import (
+	"context"
+	"time"
+
+	"github.com/coreos/etcd/clientv3"
+	"github.com/coreos/etcd/clientv3/concurrency"
+	log "github.com/sirupsen/logrus"
+)
+
+const (
+	// DefaultLockPath is the default etcd master lock path.
+	DefaultLockPath = "/master/lock"
+	// DefaultStatePath is the default etcd key for master state.
+	DefaultStatePath = "/master/state"
+	// DefaultAddrPath is the default etcd key for master address.
+	DefaultAddrPath = "/master/addr"
+)
+
+// EtcdClient is the etcd client that master uses for fault tolerance
+// and service registry.
+type EtcdClient struct {
+	lockPath  string
+	statePath string
+	client    *clientv3.Client
+	lock      *concurrency.Mutex
+}
+
+// NewEtcdClient creates a new EtcdClient.
+func NewEtcdClient(endpoints []string, addr string, lockPath, addrPath, statePath string, ttlSec int) (*EtcdClient, error) {
+	log.Debugf("Connecting to etcd at %v", endpoints)
+	// TODO(helin): gracefully shutdown etcd store. Becuase etcd
+	// store holds a etcd lock, even though the lock will expire
+	// when the lease timeout, we need to implement graceful
+	// shutdown to release the lock.
+	cli, err := clientv3.New(clientv3.Config{
+		Endpoints:   endpoints,
+		DialTimeout: dialTimeout,
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	sess, err := concurrency.NewSession(cli, concurrency.WithTTL(ttlSec))
+	if err != nil {
+		return nil, err
+	}
+
+	lock := concurrency.NewMutex(sess, lockPath)
+	// It's fine for the lock to get stuck, in this case we have
+	// multiple master servers running (only configured to have
+	// one master running, but split-brain problem may cuase
+	// multiple master servers running), and the cluster management
+	// software will kill one of them.
+	log.Debugf("Trying to acquire lock at %s.", lockPath)
+	err = lock.Lock(context.TODO())
+	if err != nil {
+		return nil, err
+	}
+	log.Debugf("Successfully acquired lock at %s.", lockPath)
+
+	put := clientv3.OpPut(addrPath, string(addr))
+	resp, err := cli.Txn(context.Background()).If(lock.IsOwner()).Then(put).Commit()
+	if err != nil {
+		return nil, err
+	}
+
+	if !resp.Succeeded {
+		log.Fatal("No longer owns the master lock. Exiting.")
+	}
+
+	e := &EtcdClient{
+		lockPath:  lockPath,
+		statePath: statePath,
+		client:    cli,
+		lock:      lock,
+	}
+
+	return e, nil
+}
+
+// Save saves the state into the etcd.
+func (e *EtcdClient) Save(state []byte) error {
+	ctx := context.TODO()
+	put := clientv3.OpPut(e.statePath, string(state))
+	resp, err := e.client.Txn(ctx).If(e.lock.IsOwner()).Then(put).Commit()
+	if err != nil {
+		return err
+	}
+
+	if !resp.Succeeded {
+		log.Errorln("No longer owns the lock, trying to lock again")
+		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+		err := e.lock.Lock(ctx)
+		cancel()
+		if err != nil {
+			// We lost the master lock and can not acquire
+			// it back, it means some other master is
+			// already started. We don't want cluster
+			// managment system to kill the master server
+			// who is holding the lock and running
+			// correctly. So the most feasible solution is
+			// to kill current master server. The current
+			// state is not saved, but the trainer's RPC
+			// call will fail, so the trainer will retry.
+			log.Fatalf("Could not acquire the lock at %s: %v. Exiting.", e.lockPath, err)
+		}
+		log.Infof("Successfully acquired lock at %s.", e.lockPath)
+		return e.Save(state)
+	}
+
+	return nil
+}
+
+// Load loads the state from etcd.
+func (e *EtcdClient) Load() ([]byte, error) {
+	ctx := context.TODO()
+	get := clientv3.OpGet(e.statePath)
+
+	resp, err := e.client.Txn(ctx).If(e.lock.IsOwner()).Then(get).Commit()
+	if err != nil {
+		return nil, err
+	}
+
+	if !resp.Succeeded {
+		log.Errorln("No longer owns the lock, trying to lock and load again.")
+		err = e.lock.Lock(context.Background())
+		if err != nil {
+			return nil, err
+		}
+
+		return e.Load()
+	}
+
+	kvs := resp.Responses[0].GetResponseRange().Kvs
+	if len(kvs) == 0 {
+		// No state exists
+		return nil, nil
+	}
+
+	state := kvs[0].Value
+	return state, nil
+}

go/master/inmem_store.go

+package master
+
+import "sync"
+
+// InMemStore is an in memory implementation of Store interface.
+//
+// It does not tolerate the fault that casues the program to crash.
+type InMemStore struct {
+	mu  sync.Mutex
+	buf []byte
+}
+
+// Save saves the state into the in-memory store.
+func (m *InMemStore) Save(state []byte) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	m.buf = state
+	return nil
+}
+
+// Load loads the state from the in-memory store.
+func (m *InMemStore) Load() ([]byte, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	return m.buf, nil
+}

go/master/service.go

 package master
 
 import (
+	"bytes"
+	"compress/gzip"
+	"encoding/gob"
 	"errors"
 	"os"
 	"path/filepath"
@@ -12,24 +15,54 @@ import (
 	"github.com/PaddlePaddle/recordio"
 )
 
+const (
+	dialTimeout = 5 * time.Second
+)
+
+// Store is the interface for save and load the master state.
+type Store interface {
+	Save([]byte) error
+	Load() ([]byte, error)
+}
+
+// Chunk is a chunk of data consisted of several data instances.
+type Chunk struct {
+	Path  string
+	Index recordio.Index // chunk index
+}
+
+// Task is the basic unit of data instances assigned to trainers.
+type Task struct {
+	ID     int
+	Chunks []Chunk
+}
+
+type taskEntry struct {
+	Epoch      int
+	NumTimeout int
+	Task       Task
+}
+
+type taskQueues struct {
+	Todo    []taskEntry
+	Pending map[int]taskEntry // map from task ID to task entry
+	Done    []taskEntry
+	Failed  []Task
+}
+
 // Service is the master server service.
 type Service struct {
 	chunksPerTask int
 	timeoutDur    time.Duration
 	timeoutMax    int
 	ready         chan struct{}
+	store         Store
 
 	mu         sync.Mutex
 	initDone   bool
 	taskQueues taskQueues
 }
 
-// Recover recovers service state from etcd.
-func Recover() (*Service, error) {
-	// TODO(helin): recover from snapshot state from etcd.
-	return nil, nil
-}
-
 func partition(chunks []Chunk, chunksPerTask int) []taskEntry {
 	id := 0
 	if chunksPerTask <= 0 {
@@ -58,7 +91,7 @@ func partition(chunks []Chunk, chunksPerTask int) []taskEntry {
 }
 
 // NewService creates a new service.
-func NewService(chunksPerTask int, timeoutDur time.Duration, timeoutMax int) *Service {
+func NewService(store Store, chunksPerTask int, timeoutDur time.Duration, timeoutMax int) (*Service, error) {
 	s := &Service{}
 	s.chunksPerTask = chunksPerTask
 	s.timeoutDur = timeoutDur
@@ -66,38 +99,82 @@ func NewService(chunksPerTask int, timeoutDur time.Duration, timeoutMax int) *Se
 	s.taskQueues = taskQueues{}
 	s.taskQueues.Pending = make(map[int]taskEntry)
 	s.ready = make(chan struct{})
-	return s
-}
+	s.store = store
+	recovered, err := s.recover()
+	if err != nil {
+		return nil, err
+	}
 
-// Chunk is a chunk of data consisted of several data instances.
-type Chunk struct {
-	Path  string
-	Index recordio.Index // chunk index
-}
+	if recovered {
+		// Recovered. Now the state is already initialized,
+		// and the master is ready.
+		s.initDone = true
+		close(s.ready)
+		log.Info("Master recovered from saved state.")
+	}
 
-// Task is the basic unit of data instances assigned to trainers.
-type Task struct {
-	ID     int
-	Chunks []Chunk
+	return s, nil
 }
 
-type taskEntry struct {
-	Epoch      int
-	NumTimeout int
-	Task       Task
-}
+// recover recovers service state from etcd.
+func (s *Service) recover() (bool, error) {
+	state, err := s.store.Load()
+	if err != nil {
+		return false, err
+	}
 
-type taskQueues struct {
-	Todo    []taskEntry
-	Pending map[int]taskEntry // map from task ID to task entry
-	Done    []taskEntry
-	Failed  []Task
+	if state == nil {
+		log.Infoln("No state exists, not recovered.")
+		return false, nil
+	}
+
+	log.Infof("Loaded snapshot of size: %d bytes.", len(state))
+	gr, err := gzip.NewReader(bytes.NewReader(state))
+	if err != nil {
+		return false, err
+	}
+
+	dec := gob.NewDecoder(gr)
+	var tqs taskQueues
+	err = dec.Decode(&tqs)
+	if err != nil {
+		return false, err
+	}
+
+	err = gr.Close()
+	if err != nil {
+		// Only close failed, recover actually succeed, so
+		// just log error.
+		log.Errorln(err)
+	}
+
+	s.taskQueues = tqs
+	return true, nil
 }
 
-// *must* be called with s.mu being held.
+// snapshot *must* be called with s.mu being held.
 func (s *Service) snapshot() error {
-	// TODO(helin): snapshot state on etcd.
-	return nil
+	// TOOD(helin): etcd request has a size limit, so the snapshot
+	// size is limited by the max request size. We should either
+	// divide the snapshot into smaller chunks and save under
+	// different keys, or configure the request size to be big
+	// enough:
+	// https://github.com/coreos/etcd/blob/2f84f3d8d8ed8f9537ab6ffa44a3a1c7eddfa9b1/embed/config.go#L44
+	var buf bytes.Buffer
+	gw := gzip.NewWriter(&buf)
+	enc := gob.NewEncoder(gw)
+	err := enc.Encode(s.taskQueues)
+	if err != nil {
+		return err
+	}
+	err = gw.Close()
+	if err != nil {
+		return err
+	}
+
+	state := buf.Bytes()
+	log.Infof("Saving snapshot of size: %d bytes.", len(state))
+	return s.store.Save(state)
 }
 
 func readChunks(globPaths []string) ([]Chunk, error) {
@@ -207,12 +284,12 @@ func (s *Service) checkTimeoutFunc(taskID int, epoch int) func() {
 
 		t.NumTimeout++
 		if t.NumTimeout > s.timeoutMax {
-			log.Warningf("Task %v timed out %d times, discard.\n", t.Task, t.NumTimeout)
+			log.Warningf("Task %v timed out %d times, discard.", t.Task, t.NumTimeout)
 			s.taskQueues.Failed = append(s.taskQueues.Failed, t.Task)
 			return
 		}
 
-		log.Warningf("Task %v timed out %d times, retry.\n", t.Task, t.NumTimeout)
+		log.Warningf("Task %v timed out %d times, retry.", t.Task, t.NumTimeout)
 		s.taskQueues.Todo = append(s.taskQueues.Todo, t)
 	}
 }

go/pserver/cclient/cclient.go

@@ -133,7 +133,7 @@ func paddle_init_param(client C.paddle_pserver_client, param C.paddle_parameter,
 
 	if err != nil {
 		if err.Error() == pserver.AlreadyInitialized {
-			log.Warningf("parameter %s already initialized, treat paddle_init_param as sucessful.\n", name)
+			log.Warningf("parameter %s already initialized, treat paddle_init_param as sucessful.", name)
 			return C.PSERVER_OK
 		}
 		log.Errorln(err)
@@ -200,7 +200,7 @@ func paddle_get_params(client C.paddle_pserver_client, dst **C.paddle_parameter,
 		for i, p := range ps {
 			pn[i] = p.Name
 		}
-		log.Errorf("pserver returned wrong number of parameters. Requested: %s, returned: %s.\n", strings.Join(pn, ", "), strings.Join(ns, ", "))
+		log.Errorf("pserver returned wrong number of parameters. Requested: %s, returned: %s.", strings.Join(pn, ", "), strings.Join(ns, ", "))
 		return C.PSERVER_ERROR
 	}
 
@@ -210,7 +210,7 @@ func paddle_get_params(client C.paddle_pserver_client, dst **C.paddle_parameter,
 			for i, p := range ps {
 				pn[i] = p.Name
 			}
-			log.Errorf("pserver returned wrong parameters, or not in requested order. Requested: %s, returned: %s.\n", strings.Join(pn, ", "), strings.Join(ns, ", "))
+			log.Errorf("pserver returned wrong parameters, or not in requested order. Requested: %s, returned: %s.", strings.Join(pn, ", "), strings.Join(ns, ", "))
 			return C.PSERVER_ERROR
 		}
 	}