*: support discovery fallback

discovery/discovery.go

@@ -56,6 +56,10 @@ type Discoverer interface {
 	Discover() (string, error)
 }
 
+type ProxyDiscovery interface {
+	ProxyDiscover() (string, error)
+}
+
 type discovery struct {
 	cluster string
 	id      types.ID
@@ -97,6 +101,14 @@ func proxyFuncFromEnv() (func(*http.Request) (*url.URL, error), error) {
 }
 
 func New(durl string, id types.ID, config string) (Discoverer, error) {
+	return new(durl, id, config)
+}
+
+func ProxyNew(durl string) (ProxyDiscovery, error) {
+	return new(durl, 0, "")
+}
+
+func new(durl string, id types.ID, config string) (*discovery, error) {
 	u, err := url.Parse(durl)
 	if err != nil {
 		return nil, err
@@ -150,6 +162,22 @@ func (d *discovery) Discover() (string, error) {
 	return nodesToCluster(all), nil
 }
 
+func (d *discovery) ProxyDiscover() (string, error) {
+	nodes, size, err := d.checkCluster()
+	if err != nil {
+		if err == ErrFullCluster {
+			return nodesToCluster(nodes), nil
+		}
+		return "", err
+	}
+
+	all, err := d.waitNodes(nodes, size)
+	if err != nil {
+		return "", err
+	}
+	return nodesToCluster(all), nil
+}
+
 func (d *discovery) createSelf() error {
 	ctx, cancel := context.WithTimeout(context.Background(), client.DefaultRequestTimeout)
 	resp, err := d.c.Create(ctx, d.selfKey(), d.config, -1)
@@ -210,7 +238,7 @@ func (d *discovery) checkCluster() (client.Nodes, int, error) {
 			break
 		}
 		if i >= size-1 {
-			return nil, size, ErrFullCluster
+			return nodes[:size], size, ErrFullCluster
 		}
 	}
 	return nodes, size, nil

etcdmain/etcd.go

@@ -25,6 +25,7 @@ import (
 	"os"
 	"strings"
 
+	"github.com/coreos/etcd/discovery"
 	"github.com/coreos/etcd/etcdserver"
 	"github.com/coreos/etcd/etcdserver/etcdhttp"
 	"github.com/coreos/etcd/pkg/cors"
@@ -46,6 +47,7 @@ var (
 	name         = fs.String("name", "default", "Unique human-readable name for this node")
 	dir          = fs.String("data-dir", "", "Path to the data directory")
 	durl         = fs.String("discovery", "", "Discovery service used to bootstrap the cluster")
+	dfallback    = new(flags.Fallback)
 	snapCount    = fs.Uint64("snapshot-count", etcdserver.DefaultSnapCount, "Number of committed transactions to trigger a snapshot")
 	printVersion = fs.Bool("version", false, "Print the version and exit")
 
@@ -95,6 +97,11 @@ func init() {
 		// Should never happen.
 		log.Panicf("unexpected error setting up proxyFlag: %v", err)
 	}
+	fs.Var(dfallback, "discovery-fallback", fmt.Sprintf("Valid values include %s", strings.Join(flags.FallbackValues, ", ")))
+	if err := dfallback.Set(flags.FallbackProxy); err != nil {
+		// Should never happen.
+		log.Panicf("unexpected error setting up discovery-fallback flag: %v", err)
+	}
 
 	fs.StringVar(&clientTLSInfo.CAFile, "ca-file", "", "Path to the client server TLS CA file.")
 	fs.StringVar(&clientTLSInfo.CertFile, "cert-file", "", "Path to the client server TLS cert file.")
@@ -137,74 +144,97 @@ func Main() {
 	flags.SetFlagsFromEnv(fs)
 
 	if string(*proxyFlag) == flags.ProxyValueOff {
-		startEtcd()
-	} else {
-		startProxy()
+		if err := startEtcd(); err == nil {
+			// Block indefinitely
+			<-make(chan struct{})
+		} else {
+			if err == discovery.ErrFullCluster && *dfallback == flags.FallbackProxy {
+				fmt.Printf("etcd: dicovery cluster is full, falls back to %s", flags.FallbackProxy)
+			} else {
+				log.Fatalf("etcd: %v", err)
+			}
+		}
+	}
+	if err = startProxy(); err != nil {
+		log.Fatalf("proxy: %v", err)
 	}
-
 	// Block indefinitely
 	<-make(chan struct{})
 }
 
 // startEtcd launches the etcd server and HTTP handlers for client/server communication.
-func startEtcd() {
+func startEtcd() error {
 	cls, err := setupCluster()
 	if err != nil {
-		log.Fatalf("etcd: error setting up initial cluster: %v", err)
+		fmt.Errorf("error setting up initial cluster: %v", err)
 	}
 
 	if *dir == "" {
 		*dir = fmt.Sprintf("%v.etcd", *name)
-		log.Printf("etcd: no data-dir provided, using default data-dir ./%s", *dir)
+		fmt.Errorf("no data-dir provided, using default data-dir ./%s", *dir)
 	}
 	if err := os.MkdirAll(*dir, privateDirMode); err != nil {
-		log.Fatalf("etcd: cannot create data directory: %v", err)
+		fmt.Errorf("cannot create data directory: %v", err)
 	}
 	if err := fileutil.IsDirWriteable(*dir); err != nil {
-		log.Fatalf("etcd: cannot write to data directory: %v", err)
+		fmt.Errorf("cannot write to data directory: %v", err)
 	}
 
 	pt, err := transport.NewTransport(peerTLSInfo)
 	if err != nil {
-		log.Fatal(err)
+		return err
 	}
 
 	acurls, err := flags.URLsFromFlags(fs, "advertise-client-urls", "addr", clientTLSInfo)
 	if err != nil {
-		log.Fatal(err.Error())
+		return err
 	}
 
 	lpurls, err := flags.URLsFromFlags(fs, "listen-peer-urls", "peer-bind-addr", peerTLSInfo)
 	if err != nil {
-		log.Fatal(err.Error())
+		return err
 	}
 
 	plns := make([]net.Listener, 0)
 	for _, u := range lpurls {
-		l, err := transport.NewListener(u.Host, peerTLSInfo)
+		var l net.Listener
+		l, err = transport.NewListener(u.Host, peerTLSInfo)
 		if err != nil {
-			log.Fatal(err)
+			return err
 		}
 
 		urlStr := u.String()
 		log.Print("etcd: listening for peers on ", urlStr)
+		defer func() {
+			if err != nil {
+				l.Close()
+				log.Print("etcd: stopping listening for peers on ", urlStr)
+			}
+		}()
 		plns = append(plns, l)
 	}
 
 	lcurls, err := flags.URLsFromFlags(fs, "listen-client-urls", "bind-addr", clientTLSInfo)
 	if err != nil {
-		log.Fatal(err.Error())
+		return err
 	}
 
 	clns := make([]net.Listener, 0)
 	for _, u := range lcurls {
-		l, err := transport.NewListener(u.Host, clientTLSInfo)
+		var l net.Listener
+		l, err = transport.NewListener(u.Host, clientTLSInfo)
 		if err != nil {
-			log.Fatal(err)
+			return err
 		}
 
 		urlStr := u.String()
 		log.Print("etcd: listening for client requests on ", urlStr)
+		defer func() {
+			if err != nil {
+				l.Close()
+				log.Print("etcd: stopping listening for client requests on ", urlStr)
+			}
+		}()
 		clns = append(clns, l)
 	}
 
@@ -218,7 +248,11 @@ func startEtcd() {
 		ClusterState: *clusterState,
 		Transport:    pt,
 	}
-	s := etcdserver.NewServer(cfg)
+	var s *etcdserver.EtcdServer
+	s, err = etcdserver.NewServer(cfg)
+	if err != nil {
+		return err
+	}
 	s.Start()
 
 	ch := &cors.CORSHandler{
@@ -238,18 +272,33 @@ func startEtcd() {
 			log.Fatal(http.Serve(l, ch))
 		}(l)
 	}
+	return nil
 }
 
 // startProxy launches an HTTP proxy for client communication which proxies to other etcd nodes.
-func startProxy() {
+func startProxy() error {
 	cls, err := setupCluster()
 	if err != nil {
-		log.Fatalf("etcd: error setting up initial cluster: %v", err)
+		return fmt.Errorf("error setting up initial cluster: %v", err)
+	}
+
+	if *durl != "" {
+		d, err := discovery.ProxyNew(*durl)
+		if err != nil {
+			return fmt.Errorf("cannot init discovery %v", err)
+		}
+		s, err := d.ProxyDiscover()
+		if err != nil {
+			return err
+		}
+		if cls, err = etcdserver.NewClusterFromString(*durl, s); err != nil {
+			return err
+		}
 	}
 
 	pt, err := transport.NewTransport(clientTLSInfo)
 	if err != nil {
-		log.Fatal(err)
+		return err
 	}
 
 	// TODO(jonboulle): update peerURLs dynamically (i.e. when updating
@@ -258,7 +307,7 @@ func startProxy() {
 	uf := func() []string {
 		cls, err := etcdserver.GetClusterFromPeers(peerURLs)
 		if err != nil {
-			log.Printf("etcd: %v", err)
+			log.Printf("proxy: %v", err)
 			return []string{}
 		}
 		return cls.ClientURLs()
@@ -272,24 +321,24 @@ func startProxy() {
 	if string(*proxyFlag) == flags.ProxyValueReadonly {
 		ph = proxy.NewReadonlyHandler(ph)
 	}
-
 	lcurls, err := flags.URLsFromFlags(fs, "listen-client-urls", "bind-addr", clientTLSInfo)
 	if err != nil {
-		log.Fatal(err.Error())
+		return err
 	}
 	// Start a proxy server goroutine for each listen address
 	for _, u := range lcurls {
 		l, err := transport.NewListener(u.Host, clientTLSInfo)
 		if err != nil {
-			log.Fatal(err)
+			return err
 		}
 
 		host := u.Host
 		go func() {
-			log.Print("etcd: proxy listening for client requests on ", host)
+			log.Print("proxy: listening for client requests on ", host)
 			log.Fatal(http.Serve(l, ph))
 		}()
 	}
+	return nil
 }
 
 // setupCluster sets up the cluster definition for bootstrap or discovery.

etcdserver/server.go

@@ -175,9 +175,9 @@ type EtcdServer struct {
 
 // NewServer creates a new EtcdServer from the supplied configuration. The
 // configuration is considered static for the lifetime of the EtcdServer.
-func NewServer(cfg *ServerConfig) *EtcdServer {
+func NewServer(cfg *ServerConfig) (*EtcdServer, error) {
 	if err := os.MkdirAll(cfg.SnapDir(), privateDirMode); err != nil {
-		log.Fatalf("etcdserver: cannot create snapshot directory: %v", err)
+		return nil, fmt.Errorf("cannot create snapshot directory: %v", err)
 	}
 	ss := snap.New(cfg.SnapDir())
 	st := store.New()
@@ -192,27 +192,27 @@ func NewServer(cfg *ServerConfig) *EtcdServer {
 			log.Fatal(err)
 		}
 		if err := cfg.Cluster.ValidateAndAssignIDs(cl.Members()); err != nil {
-			log.Fatalf("etcdserver: error validating IDs from cluster %s: %v", cl, err)
+			return nil, fmt.Errorf("error validating IDs from cluster %s: %v", cl, err)
 		}
 		cfg.Cluster.SetID(cl.id)
 		cfg.Cluster.SetStore(st)
 		id, n, w = startNode(cfg, nil)
 	case !haveWAL && cfg.ClusterState == ClusterStateValueNew:
 		if err := cfg.VerifyBootstrapConfig(); err != nil {
-			log.Fatalf("etcdserver: %v", err)
+			return nil, err
 		}
 		m := cfg.Cluster.MemberByName(cfg.Name)
 		if cfg.ShouldDiscover() {
 			d, err := discovery.New(cfg.DiscoveryURL, m.ID, cfg.Cluster.String())
 			if err != nil {
-				log.Fatalf("etcdserver: cannot init discovery %v", err)
+				return nil, fmt.Errorf("cannot init discovery %v", err)
 			}
 			s, err := d.Discover()
 			if err != nil {
-				log.Fatalf("etcdserver: %v", err)
+				return nil, err
 			}
 			if cfg.Cluster, err = NewClusterFromString(cfg.Cluster.token, s); err != nil {
-				log.Fatalf("etcdserver: %v", err)
+				return nil, err
 			}
 		}
 		cfg.Cluster.SetStore(st)
@@ -225,7 +225,7 @@ func NewServer(cfg *ServerConfig) *EtcdServer {
 		var index uint64
 		snapshot, err := ss.Load()
 		if err != nil && err != snap.ErrNoSnapshot {
-			log.Fatal(err)
+			return nil, err
 		}
 		if snapshot != nil {
 			log.Printf("etcdserver: recovering from snapshot at index %d", snapshot.Index)
@@ -235,7 +235,7 @@ func NewServer(cfg *ServerConfig) *EtcdServer {
 		cfg.Cluster = NewClusterFromStore(cfg.Cluster.token, st)
 		id, n, w = restartNode(cfg, index, snapshot)
 	default:
-		log.Fatalf("etcdserver: unsupported bootstrap config")
+		return nil, fmt.Errorf("unsupported bootstrap config")
 	}
 
 	sstats := &stats.ServerStats{
@@ -261,7 +261,7 @@ func NewServer(cfg *ServerConfig) *EtcdServer {
 		SyncTicker: time.Tick(500 * time.Millisecond),
 		snapCount:  cfg.SnapCount,
 	}
-	return s
+	return s, nil
 }
 
 // Start prepares and starts server in a new goroutine. It is no longer safe to

hack/insta-discovery/Procfile

@@ -1,4 +1,6 @@
 # Use goreman to run `go get github.com/mattn/goreman`
+# One of the four etcd members falls back to a proxy
 etcd1: ../../bin/etcd -name infra1 -listen-client-urls http://127.0.0.1:4001 -advertise-client-urls http://127.0.0.1:4001 -listen-peer-urls http://127.0.0.1:7001 -initial-advertise-peer-urls http://127.0.0.1:7001
 etcd2: ../../bin/etcd -name infra2 -listen-client-urls http://127.0.0.1:4002 -advertise-client-urls http://127.0.0.1:4002 -listen-peer-urls http://127.0.0.1:7002 -initial-advertise-peer-urls http://127.0.0.1:7002
 etcd3: ../../bin/etcd -name infra3 -listen-client-urls http://127.0.0.1:4003 -advertise-client-urls http://127.0.0.1:4003 -listen-peer-urls http://127.0.0.1:7003 -initial-advertise-peer-urls http://127.0.0.1:7003
+etcd4: ../../bin/etcd -name infra4 -listen-client-urls http://127.0.0.1:4004 -advertise-client-urls http://127.0.0.1:4004 -listen-peer-urls http://127.0.0.1:7004 -initial-advertise-peer-urls http://127.0.0.1:7004

integration/cluster_test.go

@@ -176,7 +176,10 @@ type member struct {
 // Launch starts a member based on ServerConfig, PeerListeners
 // and ClientListeners.
 func (m *member) Launch(t *testing.T) {
-	m.s = etcdserver.NewServer(&m.ServerConfig)
+	var err error
+	if m.s, err = etcdserver.NewServer(&m.ServerConfig); err != nil {
+		t.Fatalf("failed to initialize the etcd server: %v", err)
+	}
 	m.s.Ticker = time.Tick(tickDuration)
 	m.s.SyncTicker = time.Tick(tickDuration)
 	m.s.Start()

pkg/flags/fallback.go

@@ -0,0 +1,53 @@
+/*
+   Copyright 2014 CoreOS, Inc.
+
+   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 flags
+
+import (
+	"errors"
+)
+
+const (
+	FallbackExit  = "exit"
+	FallbackProxy = "proxy"
+)
+
+var (
+	FallbackValues = []string{
+		FallbackExit,
+		FallbackProxy,
+	}
+)
+
+// FallbackFlag implements the flag.Value interface.
+type Fallback string
+
+// Set verifies the argument to be a valid member of FallbackFlagValues
+// before setting the underlying flag value.
+func (fb *Fallback) Set(s string) error {
+	for _, v := range FallbackValues {
+		if s == v {
+			*fb = Fallback(s)
+			return nil
+		}
+	}
+
+	return errors.New("invalid value")
+}
+
+func (fb *Fallback) String() string {
+	return string(*fb)
+}