Add expect bootstrap '-expect=n' mode.

This allows for us to automatically bootstrap a cluster of nodes after
'n' number of server nodes join. All servers must have the same 'n' set, or
they will fail to join the cluster; all servers will not join the peer set
until they hit 'n' server nodes.

If the raft commit index is not empty, '-expect=n' does nothing because it
thinks you've already bootstrapped.

Signed-off-by: Robert Xu <robxu9@gmail.com>

command/agent/agent.go

@@ -2,15 +2,16 @@ package agent
 
 import (
 	"fmt"
-	"github.com/hashicorp/consul/consul"
-	"github.com/hashicorp/consul/consul/structs"
-	"github.com/hashicorp/serf/serf"
 	"io"
 	"log"
 	"net"
 	"os"
 	"strconv"
 	"sync"
+
+	"github.com/hashicorp/consul/consul"
+	"github.com/hashicorp/consul/consul/structs"
+	"github.com/hashicorp/serf/serf"
 )
 
 /*
@@ -171,6 +172,9 @@ func (a *Agent) consulConfig() *consul.Config {
 	if a.config.Bootstrap {
 		base.Bootstrap = true
 	}
+	if a.config.Expect != 0 {
+		base.Expect = a.config.Expect
+	}
 	if a.config.Protocol > 0 {
 		base.ProtocolVersion = uint8(a.config.Protocol)
 	}

command/agent/command.go

@@ -3,10 +3,6 @@ package agent
 import (
 	"flag"
 	"fmt"
-	"github.com/armon/go-metrics"
-	"github.com/hashicorp/go-syslog"
-	"github.com/hashicorp/logutils"
-	"github.com/mitchellh/cli"
 	"io"
 	"net"
 	"os"
@@ -16,6 +12,11 @@ import (
 	"strings"
 	"syscall"
 	"time"
+
+	"github.com/armon/go-metrics"
+	"github.com/hashicorp/go-syslog"
+	"github.com/hashicorp/logutils"
+	"github.com/mitchellh/cli"
 )
 
 // gracefulTimeout controls how long we wait before forcefully terminating
@@ -62,6 +63,7 @@ func (c *Command) readConfig() *Config {
 
 	cmdFlags.BoolVar(&cmdConfig.Server, "server", false, "run agent as server")
 	cmdFlags.BoolVar(&cmdConfig.Bootstrap, "bootstrap", false, "enable server bootstrap mode")
+	cmdFlags.IntVar(&cmdConfig.Expect, "expect", 0, "enable automatic bootstrap via expect mode")
 
 	cmdFlags.StringVar(&cmdConfig.ClientAddr, "client", "", "address to bind client listeners to (DNS, HTTP, RPC)")
 	cmdFlags.StringVar(&cmdConfig.BindAddr, "bind", "", "address to bind server listeners to")
@@ -127,6 +129,30 @@ func (c *Command) readConfig() *Config {
 		return nil
 	}
 
+	// Expect can only work when acting as a server
+	if config.Expect != 0 && !config.Server {
+		c.Ui.Error("Expect mode cannot be enabled when server mode is not enabled")
+		return nil
+	}
+
+	// Expect & Bootstrap are mutually exclusive
+	if config.Expect != 0 && config.Bootstrap {
+		c.Ui.Error("Expect mode and Bootstrap mode are mutually exclusive")
+		return nil
+	}
+
+	// Warn if we are in expect mode
+	if config.Expect != 0 {
+		if config.Expect == 1 {
+			// just use bootstrap mode
+			c.Ui.Error("WARNING: Expect Mode is specified as 1; this is the same as Bootstrap mode.")
+			config.Expect = 0
+			config.Bootstrap = true
+		} else {
+			c.Ui.Error(fmt.Sprintf("WARNING: Expect Mode enabled, looking for %v servers!", config.Expect))
+		}
+	}
+
 	// Warn if we are in bootstrap mode
 	if config.Bootstrap {
 		c.Ui.Error("WARNING: Bootstrap mode enabled! Do not enable unless necessary")
@@ -524,6 +550,7 @@ Options:
                            order.
   -data-dir=path           Path to a data directory to store agent state
   -dc=east-aws             Datacenter of the agent
+  -expect=0                Sets server to expect bootstrap mode.
   -join=1.2.3.4            Address of an agent to join at start time.
                            Can be specified multiple times.
   -log-level=info          Log level of the agent.

command/agent/config.go

@@ -4,8 +4,6 @@ import (
 	"encoding/base64"
 	"encoding/json"
 	"fmt"
-	"github.com/hashicorp/consul/consul"
-	"github.com/mitchellh/mapstructure"
 	"io"
 	"net"
 	"os"
@@ -13,6 +11,9 @@ import (
 	"sort"
 	"strings"
 	"time"
+
+	"github.com/hashicorp/consul/consul"
+	"github.com/mitchellh/mapstructure"
 )
 
 // Ports is used to simplify the configuration by
@@ -64,6 +65,10 @@ type Config struct {
 	// permits that node to elect itself leader
 	Bootstrap bool `mapstructure:"bootstrap"`
 
+	// Expect tries to automatically bootstrap the Consul cluster,
+	// by witholding peers until enough servers join.
+	Expect int `mapstructure:"expect"`
+
 	// Server controls if this agent acts like a Consul server,
 	// or merely as a client. Servers have more state, take part
 	// in leader election, etc.
@@ -219,6 +224,7 @@ type dirEnts []os.FileInfo
 func DefaultConfig() *Config {
 	return &Config{
 		Bootstrap:  false,
+		Expect:     0,
 		Server:     false,
 		Datacenter: consul.DefaultDC,
 		Domain:     "consul.",
@@ -449,6 +455,9 @@ func MergeConfig(a, b *Config) *Config {
 	if b.Bootstrap {
 		result.Bootstrap = true
 	}
+	if b.Expect != 0 {
+		result.Expect = b.Expect
+	}
 	if b.Datacenter != "" {
 		result.Datacenter = b.Datacenter
 	}

command/agent/config_test.go

@@ -93,6 +93,21 @@ func TestDecodeConfig(t *testing.T) {
 		t.Fatalf("bad: %#v", config)
 	}
 
+	// Expect bootstrap
+	input = `{"server": true, "expect": 3}`
+	config, err = DecodeConfig(bytes.NewReader([]byte(input)))
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if !config.Server {
+		t.Fatalf("bad: %#v", config)
+	}
+
+	if config.Expect != 3 {
+		t.Fatalf("bad: %#v", config)
+	}
+
 	// DNS setup
 	input = `{"ports": {"dns": 8500}, "recursor": "8.8.8.8", "domain": "foobar"}`
 	config, err = DecodeConfig(bytes.NewReader([]byte(input)))
@@ -426,6 +441,7 @@ func TestDecodeConfig_Check(t *testing.T) {
 func TestMergeConfig(t *testing.T) {
 	a := &Config{
 		Bootstrap:              false,
+		Expect:                 0,
 		Datacenter:             "dc1",
 		DataDir:                "/tmp/foo",
 		DNSRecursor:            "127.0.0.1:1001",
@@ -444,6 +460,7 @@ func TestMergeConfig(t *testing.T) {
 
 	b := &Config{
 		Bootstrap:   true,
+		Expect:      3,
 		Datacenter:  "dc2",
 		DataDir:     "/tmp/bar",
 		DNSRecursor: "127.0.0.2:1001",

consul/config.go

@@ -44,6 +44,11 @@ type Config struct {
 	// other nodes being present
 	Bootstrap bool
 
+	// Expect mode is used to automatically bring up a collection of
+	// Consul servers. This can be used to automatically bring up a collection
+	// of nodes.
+	Expect int
+
 	// Datacenter is the datacenter this Consul server represents
 	Datacenter string
 

consul/leader.go

@@ -1,13 +1,14 @@
 package consul
 
 import (
+	"net"
+	"strconv"
+	"time"
+
 	"github.com/armon/go-metrics"
 	"github.com/hashicorp/consul/consul/structs"
 	"github.com/hashicorp/raft"
 	"github.com/hashicorp/serf/serf"
-	"net"
-	"strconv"
-	"time"
 )
 
 const (
@@ -368,6 +369,57 @@ func (s *Server) joinConsulServer(m serf.Member, parts *serverParts) error {
 		}
 	}
 
+	// Or, check for possibility that expect is not the same.
+	if parts.Expect != 0 {
+		members := s.serfLAN.Members()
+		for _, member := range members {
+			valid, p := isConsulServer(member)
+			if valid && member.Name != m.Name && p.Expect != parts.Expect {
+				s.logger.Printf("[ERR] consul: '%v' and '%v' have different expect values. All expect nodes should have the same value, not adding Raft peer.", m.Name, member.Name)
+				return nil
+			}
+		}
+	}
+
+	// If we're not a bootstrapped server, we're expecting servers,
+	// and our raft index is zero, try to auto bootstrap.
+	if !s.config.Bootstrap && s.config.Expect != 0 {
+		if index, _ := s.raftStore.LastIndex(); index == 0 {
+			// do not do standard op and add peer... yet
+			count := 0
+			members := s.serfLAN.Members()
+			for _, member := range members {
+				valid, p := isConsulServer(member)
+				if valid && member.Name != m.Name && p.Expect == parts.Expect {
+					count++
+					if count >= s.config.Expect {
+						break
+					}
+				}
+			}
+
+			if count >= s.config.Expect {
+				// we've met expected limit - add servers
+				s.config.RaftConfig.EnableSingleNode = false
+				for _, member := range members {
+					valid, p := isConsulServer(member)
+					if valid && member.Name != m.Name && p.Expect != parts.Expect {
+						addAddr := &net.TCPAddr{IP: member.Addr, Port: p.Port}
+						future := s.raft.AddPeer(addAddr)
+
+						if err := future.Error(); err != nil && err != raft.ErrKnownPeer {
+							s.logger.Printf("[ERR] consul: failed to add raft peer: %v", err)
+							// hmm....
+						}
+					}
+				}
+			} else {
+				// not enough servers yet
+				return nil
+			}
+		}
+	}
+
 	// Attempt to add as a peer
 	var addr net.Addr = &net.TCPAddr{IP: m.Addr, Port: parts.Port}
 	future := s.raft.AddPeer(addr)

consul/server.go

@@ -4,9 +4,6 @@ import (
 	"crypto/tls"
 	"errors"
 	"fmt"
-	"github.com/hashicorp/raft"
-	"github.com/hashicorp/raft-mdb"
-	"github.com/hashicorp/serf/serf"
 	"log"
 	"net"
 	"net/rpc"
@@ -17,6 +14,10 @@ import (
 	"strconv"
 	"sync"
 	"time"
+
+	"github.com/hashicorp/raft"
+	"github.com/hashicorp/raft-mdb"
+	"github.com/hashicorp/serf/serf"
 )
 
 // These are the protocol versions that Consul can _understand_. These are
@@ -233,6 +234,7 @@ func (s *Server) setupSerf(conf *serf.Config, ch chan serf.Event, path string, w
 	if s.config.Bootstrap {
 		conf.Tags["bootstrap"] = "1"
 	}
+	conf.Tags["expect"] = fmt.Sprintf("%d", s.config.Expect)
 	conf.MemberlistConfig.LogOutput = s.config.LogOutput
 	conf.LogOutput = s.config.LogOutput
 	conf.EventCh = ch
@@ -252,8 +254,8 @@ func (s *Server) setupSerf(conf *serf.Config, ch chan serf.Event, path string, w
 
 // setupRaft is used to setup and initialize Raft
 func (s *Server) setupRaft() error {
-	// If we are in bootstrap mode, enable a single node cluster
-	if s.config.Bootstrap {
+	// If we are in bootstrap or expect mode, enable a single node cluster
+	if s.config.Bootstrap || s.config.Expect != 0 {
 		s.config.RaftConfig.EnableSingleNode = true
 	}
 

consul/server_test.go

@@ -3,12 +3,13 @@ package consul
 import (
 	"errors"
 	"fmt"
-	"github.com/hashicorp/consul/testutil"
 	"io/ioutil"
 	"net"
 	"os"
 	"testing"
 	"time"
+
+	"github.com/hashicorp/consul/testutil"
 )
 
 var nextPort = 15000
@@ -87,6 +88,19 @@ func testServerDCBootstrap(t *testing.T, dc string, bootstrap bool) (string, *Se
 	return dir, server
 }
 
+func testServerDCExpect(t *testing.T, dc string, expect int) (string, *Server) {
+	name := fmt.Sprintf("Node %d", getPort())
+	dir, config := testServerConfig(t, name)
+	config.Datacenter = dc
+	config.Bootstrap = false
+	config.Expect = expect
+	server, err := NewServer(config)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	return dir, server
+}
+
 func TestServer_StartStop(t *testing.T) {
 	dir := tmpDir(t)
 	defer os.RemoveAll(dir)
@@ -304,3 +318,145 @@ func TestServer_JoinLAN_TLS(t *testing.T) {
 		t.Fatalf("no peer established")
 	})
 }
+
+func TestServer_Expect(t *testing.T) {
+	// all test servers should be in expect=3 mode
+	dir1, s1 := testServerDCExpect(t, "dc1", 3)
+	defer os.RemoveAll(dir1)
+	defer s1.Shutdown()
+
+	dir2, s2 := testServerDCExpect(t, "dc1", 3)
+	defer os.RemoveAll(dir2)
+	defer s2.Shutdown()
+
+	dir3, s3 := testServerDCExpect(t, "dc1", 3)
+	defer os.RemoveAll(dir3)
+	defer s3.Shutdown()
+
+	// Try to join
+	addr := fmt.Sprintf("127.0.0.1:%d",
+		s1.config.SerfLANConfig.MemberlistConfig.BindPort)
+	if _, err := s2.JoinLAN([]string{addr}); err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	var p1 []net.Addr
+	var p2 []net.Addr
+
+	// should have no peers yet
+	testutil.WaitForResult(func() (bool, error) {
+		p1, _ = s1.raftPeers.Peers()
+		return len(p1) == 0, errors.New(fmt.Sprintf("%v", p1))
+	}, func(err error) {
+		t.Fatalf("should have 0 peers: %v", err)
+	})
+
+	testutil.WaitForResult(func() (bool, error) {
+		p2, _ = s2.raftPeers.Peers()
+		return len(p2) == 0, errors.New(fmt.Sprintf("%v", p1))
+	}, func(err error) {
+		t.Fatalf("should have 0 peers: %v", err)
+	})
+
+	// join the third node
+	if _, err := s3.JoinLAN([]string{addr}); err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	var p3 []net.Addr
+
+	// should now have all three peers
+	testutil.WaitForResult(func() (bool, error) {
+		p1, _ = s1.raftPeers.Peers()
+		return len(p1) == 3, errors.New(fmt.Sprintf("%v", p1))
+	}, func(err error) {
+		t.Fatalf("should have 3 peers: %v", err)
+	})
+
+	testutil.WaitForResult(func() (bool, error) {
+		p2, _ = s2.raftPeers.Peers()
+		return len(p2) == 3, errors.New(fmt.Sprintf("%v", p1))
+	}, func(err error) {
+		t.Fatalf("should have 3 peers: %v", err)
+	})
+
+	testutil.WaitForResult(func() (bool, error) {
+		p3, _ = s3.raftPeers.Peers()
+		return len(p3) == 3, errors.New(fmt.Sprintf("%v", p1))
+	}, func(err error) {
+		t.Fatalf("should have 3 peers: %v", err)
+	})
+
+}
+
+func TestServer_BadExpect(t *testing.T) {
+	// this one is in expect=3 mode
+	dir1, s1 := testServerDCExpect(t, "dc1", 3)
+	defer os.RemoveAll(dir1)
+	defer s1.Shutdown()
+
+	// this one is in expect=2 mode
+	dir2, s2 := testServerDCExpect(t, "dc1", 2)
+	defer os.RemoveAll(dir2)
+	defer s2.Shutdown()
+
+	// and this one is in expect=3 mode
+	dir3, s3 := testServerDCExpect(t, "dc1", 3)
+	defer os.RemoveAll(dir3)
+	defer s3.Shutdown()
+
+	// Try to join
+	addr := fmt.Sprintf("127.0.0.1:%d",
+		s1.config.SerfLANConfig.MemberlistConfig.BindPort)
+	if _, err := s2.JoinLAN([]string{addr}); err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	var p1 []net.Addr
+	var p2 []net.Addr
+
+	// should have no peers yet
+	testutil.WaitForResult(func() (bool, error) {
+		p1, _ = s1.raftPeers.Peers()
+		return len(p1) == 0, errors.New(fmt.Sprintf("%v", p1))
+	}, func(err error) {
+		t.Fatalf("should have 0 peers: %v", err)
+	})
+
+	testutil.WaitForResult(func() (bool, error) {
+		p2, _ = s2.raftPeers.Peers()
+		return len(p2) == 0, errors.New(fmt.Sprintf("%v", p1))
+	}, func(err error) {
+		t.Fatalf("should have 0 peers: %v", err)
+	})
+
+	// join the third node
+	if _, err := s3.JoinLAN([]string{addr}); err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	var p3 []net.Addr
+
+	// should still have no peers (because s2 is in expect=2 mode)
+	testutil.WaitForResult(func() (bool, error) {
+		p1, _ = s1.raftPeers.Peers()
+		return len(p1) == 0, errors.New(fmt.Sprintf("%v", p1))
+	}, func(err error) {
+		t.Fatalf("should have 0 peers: %v", err)
+	})
+
+	testutil.WaitForResult(func() (bool, error) {
+		p2, _ = s2.raftPeers.Peers()
+		return len(p2) == 0, errors.New(fmt.Sprintf("%v", p1))
+	}, func(err error) {
+		t.Fatalf("should have 0 peers: %v", err)
+	})
+
+	testutil.WaitForResult(func() (bool, error) {
+		p3, _ = s3.raftPeers.Peers()
+		return len(p3) == 0, errors.New(fmt.Sprintf("%v", p1))
+	}, func(err error) {
+		t.Fatalf("should have 0 peers: %v", err)
+	})
+
+}

consul/util.go

@@ -4,12 +4,13 @@ import (
 	crand "crypto/rand"
 	"encoding/binary"
 	"fmt"
-	"github.com/hashicorp/serf/serf"
 	"net"
 	"os"
 	"path/filepath"
 	"runtime"
 	"strconv"
+
+	"github.com/hashicorp/serf/serf"
 )
 
 /*
@@ -26,6 +27,7 @@ type serverParts struct {
 	Datacenter string
 	Port       int
 	Bootstrap  bool
+	Expect     int
 	Version    int
 	Addr       net.Addr
 }
@@ -84,6 +86,12 @@ func isConsulServer(m serf.Member) (bool, *serverParts) {
 	datacenter := m.Tags["dc"]
 	_, bootstrap := m.Tags["bootstrap"]
 
+	expect_str := m.Tags["expect"]
+	expect, err := strconv.Atoi(expect_str)
+	if err != nil {
+		return false, nil
+	}
+
 	port_str := m.Tags["port"]
 	port, err := strconv.Atoi(port_str)
 	if err != nil {
@@ -103,6 +111,7 @@ func isConsulServer(m serf.Member) (bool, *serverParts) {
 		Datacenter: datacenter,
 		Port:       port,
 		Bootstrap:  bootstrap,
+		Expect:     expect,
 		Addr:       addr,
 		Version:    vsn,
 	}

consul/util_test.go

@@ -1,10 +1,11 @@
 package consul
 
 import (
-	"github.com/hashicorp/serf/serf"
 	"net"
 	"regexp"
 	"testing"
+
+	"github.com/hashicorp/serf/serf"
 )
 
 func TestStrContains(t *testing.T) {
@@ -40,10 +41,11 @@ func TestIsConsulServer(t *testing.T) {
 		Name: "foo",
 		Addr: net.IP([]byte{127, 0, 0, 1}),
 		Tags: map[string]string{
-			"role": "consul",
-			"dc":   "east-aws",
-			"port": "10000",
-			"vsn":  "1",
+			"expect": "0",
+			"role":   "consul",
+			"dc":     "east-aws",
+			"port":   "10000",
+			"vsn":    "1",
 		},
 	}
 	valid, parts := isConsulServer(m)
@@ -56,6 +58,9 @@ func TestIsConsulServer(t *testing.T) {
 	if parts.Bootstrap {
 		t.Fatalf("unexpected bootstrap")
 	}
+	if parts.Expect != 0 {
+		t.Fatalf("bad: %v", parts.Expect)
+	}
 	m.Tags["bootstrap"] = "1"
 	valid, parts = isConsulServer(m)
 	if !valid || !parts.Bootstrap {
@@ -67,6 +72,12 @@ func TestIsConsulServer(t *testing.T) {
 	if parts.Version != 1 {
 		t.Fatalf("bad: %v", parts)
 	}
+	m.Tags["expect"] = "3"
+	delete(m.Tags, "bootstrap")
+	valid, parts = isConsulServer(m)
+	if !valid || parts.Expect != 3 {
+		t.Fatalf("bad: %v", parts.Expect)
+	}
 }
 
 func TestIsConsulNode(t *testing.T) {