Define BootstrapExepct as an int32 so it can be manipulated atomically.

command/agent/agent.go

@@ -11,6 +11,7 @@ import (
 	"strconv"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/hashicorp/nomad/client"
@@ -110,7 +111,7 @@ func (a *Agent) serverConfig() (*nomad.Config, error) {
 		if a.config.Server.BootstrapExpect == 1 {
 			conf.Bootstrap = true
 		} else {
-			conf.BootstrapExpect = a.config.Server.BootstrapExpect
+			atomic.StoreInt32(&conf.BootstrapExpect, int32(a.config.Server.BootstrapExpect))
 		}
 	}
 	if a.config.DataDir != "" {

nomad/config.go

@@ -52,8 +52,9 @@ type Config struct {
 
 	// BootstrapExpect mode is used to automatically bring up a
 	// collection of Nomad servers. This can be used to automatically
-	// bring up a collection of nodes.
-	BootstrapExpect int
+	// bring up a collection of nodes.  All operations on BootstrapExpect
+	// must be handled via `atomic.*Int32()` calls.
+	BootstrapExpect int32
 
 	// DataDir is the directory to store our state in
 	DataDir string

nomad/serf.go

@@ -1,6 +1,10 @@
 package nomad
 
-import "github.com/hashicorp/serf/serf"
+import (
+	"sync/atomic"
+
+	"github.com/hashicorp/serf/serf"
+)
 
 const (
 	// StatusReap is used to update the status of a node if we
@@ -66,7 +70,7 @@ func (s *Server) nodeJoin(me serf.MemberEvent) {
 		s.peerLock.Unlock()
 
 		// If we still expecting to bootstrap, may need to handle this
-		if s.config.BootstrapExpect != 0 {
+		if atomic.LoadInt32(&s.config.BootstrapExpect) != 0 {
 			s.maybeBootstrap()
 		}
 	}
@@ -91,7 +95,7 @@ func (s *Server) maybeBootstrap() {
 	// Bootstrap can only be done if there are no committed logs,
 	// remove our expectations of bootstrapping
 	if index != 0 {
-		s.config.BootstrapExpect = 0
+		atomic.StoreInt32(&s.config.BootstrapExpect, 0)
 		return
 	}
 
@@ -106,7 +110,7 @@ func (s *Server) maybeBootstrap() {
 		if p.Region != s.config.Region {
 			continue
 		}
-		if p.Expect != 0 && p.Expect != s.config.BootstrapExpect {
+		if p.Expect != 0 && p.Expect != int(atomic.LoadInt32(&s.config.BootstrapExpect)) {
 			s.logger.Printf("[ERR] nomad: peer %v has a conflicting expect value. All nodes should expect the same number.", member)
 			return
 		}
@@ -118,7 +122,7 @@ func (s *Server) maybeBootstrap() {
 	}
 
 	// Skip if we haven't met the minimum expect count
-	if len(addrs) < s.config.BootstrapExpect {
+	if len(addrs) < int(atomic.LoadInt32(&s.config.BootstrapExpect)) {
 		return
 	}
 
@@ -128,8 +132,8 @@ func (s *Server) maybeBootstrap() {
 		s.logger.Printf("[ERR] nomad: failed to bootstrap peers: %v", err)
 	}
 
-	// Bootstrapping comlete, don't enter this again
-	s.config.BootstrapExpect = 0
+	// Bootstrapping complete, don't enter this again
+	atomic.StoreInt32(&s.config.BootstrapExpect, 0)
 }
 
 // nodeFailed is used to handle fail events on the serf cluster

nomad/server.go

@@ -14,6 +14,7 @@ import (
 	"strconv"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	consulapi "github.com/hashicorp/consul/api"
@@ -651,8 +652,9 @@ func (s *Server) setupSerf(conf *serf.Config, ch chan serf.Event, path string) (
 	if s.config.Bootstrap || (s.config.DevMode && !s.config.DevDisableBootstrap) {
 		conf.Tags["bootstrap"] = "1"
 	}
-	if s.config.BootstrapExpect != 0 {
-		conf.Tags["expect"] = fmt.Sprintf("%d", s.config.BootstrapExpect)
+	bootstrapExpect := atomic.LoadInt32(&s.config.BootstrapExpect)
+	if bootstrapExpect != 0 {
+		conf.Tags["expect"] = fmt.Sprintf("%d", bootstrapExpect)
 	}
 	conf.MemberlistConfig.LogOutput = s.config.LogOutput
 	conf.LogOutput = s.config.LogOutput