nomad: create system scheduler as needed

nomad/server.go

@@ -99,10 +99,6 @@ type Server struct {
 	// plans that are waiting to be assessed by the leader
 	planQueue *PlanQueue
 
-	// systemSched is the special system scheduler used for
-	// various maintanence and book keeping.
-	systemSched *SystemScheduler
-
 	left         bool
 	shutdown     bool
 	shutdownCh   chan struct{}
@@ -161,9 +157,6 @@ func NewServer(config *Config) (*Server, error) {
 		shutdownCh:  make(chan struct{}),
 	}
 
-	// Create the system scheduler
-	s.systemSched = &SystemScheduler{srv: s}
-
 	// Initialize the RPC layer
 	// TODO: TLS...
 	if err := s.setupRPC(nil); err != nil {

nomad/system_sched.go

@@ -0,0 +1,28 @@
+package nomad
+
+import (
+	"github.com/hashicorp/nomad/nomad/structs"
+	"github.com/hashicorp/nomad/scheduler"
+)
+
+// SystemScheduler is a special "scheduler" that is registered
+// as "system". It is used to run various administrative work
+// across the cluster.
+type SystemScheduler struct {
+	srv  *Server
+	snap *StateSnapshot
+}
+
+// NewSystemScheduler is used to return a new system scheduler instance
+func NewSystemScheduler(srv *Server, snap *StateSnapshot) scheduler.Scheduler {
+	s := &SystemScheduler{
+		srv:  srv,
+		snap: snap,
+	}
+	return s
+}
+
+// Process is used to implement the scheduler.Scheduler interface
+func (s *SystemScheduler) Process(*structs.Evaluation) error {
+	return nil
+}

nomad/worker.go

@@ -193,7 +193,7 @@ func (w *Worker) invokeScheduler(eval *structs.Evaluation) error {
 	// Create the scheduler, or use the special system scheduler
 	var sched scheduler.Scheduler
 	if eval.Type == structs.JobTypeSystem {
-		sched = w.srv.systemSched
+		sched = NewSystemScheduler(w.srv, snap)
 	} else {
 		sched, err = scheduler.NewScheduler(eval.Type, snap, w)
 		if err != nil {