Add scheduler version enforcement

nomad/config.go

@@ -243,6 +243,7 @@ func DefaultConfig() *Config {
 		ConsulConfig:           config.DefaultConsulConfig(),
 		VaultConfig:            config.DefaultVaultConfig(),
 		RPCHoldTimeout:         5 * time.Second,
+		TLSConfig:              &config.TLSConfig{},
 	}
 
 	// Enable all known schedulers by default

nomad/eval_endpoint.go

@@ -8,6 +8,7 @@ import (
 	"github.com/hashicorp/go-memdb"
 	"github.com/hashicorp/nomad/nomad/structs"
 	"github.com/hashicorp/nomad/nomad/watch"
+	"github.com/hashicorp/nomad/scheduler"
 )
 
 const (
@@ -77,6 +78,12 @@ func (e *Eval) Dequeue(args *structs.EvalDequeueRequest,
 		return fmt.Errorf("dequeue requires at least one scheduler type")
 	}
 
+	// Check that there isn't a scheduler version mismatch
+	if args.SchedulerVersion != scheduler.SchedulerVersion {
+		return fmt.Errorf("dequeue disallowed: calling scheduler version is %d; leader version is %d",
+			args.SchedulerVersion, scheduler.SchedulerVersion)
+	}
+
 	// Ensure there is a default timeout
 	if args.Timeout <= 0 {
 		args.Timeout = DefaultDequeueTimeout

nomad/eval_endpoint_test.go

@@ -2,12 +2,14 @@ package nomad
 
 import (
 	"reflect"
+	"strings"
 	"testing"
 	"time"
 
 	"github.com/hashicorp/net-rpc-msgpackrpc"
 	"github.com/hashicorp/nomad/nomad/mock"
 	"github.com/hashicorp/nomad/nomad/structs"
+	"github.com/hashicorp/nomad/scheduler"
 	"github.com/hashicorp/nomad/testutil"
 )
 
@@ -142,8 +144,9 @@ func TestEvalEndpoint_Dequeue(t *testing.T) {
 
 	// Dequeue the eval
 	get := &structs.EvalDequeueRequest{
-		Schedulers:   defaultSched,
-		WriteRequest: structs.WriteRequest{Region: "global"},
+		Schedulers:       defaultSched,
+		SchedulerVersion: scheduler.SchedulerVersion,
+		WriteRequest:     structs.WriteRequest{Region: "global"},
 	}
 	var resp structs.EvalDequeueResponse
 	if err := msgpackrpc.CallWithCodec(codec, "Eval.Dequeue", get, &resp); err != nil {
@@ -164,6 +167,31 @@ func TestEvalEndpoint_Dequeue(t *testing.T) {
 	}
 }
 
+func TestEvalEndpoint_Dequeue_Version_Mismatch(t *testing.T) {
+	s1 := testServer(t, func(c *Config) {
+		c.NumSchedulers = 0 // Prevent automatic dequeue
+	})
+	defer s1.Shutdown()
+	codec := rpcClient(t, s1)
+	testutil.WaitForLeader(t, s1.RPC)
+
+	// Create the register request
+	eval1 := mock.Eval()
+	s1.evalBroker.Enqueue(eval1)
+
+	// Dequeue the eval
+	get := &structs.EvalDequeueRequest{
+		Schedulers:       defaultSched,
+		SchedulerVersion: 0,
+		WriteRequest:     structs.WriteRequest{Region: "global"},
+	}
+	var resp structs.EvalDequeueResponse
+	err := msgpackrpc.CallWithCodec(codec, "Eval.Dequeue", get, &resp)
+	if err == nil || !strings.Contains(err.Error(), "scheduler version is 0") {
+		t.Fatalf("err: %v", err)
+	}
+}
+
 func TestEvalEndpoint_Ack(t *testing.T) {
 	s1 := testServer(t, nil)
 	defer s1.Shutdown()

nomad/structs/structs.go

@@ -305,8 +305,9 @@ type EvalAckRequest struct {
 
 // EvalDequeueRequest is used when we want to dequeue an evaluation
 type EvalDequeueRequest struct {
-	Schedulers []string
-	Timeout    time.Duration
+	Schedulers       []string
+	Timeout          time.Duration
+	SchedulerVersion uint16
 	WriteRequest
 }
 

nomad/worker.go

@@ -27,6 +27,10 @@ const (
 	// the slower backoff
 	backoffLimitSlow = 10 * time.Second
 
+	// backoffSchedulerVersionMismatch is the backoff between retries when the
+	// scheduler version mismatches that of the leader.
+	backoffSchedulerVersionMismatch = 30 * time.Second
+
 	// dequeueTimeout is used to timeout an evaluation dequeue so that
 	// we can check if there is a shutdown event
 	dequeueTimeout = 500 * time.Millisecond
@@ -134,8 +138,9 @@ func (w *Worker) run() {
 func (w *Worker) dequeueEvaluation(timeout time.Duration) (*structs.Evaluation, string, bool) {
 	// Setup the request
 	req := structs.EvalDequeueRequest{
-		Schedulers: w.srv.config.EnabledSchedulers,
-		Timeout:    timeout,
+		Schedulers:       w.srv.config.EnabledSchedulers,
+		Timeout:          timeout,
+		SchedulerVersion: scheduler.SchedulerVersion,
 		WriteRequest: structs.WriteRequest{
 			Region: w.srv.config.Region,
 		},
@@ -154,7 +159,16 @@ REQ:
 		if time.Since(w.start) > dequeueErrGrace && !w.srv.IsShutdown() {
 			w.logger.Printf("[ERR] worker: failed to dequeue evaluation: %v", err)
 		}
-		if w.backoffErr(backoffBaselineSlow, backoffLimitSlow) {
+
+		// Adjust the backoff based on the error. If it is a scheduler version
+		// mismatch we increase the baseline.
+		base, limit := backoffBaselineFast, backoffLimitSlow
+		if strings.Contains(err.Error(), "calling scheduler version") {
+			base = backoffSchedulerVersionMismatch
+			limit = backoffSchedulerVersionMismatch
+		}
+
+		if w.backoffErr(base, limit) {
 			return nil, "", true
 		}
 		goto REQ

scheduler/scheduler.go

@@ -8,6 +8,14 @@ import (
 	"github.com/hashicorp/nomad/nomad/structs"
 )
 
+const (
+	// SchedulerVersion is the version of the scheduler. Changes to the
+	// scheduler that are incompatible with prior schedulers will increment this
+	// version. It is used to disallow dequeueing when the versions do not match
+	// across the leader and the dequeueing scheduler.
+	SchedulerVersion uint16 = 1
+)
+
 // BuiltinSchedulers contains the built in registered schedulers
 // which are available
 var BuiltinSchedulers = map[string]Factory{