better error handling around Scaling->Max

CHANGELOG.md

@@ -22,6 +22,7 @@ IMPROVEMENTS:
 
 * core: Support for persisting previous task group counts when updating a job [[GH-8168](https://github.com/hashicorp/nomad/issues/8168)]
 * core: Block Job.Scale actions when the job is under active deployment [[GH-8187](https://github.com/hashicorp/nomad/issues/8187)]
+* api: Better error messages around Scaling->Max [[GH-8360](https://github.com/hashicorp/nomad/issues/8360)]
 * api: Persist previous count with scaling events [[GH-8167](https://github.com/hashicorp/nomad/issues/8167)]
 * api: Support querying for jobs and allocations across all namespaces [[GH-8192](https://github.com/hashicorp/nomad/issues/8192)]
 * api: New `/agent/host` endpoint returns diagnostic information about the host [[GH-8325](https://github.com/hashicorp/nomad/pull/8325)]

api/scaling.go

@@ -56,7 +56,7 @@ type ScalingPolicy struct {
 	Namespace   string
 	Target      map[string]string
 	Min         *int64
-	Max         int64
+	Max         *int64
 	Policy      map[string]interface{}
 	Enabled     *bool
 	CreateIndex uint64

api/scaling_test.go

@@ -23,7 +23,7 @@ func TestScalingPolicies_ListPolicies(t *testing.T) {
 	// Register a job with a scaling policy
 	job := testJob()
 	job.TaskGroups[0].Scaling = &ScalingPolicy{
-		Max: 100,
+		Max: int64ToPtr(100),
 	}
 	_, _, err = jobs.Register(job, nil)
 	require.NoError(err)
@@ -75,7 +75,7 @@ func TestScalingPolicies_GetPolicy(t *testing.T) {
 	policy := &ScalingPolicy{
 		Enabled: boolToPtr(true),
 		Min:     int64ToPtr(1),
-		Max:     1,
+		Max:     int64ToPtr(1),
 		Policy: map[string]interface{}{
 			"key": "value",
 		},

api/tasks_test.go

@@ -444,7 +444,7 @@ func TestTaskGroup_Canonicalize_Scaling(t *testing.T) {
 		Count: nil,
 		Scaling: &ScalingPolicy{
 			Min:         nil,
-			Max:         10,
+			Max:         int64ToPtr(10),
 			Policy:      nil,
 			Enabled:     nil,
 			CreateIndex: 0,

api/util_test.go

@@ -53,7 +53,7 @@ func testJobWithScalingPolicy() *Job {
 	job.TaskGroups[0].Scaling = &ScalingPolicy{
 		Policy:  map[string]interface{}{},
 		Min:     int64ToPtr(1),
-		Max:     1,
+		Max:     int64ToPtr(1),
 		Enabled: boolToPtr(true),
 	}
 	return job

command/agent/scaling_endpoint.go

@@ -78,10 +78,15 @@ func (s *HTTPServer) scalingPolicyQuery(resp http.ResponseWriter, req *http.Requ
 func ApiScalingPolicyToStructs(count int, ap *api.ScalingPolicy) *structs.ScalingPolicy {
 	p := structs.ScalingPolicy{
 		Enabled: *ap.Enabled,
-		Max:     ap.Max,
 		Policy:  ap.Policy,
 		Target:  map[string]string{},
 	}
+	if ap.Max != nil {
+		p.Max = *ap.Max
+	} else {
+		// catch this in Validate
+		p.Max = -1
+	}
 	if ap.Min != nil {
 		p.Min = *ap.Min
 	} else {

jobspec/parse_group.go

@@ -364,6 +364,9 @@ func parseScalingPolicy(out **api.ScalingPolicy, list *ast.ObjectList) error {
 	if err := dec.Decode(m); err != nil {
 		return err
 	}
+	if result.Max == nil {
+		return fmt.Errorf("missing 'max'")
+	}
 
 	// If we have policy, then parse that
 	if o := listVal.Filter("policy"); len(o.Items) > 0 {

jobspec/parse_test.go

@@ -1320,7 +1320,7 @@ func TestParse(t *testing.T) {
 						Name: helper.StringToPtr("group"),
 						Scaling: &api.ScalingPolicy{
 							Min: helper.Int64ToPtr(5),
-							Max: 100,
+							Max: helper.Int64ToPtr(100),
 							Policy: map[string]interface{}{
 								"foo": "bar",
 								"b":   true,
@@ -1345,7 +1345,7 @@ func TestParse(t *testing.T) {
 						Name: helper.StringToPtr("group"),
 						Scaling: &api.ScalingPolicy{
 							Min:     nil,
-							Max:     0,
+							Max:     helper.Int64ToPtr(10),
 							Policy:  nil,
 							Enabled: nil,
 						},
@@ -1355,6 +1355,12 @@ func TestParse(t *testing.T) {
 			false,
 		},
 
+		{
+			"tg-scaling-policy-missing-max.hcl",
+			nil,
+			true,
+		},
+
 		{
 			"tg-scaling-policy-multi-policy.hcl",
 			nil,

jobspec/test-fixtures/tg-scaling-policy-minimal.hcl

@@ -1,5 +1,7 @@
 job "elastic" {
   group "group" {
-    scaling {}
+    scaling {
+      max = 10
+    }
   }
 }

jobspec/test-fixtures/tg-scaling-policy-missing-max.hcl

@@ -0,0 +1,7 @@
+job "elastic" {
+  group "group" {
+    scaling {
+      // required: max = ...
+    }
+  }
+}

nomad/structs/structs.go

@@ -5948,21 +5948,26 @@ func (tg *TaskGroup) validateScalingPolicy(j *Job) error {
 
 	var mErr multierror.Error
 
-	if tg.Scaling.Min > tg.Scaling.Max {
+	// was invalid or not specified; don't bother testing anything else involving max
+	if tg.Scaling.Max < 0 {
 		mErr.Errors = append(mErr.Errors,
-			fmt.Errorf("Scaling policy invalid: maximum count must not be less than minimum count"))
+			fmt.Errorf("Scaling policy invalid: maximum count must be specified and non-negative"))
+	} else {
+		if tg.Scaling.Max < tg.Scaling.Min {
+			mErr.Errors = append(mErr.Errors,
+				fmt.Errorf("Scaling policy invalid: maximum count must not be less than minimum count"))
+		}
+		if tg.Scaling.Max < int64(tg.Count) {
+			mErr.Errors = append(mErr.Errors,
+				fmt.Errorf("Scaling policy invalid: task group count must not be greater than maximum count in scaling policy"))
+		}
 	}
 
-	if int64(tg.Count) < tg.Scaling.Min && !(j.IsMultiregion() && tg.Count == 0) {
+	if int64(tg.Count) < tg.Scaling.Min && !(j.IsMultiregion() && tg.Count == 0 && j.Region == "global") {
 		mErr.Errors = append(mErr.Errors,
 			fmt.Errorf("Scaling policy invalid: task group count must not be less than minimum count in scaling policy"))
 	}
 
-	if tg.Scaling.Max < int64(tg.Count) {
-		mErr.Errors = append(mErr.Errors,
-			fmt.Errorf("Scaling policy invalid: task group count must not be greater than maximum count in scaling policy"))
-	}
-
 	return mErr.ErrorOrNil()
 }
 

website/pages/docs/job-specification/group.mdx

@@ -36,8 +36,10 @@ job "docs" {
   node attribute or metadata. See the
   [Nomad spread reference](/docs/job-specification/spread) for more details.
 
-- `count` `(int: 1)` - Specifies the number of the task groups that should
-  be running under this group. This value must be non-negative.
+- `count` `(int)` - Specifies the number of instances that should be running
+  under for this group. This value must be non-negative. This defaults to the
+  `min` value specified in the [`scaling`](/docs/job-specification/scaling)
+  block, if present; otherwise, this defaults to `1`.
 
 - `ephemeral_disk` <code>([EphemeralDisk][]: nil)</code> - Specifies the
   ephemeral disk requirements of the group. Ephemeral disks can be marked as