final review comments.

command/monitor.go

@@ -186,6 +186,9 @@ func (m *monitor) monitor(evalID string) int {
 	// Add the initial pending state
 	m.update(newEvalState())
 
+	m.ui.Info(fmt.Sprintf("%s: Monitoring evaluation %q",
+		formatTime(time.Now()), limit(evalID, m.length)))
+
 	for {
 		// Query the evaluation
 		eval, _, err := m.client.Evaluations().Info(evalID, nil)
@@ -194,9 +197,6 @@ func (m *monitor) monitor(evalID string) int {
 			return 1
 		}
 
-		m.ui.Info(fmt.Sprintf("%s: Monitoring evaluation %q",
-			formatTime(time.Now()), limit(eval.ID, m.length)))
-
 		// Create the new eval state.
 		state := newEvalState()
 		state.status = eval.Status

command/operator_scheduler_get_config.go

@@ -83,6 +83,7 @@ func (o *OperatorSchedulerGetConfig) Run(args []string) int {
 		fmt.Sprintf("Preemption Service Scheduler|%v", schedConfig.PreemptionConfig.ServiceSchedulerEnabled),
 		fmt.Sprintf("Preemption Batch Scheduler|%v", schedConfig.PreemptionConfig.BatchSchedulerEnabled),
 		fmt.Sprintf("Preemption SysBatch Scheduler|%v", schedConfig.PreemptionConfig.SysBatchSchedulerEnabled),
+		fmt.Sprintf("Modify Index|%v", resp.SchedulerConfig.ModifyIndex),
 	}))
 	return 0
 }

command/operator_scheduler_set_config.go

@@ -19,6 +19,7 @@ type OperatorSchedulerSetConfig struct {
 	// The scheduler configuration flags allow us to tell whether the user set
 	// a value or not. This means we can safely merge the current configuration
 	// with user supplied, selective updates.
+	checkIndex               string
 	schedulerAlgorithm       string
 	memoryOversubscription   flagHelper.BoolValue
 	rejectJobRegistration    flagHelper.BoolValue
@@ -32,6 +33,7 @@ type OperatorSchedulerSetConfig struct {
 func (o *OperatorSchedulerSetConfig) AutocompleteFlags() complete.Flags {
 	return mergeAutocompleteFlags(o.Meta.AutocompleteFlags(FlagSetClient),
 		complete.Flags{
+			"-check-index": complete.PredictAnything,
 			"-scheduler-algorithm": complete.PredictSet(
 				string(api.SchedulerAlgorithmBinpack),
 				string(api.SchedulerAlgorithmSpread),
@@ -58,6 +60,7 @@ func (o *OperatorSchedulerSetConfig) Run(args []string) int {
 	flags := o.Meta.FlagSet("set-config", FlagSetClient)
 	flags.Usage = func() { o.Ui.Output(o.Help()) }
 
+	flags.StringVar(&o.checkIndex, "check-index", "", "")
 	flags.StringVar(&o.schedulerAlgorithm, "scheduler-algorithm", "", "")
 	flags.Var(&o.memoryOversubscription, "memory-oversubscription", "")
 	flags.Var(&o.rejectJobRegistration, "reject-job-registration", "")
@@ -78,15 +81,37 @@ func (o *OperatorSchedulerSetConfig) Run(args []string) int {
 		return 1
 	}
 
+	// Convert the check index string and handle any errors before adding this
+	// to our request. This parsing handles empty values correctly.
+	checkIndex, _, err := parseCheckIndex(o.checkIndex)
+	if err != nil {
+		o.Ui.Error(fmt.Sprintf("Error parsing check-index value %q: %v", o.checkIndex, err))
+		return 1
+	}
+
 	// Fetch the current configuration. This will be used as a base to merge
 	// user configuration onto.
 	resp, _, err := client.Operator().SchedulerGetConfiguration(nil)
 	if err != nil {
 		o.Ui.Error(fmt.Sprintf("Error querying for scheduler configuration: %s", err))
 		return 1
 	}
+
+	if checkIndex > 0 && resp.SchedulerConfig.ModifyIndex != checkIndex {
+		errMsg := fmt.Sprintf("check-index %v does not match does not match current state value %v",
+			checkIndex, resp.SchedulerConfig.ModifyIndex)
+		o.Ui.Error(fmt.Sprintf("Error performing check index set: %s", errMsg))
+		return 1
+	}
+
 	schedulerConfig := resp.SchedulerConfig
 
+	// Overwrite the modification index if the user supplied one, otherwise we
+	// use what was included within the read response.
+	if checkIndex > 0 {
+		schedulerConfig.ModifyIndex = checkIndex
+	}
+
 	// Merge the current configuration with any values set by the operator.
 	if o.schedulerAlgorithm != "" {
 		schedulerConfig.SchedulerAlgorithm = api.SchedulerAlgorithm(o.schedulerAlgorithm)
@@ -132,6 +157,11 @@ General Options:
 
 Scheduler Set Config Options:
 
+  -check-index
+    If set, the scheduler config is only updated if the passed modify index
+    matches the current server side version. If a non-zero value is passed, it
+    ensures that the scheduler config is being updated from a known state.
+
   -scheduler-algorithm=["binpack"|"spread"]
     Specifies whether scheduler binpacks or spreads allocations on available
     nodes.

command/operator_scheduler_set_config_test.go

@@ -1,6 +1,7 @@
 package command
 
 import (
+	"strconv"
 	"testing"
 
 	"github.com/hashicorp/nomad/api"
@@ -74,6 +75,28 @@ func TestOperatorSchedulerSetConfig_Run(t *testing.T) {
 	// returned.
 	require.EqualValues(t, 1, c.Run([]string{"-address=" + addr, "-pause-evil-broker=true"}))
 	require.Contains(t, ui.OutputWriter.String(), "Usage: nomad operator scheduler set-config")
+	ui.ErrorWriter.Reset()
+	ui.OutputWriter.Reset()
+
+	// Try updating the config using an incorrect check-index value.
+	require.EqualValues(t, 1, c.Run([]string{
+		"-address=" + addr,
+		"-pause-eval-broker=false",
+		"-check-index=1000000",
+	}))
+	require.Contains(t, ui.ErrorWriter.String(), "check-index 1000000 does not match does not match current state")
+	ui.ErrorWriter.Reset()
+	ui.OutputWriter.Reset()
+
+	// Try updating the config using a correct check-index value.
+	require.EqualValues(t, 0, c.Run([]string{
+		"-address=" + addr,
+		"-pause-eval-broker=false",
+		"-check-index=" + strconv.FormatUint(modifiedConfig.SchedulerConfig.ModifyIndex, 10),
+	}))
+	require.Contains(t, ui.OutputWriter.String(), "Scheduler configuration updated!")
+	ui.ErrorWriter.Reset()
+	ui.OutputWriter.Reset()
 }
 
 func schedulerConfigEquals(t *testing.T, expected, actual *api.SchedulerConfiguration) {

website/content/docs/commands/operator/scheduler-get-config.mdx

@@ -35,12 +35,13 @@ Display the current scheduler configuration:
 
 ```shell-session
 $ nomad operator scheduler get-config
-Scheduler Algorithm          = binpack
-Memory Oversubscription      = false
-Reject Job Registration      = false
-Pause Eval Broker            = false
-Preemtion System Scheduler   = true
-Preemtion Service Scheduler  = false
-Preemtion Batch Scheduler    = false
-Preemtion SysBatch Scheduler = false
+Scheduler Algorithm           = binpack
+Memory Oversubscription       = false
+Reject Job Registration       = false
+Pause Eval Broker             = false
+Preemption System Scheduler   = true
+Preemption Service Scheduler  = false
+Preemption Batch Scheduler    = false
+Preemption SysBatch Scheduler = false
+Modify Index                  = 5
 ```

website/content/docs/commands/operator/scheduler-set-config.mdx

@@ -25,6 +25,11 @@ capability.
 
 ## Set Config Options
 
+- `-check-index` - If set, the scheduler config is only updated if the passed
+  modify index matches the current server side version. If a non-zero value is
+  passed, it ensures that the scheduler config is being updated from a known
+  state.
+
 - `-scheduler-algorithm` - Specifies whether scheduler binpacks or spreads
   allocations on available nodes. Must be one of `["binpack"|"spread"]`.
 
@@ -67,4 +72,11 @@ $ nomad operator scheduler set-config -scheduler-algorithm=spread
 Scheduler configuration updated!
 ```
 
+Modify the scheduler algorithm to spread using the check index flag:
+
+```shell-session
+$ nomad operator scheduler set-config -scheduler-algorithm=spread -check-index=5
+Scheduler configuration updated!
+```
+
 [`memory_max`]: /docs/job-specification/resources#memory_max