nomad: disable service+batch preemption by default

Enterprise only.

Disable preemption for service and batch jobs by default.

Maintain backward compatibility in a x.y.Z release. Consider switching
the default for new clusters in the future.

command/agent/operator_endpoint_test.go

@@ -271,9 +271,11 @@ func TestOperator_SchedulerGetConfiguration(t *testing.T) {
 		require.Equal(200, resp.Code)
 		out, ok := obj.(structs.SchedulerConfigurationResponse)
 		require.True(ok)
+
+		// Only system jobs can preempt other jobs by default.
 		require.True(out.SchedulerConfig.PreemptionConfig.SystemSchedulerEnabled)
-		require.True(out.SchedulerConfig.PreemptionConfig.BatchSchedulerEnabled)
-		require.True(out.SchedulerConfig.PreemptionConfig.ServiceSchedulerEnabled)
+		require.False(out.SchedulerConfig.PreemptionConfig.BatchSchedulerEnabled)
+		require.False(out.SchedulerConfig.PreemptionConfig.ServiceSchedulerEnabled)
 	})
 }
 

internal/testing/apitests/operator_test.go

@@ -22,9 +22,17 @@ func TestAPI_OperatorSchedulerGetSetConfiguration(t *testing.T) {
 		r.Check(err)
 	})
 	require.True(config.SchedulerConfig.PreemptionConfig.SystemSchedulerEnabled)
+	require.False(config.SchedulerConfig.PreemptionConfig.BatchSchedulerEnabled)
+	require.False(config.SchedulerConfig.PreemptionConfig.ServiceSchedulerEnabled)
 
 	// Change a config setting
-	newConf := &api.SchedulerConfiguration{PreemptionConfig: api.PreemptionConfig{SystemSchedulerEnabled: false, BatchSchedulerEnabled: false}}
+	newConf := &api.SchedulerConfiguration{
+		PreemptionConfig: api.PreemptionConfig{
+			SystemSchedulerEnabled:  false,
+			BatchSchedulerEnabled:   true,
+			ServiceSchedulerEnabled: true,
+		},
+	}
 	resp, wm, err := operator.SchedulerSetConfiguration(newConf, nil)
 	require.Nil(err)
 	require.NotZero(wm.LastIndex)
@@ -33,7 +41,8 @@ func TestAPI_OperatorSchedulerGetSetConfiguration(t *testing.T) {
 	config, _, err = operator.SchedulerGetConfiguration(nil)
 	require.Nil(err)
 	require.False(config.SchedulerConfig.PreemptionConfig.SystemSchedulerEnabled)
-	require.False(config.SchedulerConfig.PreemptionConfig.BatchSchedulerEnabled)
+	require.True(config.SchedulerConfig.PreemptionConfig.BatchSchedulerEnabled)
+	require.True(config.SchedulerConfig.PreemptionConfig.ServiceSchedulerEnabled)
 }
 
 func TestAPI_OperatorSchedulerCASConfiguration(t *testing.T) {
@@ -50,11 +59,13 @@ func TestAPI_OperatorSchedulerCASConfiguration(t *testing.T) {
 		r.Check(err)
 	})
 	require.True(config.SchedulerConfig.PreemptionConfig.SystemSchedulerEnabled)
+	require.False(config.SchedulerConfig.PreemptionConfig.BatchSchedulerEnabled)
+	require.False(config.SchedulerConfig.PreemptionConfig.ServiceSchedulerEnabled)
 
 	// Pass an invalid ModifyIndex
 	{
 		newConf := &api.SchedulerConfiguration{
-			PreemptionConfig: api.PreemptionConfig{SystemSchedulerEnabled: false, BatchSchedulerEnabled: false},
+			PreemptionConfig: api.PreemptionConfig{SystemSchedulerEnabled: false, BatchSchedulerEnabled: true},
 			ModifyIndex:      config.SchedulerConfig.ModifyIndex - 1,
 		}
 		resp, wm, err := operator.SchedulerCASConfiguration(newConf, nil)
@@ -66,7 +77,7 @@ func TestAPI_OperatorSchedulerCASConfiguration(t *testing.T) {
 	// Pass a valid ModifyIndex
 	{
 		newConf := &api.SchedulerConfiguration{
-			PreemptionConfig: api.PreemptionConfig{SystemSchedulerEnabled: false, BatchSchedulerEnabled: false},
+			PreemptionConfig: api.PreemptionConfig{SystemSchedulerEnabled: false, BatchSchedulerEnabled: true},
 			ModifyIndex:      config.SchedulerConfig.ModifyIndex,
 		}
 		resp, wm, err := operator.SchedulerCASConfiguration(newConf, nil)
@@ -74,4 +85,10 @@ func TestAPI_OperatorSchedulerCASConfiguration(t *testing.T) {
 		require.NotZero(wm.LastIndex)
 		require.True(resp.Updated)
 	}
+
+	config, _, err := operator.SchedulerGetConfiguration(nil)
+	require.Nil(err)
+	require.False(config.SchedulerConfig.PreemptionConfig.SystemSchedulerEnabled)
+	require.True(config.SchedulerConfig.PreemptionConfig.BatchSchedulerEnabled)
+	require.False(config.SchedulerConfig.PreemptionConfig.ServiceSchedulerEnabled)
 }

nomad/leader.go

@@ -48,8 +48,8 @@ var minSchedulerConfigVersion = version.Must(version.NewVersion("0.9.0"))
 var defaultSchedulerConfig = &structs.SchedulerConfiguration{
 	PreemptionConfig: structs.PreemptionConfig{
 		SystemSchedulerEnabled:  true,
-		BatchSchedulerEnabled:   true,
-		ServiceSchedulerEnabled: true,
+		BatchSchedulerEnabled:   false,
+		ServiceSchedulerEnabled: false,
 	},
 }
 

website/source/api/operator.html.md

@@ -364,8 +364,8 @@ $ curl \
     "ModifyIndex": 5,
     "PreemptionConfig": {
       "SystemSchedulerEnabled": true,
-      "BatchSchedulerEnabled": true,
-      "ServiceSchedulerEnabled": true,
+      "BatchSchedulerEnabled": false,
+      "ServiceSchedulerEnabled": false
     }
   }
 }
@@ -381,10 +381,10 @@ $ curl \
   - `PreemptionConfig` `(PreemptionConfig)` - Options to enable preemption for various schedulers.
          - `SystemSchedulerEnabled` `(bool: true)` - Specifies whether preemption for system jobs is enabled. Note that
          this defaults to true.
-         - `BatchSchedulerEnabled` <sup>0.9.2</sup> `(bool: true)` (Enterprise Only) - Specifies whether preemption for batch jobs is enabled. Note that
-         this defaults to true.
-         - `ServiceSchedulerEnabled` <sup>0.9.2</sup> `(bool: true)` (Enterprise Only) - Specifies whether preemption for service jobs is enabled. Note that
-         this defaults to true.
+         - `BatchSchedulerEnabled` <sup>0.9.2</sup> `(bool: false)` (Enterprise Only) - Specifies whether preemption for batch jobs is enabled. Note that
+         this defaults to false and must be explicitly enabled.
+         - `ServiceSchedulerEnabled` <sup>0.9.2</sup> `(bool: false)` (Enterprise Only) - Specifies whether preemption for service jobs is enabled. Note that
+         this defaults to false and must be explicitly enabled.
   - `CreateIndex` - The Raft index at which the config was created.
   - `ModifyIndex` - The Raft index at which the config was modified.
 
@@ -415,9 +415,9 @@ The table below shows this endpoint's support for
 ```json
 {
   "PreemptionConfig": {
-    "SystemSchedulerEnabled": false,
+    "SystemSchedulerEnabled": true,
     "BatchSchedulerEnabled": false,
-    "ServiceSchedulerEnabled": true,
+    "ServiceSchedulerEnabled": true
   }
 }
 ```
@@ -425,7 +425,7 @@ The table below shows this endpoint's support for
 - `PreemptionConfig` `(PreemptionConfig)` - Options to enable preemption for various schedulers.
  - `SystemSchedulerEnabled` `(bool: true)` - Specifies whether preemption for system jobs is enabled. Note that
          if this is set to true, then system jobs can preempt any other jobs.
- - `BatchSchedulerEnabled` <sup>0.9.2</sup> `(bool: true)` (Enterprise Only) - Specifies whether preemption for batch jobs is enabled. Note that
+ - `BatchSchedulerEnabled` <sup>0.9.2</sup> `(bool: false)` (Enterprise Only) - Specifies whether preemption for batch jobs is enabled. Note that
          if this is set to true, then batch jobs can preempt any other jobs.
- - `ServiceSchedulerEnabled` <sup>0.9.2</sup> `(bool: true)` (Enterprise Only) - Specifies whether preemption for service jobs is enabled. Note that
+ - `ServiceSchedulerEnabled` <sup>0.9.2</sup> `(bool: false)` (Enterprise Only) - Specifies whether preemption for service jobs is enabled. Note that
          if this is set to true, then service jobs can preempt any other jobs.