spread scheduling algorithm

CHANGELOG.md

@@ -3,6 +3,10 @@
 FEATURES:
  * **Task dependencies UI**: task lifecycle charts and details
 
+IMPROVEMENTS:
+
+ * core: Allow spreading allocations as an alternative to binpacking [[GH-7810](https://github.com/hashicorp/nomad/issues/7810)]
+
 BUG FIXES:
 
  * api: autoscaling policies should not be returned for stopped jobs [[GH-7768](https://github.com/hashicorp/nomad/issues/7768)]

api/operator.go

@@ -112,7 +112,11 @@ func (op *Operator) RaftRemovePeerByID(id string, q *WriteOptions) error {
 	return nil
 }
 
+// SchedulerConfiguration is the config for controlling scheduler behavior
 type SchedulerConfiguration struct {
+	// SchedulerAlgorithm lets you select between available scheduling algorithms.
+	SchedulerAlgorithm SchedulerAlgorithm
+
 	// PreemptionConfig specifies whether to enable eviction of lower
 	// priority jobs to place higher priority jobs.
 	PreemptionConfig PreemptionConfig
@@ -140,6 +144,16 @@ type SchedulerSetConfigurationResponse struct {
 	WriteMeta
 }
 
+// SchedulerAlgorithm is an enum string that encapsulates the valid options for a
+// SchedulerConfiguration stanza's SchedulerAlgorithm. These modes will allow the
+// scheduler to be user-selectable.
+type SchedulerAlgorithm string
+
+const (
+	SchedulerAlgorithmBinpack SchedulerAlgorithm = "binpack"
+	SchedulerAlgorithmSpread  SchedulerAlgorithm = "spread"
+)
+
 // PreemptionConfig specifies whether preemption is enabled based on scheduler type
 type PreemptionConfig struct {
 	SystemSchedulerEnabled  bool

command/agent/agent_test.go

@@ -184,6 +184,7 @@ func TestAgent_ServerConfig_SchedulerFlags(t *testing.T) {
 			"default case",
 			nil,
 			structs.SchedulerConfiguration{
+				SchedulerAlgorithm: "binpack",
 				PreemptionConfig: structs.PreemptionConfig{
 					SystemSchedulerEnabled: true,
 				},

command/agent/command.go

@@ -377,6 +377,11 @@ func (c *Command) isValidConfig(config, cmdConfig *Config) bool {
 		c.Ui.Error("WARNING: Bootstrap mode enabled! Potentially unsafe operation.")
 	}
 
+	if err := config.Server.DefaultSchedulerConfig.Validate(); err != nil {
+		c.Ui.Error(err.Error())
+		return false
+	}
+
 	return true
 }
 

command/agent/config_parse_test.go

@@ -126,6 +126,7 @@ var basicConfig = &Config{
 			RetryMaxAttempts: 3,
 		},
 		DefaultSchedulerConfig: &structs.SchedulerConfiguration{
+			SchedulerAlgorithm: "spread",
 			PreemptionConfig: structs.PreemptionConfig{
 				SystemSchedulerEnabled:  true,
 				BatchSchedulerEnabled:   true,

command/agent/operator_endpoint.go

@@ -14,6 +14,8 @@ import (
 	"github.com/hashicorp/raft"
 )
 
+// OperatorRequest is used route operator/raft API requests to the implementing
+// functions.
 func (s *HTTPServer) OperatorRequest(resp http.ResponseWriter, req *http.Request) (interface{}, error) {
 	path := strings.TrimPrefix(req.URL.Path, "/v1/operator/raft/")
 	switch {
@@ -252,12 +254,17 @@ func (s *HTTPServer) schedulerUpdateConfig(resp http.ResponseWriter, req *http.R
 	}
 
 	args.Config = structs.SchedulerConfiguration{
+		SchedulerAlgorithm: structs.SchedulerAlgorithm(conf.SchedulerAlgorithm),
 		PreemptionConfig: structs.PreemptionConfig{
 			SystemSchedulerEnabled:  conf.PreemptionConfig.SystemSchedulerEnabled,
 			BatchSchedulerEnabled:   conf.PreemptionConfig.BatchSchedulerEnabled,
 			ServiceSchedulerEnabled: conf.PreemptionConfig.ServiceSchedulerEnabled},
 	}
 
+	if err := args.Config.Validate(); err != nil {
+		return nil, CodedError(http.StatusBadRequest, err.Error())
+	}
+
 	// Check for cas value
 	params := req.URL.Query()
 	if _, ok := params["cas"]; ok {

command/agent/testdata/basic.hcl

@@ -135,6 +135,8 @@ server {
   }
 
   default_scheduler_config {
+    scheduler_algorithm = "spread"
+
     preemption_config {
       batch_scheduler_enabled   = true
       system_scheduler_enabled  = true

command/agent/testdata/basic.json

@@ -297,6 +297,7 @@
         "2.2.2.2"
       ],
       "default_scheduler_config": [{
+        "scheduler_algorithm": "spread",
         "preemption_config": [{
           "batch_scheduler_enabled": true,
           "system_scheduler_enabled": true,

nomad/config.go

@@ -403,6 +403,7 @@ func DefaultConfig() *Config {
 		ServerHealthInterval: 2 * time.Second,
 		AutopilotInterval:    10 * time.Second,
 		DefaultSchedulerConfig: structs.SchedulerConfiguration{
+			SchedulerAlgorithm: structs.SchedulerAlgorithmBinpack,
 			PreemptionConfig: structs.PreemptionConfig{
 				SystemSchedulerEnabled:  true,
 				BatchSchedulerEnabled:   false,

nomad/structs/funcs.go

@@ -148,10 +148,7 @@ func AllocsFit(node *Node, allocs []*Allocation, netIdx *NetworkIndex, checkDevi
 	return true, "", used, nil
 }
 
-// ScoreFit is used to score the fit based on the Google work published here:
-// http://www.columbia.edu/~cs2035/courses/ieor4405.S13/datacenter_scheduling.ppt
-// This is equivalent to their BestFit v3
-func ScoreFit(node *Node, util *ComparableResources) float64 {
+func computeFreePercentage(node *Node, util *ComparableResources) (freePctCpu, freePctRam float64) {
 	// COMPAT(0.11): Remove in 0.11
 	reserved := node.ComparableReservedResources()
 	res := node.ComparableResources()
@@ -165,8 +162,18 @@ func ScoreFit(node *Node, util *ComparableResources) float64 {
 	}
 
 	// Compute the free percentage
-	freePctCpu := 1 - (float64(util.Flattened.Cpu.CpuShares) / nodeCpu)
-	freePctRam := 1 - (float64(util.Flattened.Memory.MemoryMB) / nodeMem)
+	freePctCpu = 1 - (float64(util.Flattened.Cpu.CpuShares) / nodeCpu)
+	freePctRam = 1 - (float64(util.Flattened.Memory.MemoryMB) / nodeMem)
+	return freePctCpu, freePctRam
+}
+
+// ScoreFitBinPack computes a fit score to achieve pinbacking behavior.
+// Score is in [0, 18]
+//
+// It's the BestFit v3 on the Google work published here:
+// http://www.columbia.edu/~cs2035/courses/ieor4405.S13/datacenter_scheduling.ppt
+func ScoreFitBinPack(node *Node, util *ComparableResources) float64 {
+	freePctCpu, freePctRam := computeFreePercentage(node, util)
 
 	// Total will be "maximized" the smaller the value is.
 	// At 100% utilization, the total is 2, while at 0% util it is 20.
@@ -187,6 +194,24 @@ func ScoreFit(node *Node, util *ComparableResources) float64 {
 	return score
 }
 
+// ScoreFitBinSpread computes a fit score to achieve spread behavior.
+// Score is in [0, 18]
+//
+// This is equivalent to Worst Fit of
+// http://www.columbia.edu/~cs2035/courses/ieor4405.S13/datacenter_scheduling.ppt
+func ScoreFitSpread(node *Node, util *ComparableResources) float64 {
+	freePctCpu, freePctRam := computeFreePercentage(node, util)
+	total := math.Pow(10, freePctCpu) + math.Pow(10, freePctRam)
+	score := total - 2
+
+	if score > 18.0 {
+		score = 18.0
+	} else if score < 0 {
+		score = 0
+	}
+	return score
+}
+
 func CopySliceConstraints(s []*Constraint) []*Constraint {
 	l := len(s)
 	if l == 0 {

nomad/structs/funcs_test.go

@@ -506,7 +506,7 @@ func TestAllocsFit_Devices(t *testing.T) {
 }
 
 // COMPAT(0.11): Remove in 0.11
-func TestScoreFit_Old(t *testing.T) {
+func TestScoreFitBinPack_Old(t *testing.T) {
 	node := &Node{}
 	node.Resources = &Resources{
 		CPU:      4096,
@@ -528,7 +528,7 @@ func TestScoreFit_Old(t *testing.T) {
 			},
 		},
 	}
-	score := ScoreFit(node, util)
+	score := ScoreFitBinPack(node, util)
 	if score != 18.0 {
 		t.Fatalf("bad: %v", score)
 	}
@@ -544,7 +544,7 @@ func TestScoreFit_Old(t *testing.T) {
 			},
 		},
 	}
-	score = ScoreFit(node, util)
+	score = ScoreFitBinPack(node, util)
 	if score != 0.0 {
 		t.Fatalf("bad: %v", score)
 	}
@@ -560,13 +560,13 @@ func TestScoreFit_Old(t *testing.T) {
 			},
 		},
 	}
-	score = ScoreFit(node, util)
+	score = ScoreFitBinPack(node, util)
 	if score < 10.0 || score > 16.0 {
 		t.Fatalf("bad: %v", score)
 	}
 }
 
-func TestScoreFit(t *testing.T) {
+func TestScoreFitBinPack(t *testing.T) {
 	node := &Node{}
 	node.NodeResources = &NodeResources{
 		Cpu: NodeCpuResources{
@@ -585,52 +585,53 @@ func TestScoreFit(t *testing.T) {
 		},
 	}
 
-	// Test a perfect fit
-	util := &ComparableResources{
-		Flattened: AllocatedTaskResources{
-			Cpu: AllocatedCpuResources{
-				CpuShares: 2048,
-			},
-			Memory: AllocatedMemoryResources{
-				MemoryMB: 4096,
+	cases := []struct {
+		name         string
+		flattened    AllocatedTaskResources
+		binPackScore float64
+		spreadScore  float64
+	}{
+		{
+			name: "almost filled node, but with just enough hole",
+			flattened: AllocatedTaskResources{
+				Cpu:    AllocatedCpuResources{CpuShares: 2048},
+				Memory: AllocatedMemoryResources{MemoryMB: 4096},
 			},
+			binPackScore: 18,
+			spreadScore:  0,
 		},
-	}
-	score := ScoreFit(node, util)
-	if score != 18.0 {
-		t.Fatalf("bad: %v", score)
-	}
-
-	// Test the worst fit
-	util = &ComparableResources{
-		Flattened: AllocatedTaskResources{
-			Cpu: AllocatedCpuResources{
-				CpuShares: 0,
-			},
-			Memory: AllocatedMemoryResources{
-				MemoryMB: 0,
+		{
+			name: "unutilized node",
+			flattened: AllocatedTaskResources{
+				Cpu:    AllocatedCpuResources{CpuShares: 0},
+				Memory: AllocatedMemoryResources{MemoryMB: 0},
 			},
+			binPackScore: 0,
+			spreadScore:  18,
 		},
-	}
-	score = ScoreFit(node, util)
-	if score != 0.0 {
-		t.Fatalf("bad: %v", score)
-	}
-
-	// Test a mid-case scenario
-	util = &ComparableResources{
-		Flattened: AllocatedTaskResources{
-			Cpu: AllocatedCpuResources{
-				CpuShares: 1024,
-			},
-			Memory: AllocatedMemoryResources{
-				MemoryMB: 2048,
+		{
+			name: "mid-case scnario",
+			flattened: AllocatedTaskResources{
+				Cpu:    AllocatedCpuResources{CpuShares: 1024},
+				Memory: AllocatedMemoryResources{MemoryMB: 2048},
 			},
+			binPackScore: 13.675,
+			spreadScore:  4.325,
 		},
 	}
-	score = ScoreFit(node, util)
-	if score < 10.0 || score > 16.0 {
-		t.Fatalf("bad: %v", score)
+
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			util := &ComparableResources{Flattened: c.flattened}
+
+			binPackScore := ScoreFitBinPack(node, util)
+			require.InDelta(t, c.binPackScore, binPackScore, 0.001, "binpack score")
+
+			spreadScore := ScoreFitSpread(node, util)
+			require.InDelta(t, c.spreadScore, spreadScore, 0.001, "spread score")
+
+			require.InDelta(t, 18, binPackScore+spreadScore, 0.001, "score sum")
+		})
 	}
 }
 

nomad/structs/operator.go

@@ -1,6 +1,7 @@
 package structs
 
 import (
+	"fmt"
 	"time"
 
 	"github.com/hashicorp/raft"
@@ -124,8 +125,26 @@ type AutopilotConfig struct {
 	ModifyIndex uint64
 }
 
+// SchedulerAlgorithm is an enum string that encapsulates the valid options for a
+// SchedulerConfiguration stanza's SchedulerAlgorithm. These modes will allow the
+// scheduler to be user-selectable.
+type SchedulerAlgorithm string
+
+const (
+	// SchedulerAlgorithmBinpack indicates that the scheduler should spread
+	// allocations as evenly as possible over the available hardware.
+	SchedulerAlgorithmBinpack SchedulerAlgorithm = "binpack"
+
+	// SchedulerAlgorithmSpread indicates that the scheduler should spread
+	// allocations as evenly as possible over the available hardware.
+	SchedulerAlgorithmSpread SchedulerAlgorithm = "spread"
+)
+
 // SchedulerConfiguration is the config for controlling scheduler behavior
 type SchedulerConfiguration struct {
+	// SchedulerAlgorithm lets you select between available scheduling algorithms.
+	SchedulerAlgorithm SchedulerAlgorithm `hcl:"scheduler_algorithm"`
+
 	// PreemptionConfig specifies whether to enable eviction of lower
 	// priority jobs to place higher priority jobs.
 	PreemptionConfig PreemptionConfig `hcl:"preemption_config"`
@@ -135,6 +154,28 @@ type SchedulerConfiguration struct {
 	ModifyIndex uint64
 }
 
+func (s *SchedulerConfiguration) EffectiveSchedulerAlgorithm() SchedulerAlgorithm {
+	if s == nil || s.SchedulerAlgorithm == "" {
+		return SchedulerAlgorithmBinpack
+	}
+
+	return s.SchedulerAlgorithm
+}
+
+func (s *SchedulerConfiguration) Validate() error {
+	if s == nil {
+		return nil
+	}
+
+	switch s.SchedulerAlgorithm {
+	case "", SchedulerAlgorithmBinpack, SchedulerAlgorithmSpread:
+	default:
+		return fmt.Errorf("invalid scheduler algorithm: %v", s.SchedulerAlgorithm)
+	}
+
+	return nil
+}
+
 // SchedulerConfigurationResponse is the response object that wraps SchedulerConfiguration
 type SchedulerConfigurationResponse struct {
 	// SchedulerConfig contains scheduler config options

scheduler/preemption_test.go

@@ -1349,7 +1349,7 @@ func TestPreemption(t *testing.T) {
 				ctx.plan.NodePreemptions[node.ID] = tc.currentPreemptions
 			}
 			static := NewStaticRankIterator(ctx, nodes)
-			binPackIter := NewBinPackIterator(ctx, static, true, tc.jobPriority)
+			binPackIter := NewBinPackIterator(ctx, static, true, tc.jobPriority, structs.SchedulerAlgorithmBinpack)
 			job := mock.Job()
 			job.Priority = tc.jobPriority
 			binPackIter.SetJob(job)