Topology-aware scheduling

This adds support for placement preferences in Swarm services.

- Convert PlacementPreferences between GRPC API and HTTP API
- Add --placement-pref, --placement-pref-add and --placement-pref-rm to CLI
- Add support for placement preferences in service inspect --pretty
- Add integration test

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

command/formatter/service.go

@@ -39,9 +39,12 @@ UpdateStatus:
  Message:	{{ .UpdateStatusMessage }}
 {{- end }}
 Placement:
-{{- if .TaskPlacementConstraints -}}
+{{- if .TaskPlacementConstraints }}
  Constraints:	{{ .TaskPlacementConstraints }}
 {{- end }}
+{{- if .TaskPlacementPreferences }}
+ Preferences:   {{ .TaskPlacementPreferences }}
+{{- end }}
 {{- if .HasUpdateConfig }}
 UpdateConfig:
  Parallelism:	{{ .UpdateParallelism }}
@@ -211,6 +214,19 @@ func (ctx *serviceInspectContext) TaskPlacementConstraints() []string {
 	return nil
 }
 
+func (ctx *serviceInspectContext) TaskPlacementPreferences() []string {
+	if ctx.Service.Spec.TaskTemplate.Placement == nil {
+		return nil
+	}
+	var strings []string
+	for _, pref := range ctx.Service.Spec.TaskTemplate.Placement.Preferences {
+		if pref.Spread != nil {
+			strings = append(strings, "spread="+pref.Spread.SpreadDescriptor)
+		}
+	}
+	return strings
+}
+
 func (ctx *serviceInspectContext) HasUpdateConfig() bool {
 	return ctx.Service.Spec.UpdateConfig != nil
 }

command/service/create.go

@@ -37,6 +37,8 @@ func newCreateCommand(dockerCli *command.DockerCli) *cobra.Command {
 	flags.Var(&opts.envFile, flagEnvFile, "Read in a file of environment variables")
 	flags.Var(&opts.mounts, flagMount, "Attach a filesystem mount to the service")
 	flags.Var(&opts.constraints, flagConstraint, "Placement constraints")
+	flags.Var(&opts.placementPrefs, flagPlacementPref, "Add a placement preference")
+	flags.SetAnnotation(flagPlacementPref, "version", []string{"1.27"})
 	flags.Var(&opts.networks, flagNetwork, "Network attachments")
 	flags.Var(&opts.secrets, flagSecret, "Specify secrets to expose to the service")
 	flags.SetAnnotation(flagSecret, "version", []string{"1.25"})

command/service/opts.go

@@ -1,6 +1,7 @@
 package service
 
 import (
+	"errors"
 	"fmt"
 	"strconv"
 	"strings"
@@ -117,6 +118,45 @@ func (f *floatValue) Value() float32 {
 	return float32(*f)
 }
 
+// placementPrefOpts holds a list of placement preferences.
+type placementPrefOpts struct {
+	prefs   []swarm.PlacementPreference
+	strings []string
+}
+
+func (opts *placementPrefOpts) String() string {
+	if len(opts.strings) == 0 {
+		return ""
+	}
+	return fmt.Sprintf("%v", opts.strings)
+}
+
+// Set validates the input value and adds it to the internal slices.
+// Note: in the future strategies other than "spread", may be supported,
+// as well as additional comma-separated options.
+func (opts *placementPrefOpts) Set(value string) error {
+	fields := strings.Split(value, "=")
+	if len(fields) != 2 {
+		return errors.New(`placement preference must be of the format "<strategy>=<arg>"`)
+	}
+	if fields[0] != "spread" {
+		return fmt.Errorf("unsupported placement preference %s (only spread is supported)", fields[0])
+	}
+
+	opts.prefs = append(opts.prefs, swarm.PlacementPreference{
+		Spread: &swarm.SpreadOver{
+			SpreadDescriptor: fields[1],
+		},
+	})
+	opts.strings = append(opts.strings, value)
+	return nil
+}
+
+// Type returns a string name for this Option type
+func (opts *placementPrefOpts) Type() string {
+	return "pref"
+}
+
 type updateOptions struct {
 	parallelism     uint64
 	delay           time.Duration
@@ -285,6 +325,7 @@ type serviceOptions struct {
 
 	restartPolicy  restartPolicyOptions
 	constraints    opts.ListOpts
+	placementPrefs placementPrefOpts
 	update         updateOptions
 	networks       opts.ListOpts
 	endpoint       endpointOptions
@@ -398,6 +439,7 @@ func (opts *serviceOptions) ToService() (swarm.ServiceSpec, error) {
 			RestartPolicy: opts.restartPolicy.ToRestartPolicy(),
 			Placement: &swarm.Placement{
 				Constraints: opts.constraints.GetAll(),
+				Preferences: opts.placementPrefs.prefs,
 			},
 			LogDriver: opts.logDriver.toLogDriver(),
 		},
@@ -473,6 +515,9 @@ func addServiceFlags(cmd *cobra.Command, opts *serviceOptions) {
 }
 
 const (
+	flagPlacementPref         = "placement-pref"
+	flagPlacementPrefAdd      = "placement-pref-add"
+	flagPlacementPrefRemove   = "placement-pref-rm"
 	flagConstraint            = "constraint"
 	flagConstraintRemove      = "constraint-rm"
 	flagConstraintAdd         = "constraint-add"

command/service/update.go

@@ -69,6 +69,10 @@ func newUpdateCommand(dockerCli *command.DockerCli) *cobra.Command {
 	flags.SetAnnotation(flagSecretAdd, "version", []string{"1.25"})
 	flags.Var(&serviceOpts.mounts, flagMountAdd, "Add or update a mount on a service")
 	flags.Var(&serviceOpts.constraints, flagConstraintAdd, "Add or update a placement constraint")
+	flags.Var(&serviceOpts.placementPrefs, flagPlacementPrefAdd, "Add a placement preference")
+	flags.SetAnnotation(flagPlacementPrefAdd, "version", []string{"1.27"})
+	flags.Var(&placementPrefOpts{}, flagPlacementPrefRemove, "Remove a placement preference")
+	flags.SetAnnotation(flagPlacementPrefRemove, "version", []string{"1.27"})
 	flags.Var(&serviceOpts.endpoint.publishPorts, flagPublishAdd, "Add or update a published port")
 	flags.Var(&serviceOpts.groups, flagGroupAdd, "Add an additional supplementary user group to the container")
 	flags.SetAnnotation(flagGroupAdd, "version", []string{"1.25"})
@@ -260,7 +264,14 @@ func updateService(flags *pflag.FlagSet, spec *swarm.ServiceSpec) error {
 		if task.Placement == nil {
 			task.Placement = &swarm.Placement{}
 		}
-		updatePlacement(flags, task.Placement)
+		updatePlacementConstraints(flags, task.Placement)
+	}
+
+	if anyChanged(flags, flagPlacementPrefAdd, flagPlacementPrefRemove) {
+		if task.Placement == nil {
+			task.Placement = &swarm.Placement{}
+		}
+		updatePlacementPreferences(flags, task.Placement)
 	}
 
 	if err := updateReplicas(flags, &spec.Mode); err != nil {
@@ -372,7 +383,7 @@ func anyChanged(flags *pflag.FlagSet, fields ...string) bool {
 	return false
 }
 
-func updatePlacement(flags *pflag.FlagSet, placement *swarm.Placement) {
+func updatePlacementConstraints(flags *pflag.FlagSet, placement *swarm.Placement) {
 	if flags.Changed(flagConstraintAdd) {
 		values := flags.Lookup(flagConstraintAdd).Value.(*opts.ListOpts).GetAll()
 		placement.Constraints = append(placement.Constraints, values...)
@@ -391,6 +402,35 @@ func updatePlacement(flags *pflag.FlagSet, placement *swarm.Placement) {
 	placement.Constraints = newConstraints
 }
 
+func updatePlacementPreferences(flags *pflag.FlagSet, placement *swarm.Placement) {
+	var newPrefs []swarm.PlacementPreference
+
+	if flags.Changed(flagPlacementPrefRemove) {
+		for _, existing := range placement.Preferences {
+			removed := false
+			for _, removal := range flags.Lookup(flagPlacementPrefRemove).Value.(*placementPrefOpts).prefs {
+				if removal.Spread != nil && existing.Spread != nil && removal.Spread.SpreadDescriptor == existing.Spread.SpreadDescriptor {
+					removed = true
+					break
+				}
+			}
+			if !removed {
+				newPrefs = append(newPrefs, existing)
+			}
+		}
+	} else {
+		newPrefs = placement.Preferences
+	}
+
+	if flags.Changed(flagPlacementPrefAdd) {
+		for _, addition := range flags.Lookup(flagPlacementPrefAdd).Value.(*placementPrefOpts).prefs {
+			newPrefs = append(newPrefs, addition)
+		}
+	}
+
+	placement.Preferences = newPrefs
+}
+
 func updateContainerLabels(flags *pflag.FlagSet, field *map[string]string) {
 	if flags.Changed(flagContainerLabelAdd) {
 		if *field == nil {

command/service/update_test.go

@@ -51,7 +51,7 @@ func TestUpdateLabelsRemoveALabelThatDoesNotExist(t *testing.T) {
 	assert.Equal(t, len(labels), 1)
 }
 
-func TestUpdatePlacement(t *testing.T) {
+func TestUpdatePlacementConstraints(t *testing.T) {
 	flags := newUpdateCommand(nil).Flags()
 	flags.Set("constraint-add", "node=toadd")
 	flags.Set("constraint-rm", "node!=toremove")
@@ -60,12 +60,38 @@ func TestUpdatePlacement(t *testing.T) {
 		Constraints: []string{"node!=toremove", "container=tokeep"},
 	}
 
-	updatePlacement(flags, placement)
+	updatePlacementConstraints(flags, placement)
 	assert.Equal(t, len(placement.Constraints), 2)
 	assert.Equal(t, placement.Constraints[0], "container=tokeep")
 	assert.Equal(t, placement.Constraints[1], "node=toadd")
 }
 
+func TestUpdatePlacementPrefs(t *testing.T) {
+	flags := newUpdateCommand(nil).Flags()
+	flags.Set("placement-pref-add", "spread=node.labels.dc")
+	flags.Set("placement-pref-rm", "spread=node.labels.rack")
+
+	placement := &swarm.Placement{
+		Preferences: []swarm.PlacementPreference{
+			{
+				Spread: &swarm.SpreadOver{
+					SpreadDescriptor: "node.labels.rack",
+				},
+			},
+			{
+				Spread: &swarm.SpreadOver{
+					SpreadDescriptor: "node.labels.row",
+				},
+			},
+		},
+	}
+
+	updatePlacementPreferences(flags, placement)
+	assert.Equal(t, len(placement.Preferences), 2)
+	assert.Equal(t, placement.Preferences[0].Spread.SpreadDescriptor, "node.labels.row")
+	assert.Equal(t, placement.Preferences[1].Spread.SpreadDescriptor, "node.labels.dc")
+}
+
 func TestUpdateEnvironment(t *testing.T) {
 	flags := newUpdateCommand(nil).Flags()
 	flags.Set("env-add", "toadd=newenv")