Allow non valid zones for instances to be add to a placement (#1479)

* Allow non valid zones for instances to be add to a placement

* Address feedback

* - rename test
  - generate mock

* Address feedback

src/cluster/placement/options.go

@@ -33,6 +33,9 @@ const (
 	defaultIsSharded   = true
 	// By default partial replace should be allowed for better distribution.
 	defaultAllowPartialReplace = true
+	// By default the zone of the hosts within a placement should match the zone
+	// that the placement was created with.
+	defaultAllowAllZones = false
 )
 
 type deploymentOptions struct {
@@ -68,6 +71,7 @@ type options struct {
 	validateFn          ValidateFn
 	nowFn               clock.NowFn
 	allowPartialReplace bool
+	allowAllZones       bool
 	addAllCandidates    bool
 	dryrun              bool
 	isSharded           bool
@@ -89,6 +93,7 @@ func NewOptions() Options {
 		isShardCutoffFn:     defaultShardValidationFn,
 		validateFn:          Validate,
 		nowFn:               time.Now,
+		allowAllZones:       defaultAllowAllZones,
 	}
 }
 
@@ -101,6 +106,15 @@ func (o options) SetAllowPartialReplace(allowPartialReplace bool) Options {
 	return o
 }
 
+func (o options) AllowAllZones() bool {
+	return o.allowAllZones
+}
+
+func (o options) SetAllowAllZones(allowAllZones bool) Options {
+	o.allowAllZones = allowAllZones
+	return o
+}
+
 func (o options) AddAllCandidates() bool {
 	return o.addAllCandidates
 }

src/cluster/placement/selector/common.go

@@ -69,6 +69,9 @@ func filterZones(
 	var validZone string
 	if opts != nil {
 		validZone = opts.ValidZone()
+		if opts.AllowAllZones() {
+			return candidates
+		}
 	}
 	if validZone == "" && len(p.Instances()) > 0 {
 		validZone = p.Instances()[0].Zone()

src/cluster/placement/selector/common_test.go

@@ -52,3 +52,22 @@ func TestGetValidCandidates(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, []placement.Instance{i3, i3, i4}, res)
 }
+
+func TestGetValidCandidatesAllowAllZones(t *testing.T) {
+	i1 := placement.NewInstance().SetID("i1").SetZone("z1")
+	i2 := placement.NewInstance().SetID("i2").SetZone("z1")
+	i3 := placement.NewInstance().SetID("i3").SetZone("z2")
+
+	p := placement.NewPlacement().
+		SetInstances([]placement.Instance{i3, i1, i2}).
+		SetIsSharded(false).
+		SetReplicaFactor(1)
+
+	i4 := placement.NewInstance().SetID("i4").SetZone("z2")
+	i5 := placement.NewInstance().SetID("i5").SetZone("z3")
+	candidates := []placement.Instance{i4, i5}
+	res, err := getValidCandidates(p, candidates, placement.NewOptions().
+		SetAllowAllZones(true))
+	require.NoError(t, err)
+	require.Equal(t, []placement.Instance{i4, i5}, res)
+}

src/cluster/placement/types.go

@@ -336,6 +336,14 @@ type Options interface {
 	// SetAllowPartialReplace sets AllowPartialReplace.
 	SetAllowPartialReplace(allowPartialReplace bool) Options
 
+	// AllowAllZones will enable the placement to contain hosts that
+	// are not contained within the same zone of the actual placement. This is
+	// needed for services that require cross zone communication.
+	AllowAllZones() bool
+
+	// SetAllowAllZones sets AllowAllZones.
+	SetAllowAllZones(allowAllZones bool) Options
+
 	// AddAllCandidates determines whether the placement will attempt to add all
 	// candidates when adding instances or just a single one.
 	AddAllCandidates() bool