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Distinct Property supports arbitrary limit 

This PR enhances the distinct_property constraint such that a limit can
be specified in the RTarget/value parameter. This allows constraints
such as:

```
constraint {
  distinct_property = "${meta.rack}"
  value = "2"
}
```

This restricts any given rack from running more than 2 allocations from
the task group.

Fixes https://github.com/hashicorp/nomad/issues/1146
This commit is contained in:
Alex Dadgar 2017-07-31 16:44:17 -07:00
parent 5a750a3735
commit 2650bb1d12
8 changed files with 506 additions and 66 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
helper/funcs.go
View File

@ -76,6 +76,20 @@ func IntMin(a, b int) int {
return b
}
func IntMax(a, b int) int {
if a > b {
return a
}
return b
}
func Uint64Max(a, b uint64) uint64 {
if a > b {
return a
}
return b
}
// MapStringStringSliceValueSet returns the set of values in a map[string][]string
func MapStringStringSliceValueSet(m map[string][]string) []string {
set := make(map[string]struct{})

38
nomad/structs/structs.go
View File

@ -3874,8 +3874,24 @@ func (c *Constraint) Validate() error {
mErr.Errors = append(mErr.Errors, errors.New("Missing constraint operand"))
}
// requireLtarget specifies whether the constraint requires an LTarget to be
// provided.
requireLtarget := true
// Perform additional validation based on operand
switch c.Operand {
case ConstraintDistinctHosts:
requireLtarget = false
if c.RTarget != "" {
mErr.Errors = append(mErr.Errors, fmt.Errorf("Distinct hosts constraint doesn't allow RTarget. Got %q", c.RTarget))
}
if c.LTarget != "" {
mErr.Errors = append(mErr.Errors, fmt.Errorf("Distinct hosts constraint doesn't allow LTarget. Got %q", c.LTarget))
}
case ConstraintSetContains:
if c.RTarget == "" {
mErr.Errors = append(mErr.Errors, fmt.Errorf("Set contains constraint requires an RTarget"))
}
case ConstraintRegex:
if _, err := regexp.Compile(c.RTarget); err != nil {
mErr.Errors = append(mErr.Errors, fmt.Errorf("Regular expression failed to compile: %v", err))
@ -3884,7 +3900,29 @@ func (c *Constraint) Validate() error {
if _, err := version.NewConstraint(c.RTarget); err != nil {
mErr.Errors = append(mErr.Errors, fmt.Errorf("Version constraint is invalid: %v", err))
}
case ConstraintDistinctProperty:
// If a count is set, make sure it is convertible to a uint64
if c.RTarget != "" {
count, err := strconv.ParseUint(c.RTarget, 10, 64)
if err != nil {
mErr.Errors = append(mErr.Errors, fmt.Errorf("Failed to convert RTarget %q to uint64: %v", c.RTarget, err))
} else if count < 1 {
mErr.Errors = append(mErr.Errors, fmt.Errorf("Distinct Property must have an allowed count of 1 or greater: %d < 1", count))
}
}
case "=", "==", "is", "!=", "not", "<", "<=", ">", ">=":
if c.RTarget == "" {
mErr.Errors = append(mErr.Errors, fmt.Errorf("Operator %q requires an RTarget", c.Operand))
}
default:
mErr.Errors = append(mErr.Errors, fmt.Errorf("Unknown constraint type %q", c.Operand))
}
// Ensure we have an LTarget for the constraints that need one
if requireLtarget && c.LTarget == "" {
mErr.Errors = append(mErr.Errors, fmt.Errorf("No LTarget provided but is required by constraint"))
}
return mErr.ErrorOrNil()
}

55
nomad/structs/structs_test.go
View File

@ -1323,6 +1323,61 @@ func TestConstraint_Validate(t *testing.T) {
if !strings.Contains(mErr.Errors[0].Error(), "Malformed constraint") {
t.Fatalf("err: %s", err)
}
// Perform distinct_property validation
c.Operand = ConstraintDistinctProperty
c.RTarget = "0"
err = c.Validate()
mErr = err.(*multierror.Error)
if !strings.Contains(mErr.Errors[0].Error(), "count of 1 or greater") {
t.Fatalf("err: %s", err)
}
c.RTarget = "-1"
err = c.Validate()
mErr = err.(*multierror.Error)
if !strings.Contains(mErr.Errors[0].Error(), "to uint64") {
t.Fatalf("err: %s", err)
}
// Perform distinct_hosts validation
c.Operand = ConstraintDistinctHosts
c.RTarget = "foo"
err = c.Validate()
mErr = err.(*multierror.Error)
if !strings.Contains(mErr.Errors[0].Error(), "doesn't allow RTarget") {
t.Fatalf("err: %s", err)
}
if !strings.Contains(mErr.Errors[1].Error(), "doesn't allow LTarget") {
t.Fatalf("err: %s", err)
}
// Perform set_contains validation
c.Operand = ConstraintSetContains
c.RTarget = ""
err = c.Validate()
mErr = err.(*multierror.Error)
if !strings.Contains(mErr.Errors[0].Error(), "requires an RTarget") {
t.Fatalf("err: %s", err)
}
// Perform LTarget validation
c.Operand = ConstraintRegex
c.RTarget = "foo"
c.LTarget = ""
err = c.Validate()
mErr = err.(*multierror.Error)
if !strings.Contains(mErr.Errors[0].Error(), "No LTarget") {
t.Fatalf("err: %s", err)
}
// Perform constraint type validation
c.Operand = "foo"
err = c.Validate()
mErr = err.(*multierror.Error)
if !strings.Contains(mErr.Errors[0].Error(), "Unknown constraint type") {
t.Fatalf("err: %s", err)
}
}
func TestUpdateStrategy_Validate(t *testing.T) {

282
scheduler/feasible_test.go
View File

@ -782,6 +782,198 @@ func TestDistinctPropertyIterator_JobDistinctProperty(t *testing.T) {
}
}
// This test creates allocations across task groups that use a property value to
// detect if the constraint at the job level properly considers all task groups
// when the constraint allows a count greater than one
func TestDistinctPropertyIterator_JobDistinctProperty_Count(t *testing.T) {
state, ctx := testContext(t)
nodes := []*structs.Node{
mock.Node(),
mock.Node(),
mock.Node(),
}
for i, n := range nodes {
n.Meta["rack"] = fmt.Sprintf("%d", i)
// Add to state store
if err := state.UpsertNode(uint64(100+i), n); err != nil {
t.Fatalf("failed to upsert node: %v", err)
}
}
static := NewStaticIterator(ctx, nodes)
// Create a job with a distinct_property constraint and a task groups.
tg1 := &structs.TaskGroup{Name: "bar"}
tg2 := &structs.TaskGroup{Name: "baz"}
job := &structs.Job{
ID: "foo",
Constraints: []*structs.Constraint{
{
Operand: structs.ConstraintDistinctProperty,
LTarget: "${meta.rack}",
RTarget: "2",
},
},
TaskGroups: []*structs.TaskGroup{tg1, tg2},
}
// Add allocs placing two allocations on both node 1 and 2 and only one on
// node 3. This should make the job unsatisfiable on all nodes but node5.
// Also mix the allocations existing in the plan and the state store.
plan := ctx.Plan()
alloc1ID := structs.GenerateUUID()
plan.NodeAllocation[nodes[0].ID] = []*structs.Allocation{
&structs.Allocation{
TaskGroup: tg1.Name,
JobID: job.ID,
Job: job,
ID: alloc1ID,
NodeID: nodes[0].ID,
},
&structs.Allocation{
TaskGroup: tg2.Name,
JobID: job.ID,
Job: job,
ID: alloc1ID,
NodeID: nodes[0].ID,
},
// Should be ignored as it is a different job.
&structs.Allocation{
TaskGroup: tg2.Name,
JobID: "ignore 2",
Job: job,
ID: structs.GenerateUUID(),
NodeID: nodes[0].ID,
},
}
plan.NodeAllocation[nodes[1].ID] = []*structs.Allocation{
&structs.Allocation{
TaskGroup: tg1.Name,
JobID: job.ID,
Job: job,
ID: structs.GenerateUUID(),
NodeID: nodes[1].ID,
},
&structs.Allocation{
TaskGroup: tg2.Name,
JobID: job.ID,
Job: job,
ID: structs.GenerateUUID(),
NodeID: nodes[1].ID,
},
// Should be ignored as it is a different job.
&structs.Allocation{
TaskGroup: tg1.Name,
JobID: "ignore 2",
Job: job,
ID: structs.GenerateUUID(),
NodeID: nodes[1].ID,
},
}
plan.NodeAllocation[nodes[2].ID] = []*structs.Allocation{
&structs.Allocation{
TaskGroup: tg1.Name,
JobID: job.ID,
Job: job,
ID: structs.GenerateUUID(),
NodeID: nodes[2].ID,
},
// Should be ignored as it is a different job.
&structs.Allocation{
TaskGroup: tg1.Name,
JobID: "ignore 2",
Job: job,
ID: structs.GenerateUUID(),
NodeID: nodes[2].ID,
},
}
// Put an allocation on Node 3 but make it stopped in the plan
stoppingAllocID := structs.GenerateUUID()
plan.NodeUpdate[nodes[2].ID] = []*structs.Allocation{
&structs.Allocation{
TaskGroup: tg2.Name,
JobID: job.ID,
Job: job,
ID: stoppingAllocID,
NodeID: nodes[2].ID,
},
}
upserting := []*structs.Allocation{
// Have one of the allocations exist in both the plan and the state
// store. This resembles an allocation update
&structs.Allocation{
TaskGroup: tg1.Name,
JobID: job.ID,
Job: job,
ID: alloc1ID,
EvalID: structs.GenerateUUID(),
NodeID: nodes[0].ID,
},
&structs.Allocation{
TaskGroup: tg1.Name,
JobID: job.ID,
Job: job,
ID: structs.GenerateUUID(),
EvalID: structs.GenerateUUID(),
NodeID: nodes[1].ID,
},
&structs.Allocation{
TaskGroup: tg2.Name,
JobID: job.ID,
Job: job,
ID: structs.GenerateUUID(),
EvalID: structs.GenerateUUID(),
NodeID: nodes[0].ID,
},
// Should be ignored as it is a different job.
&structs.Allocation{
TaskGroup: tg1.Name,
JobID: "ignore 2",
Job: job,
ID: structs.GenerateUUID(),
EvalID: structs.GenerateUUID(),
NodeID: nodes[1].ID,
},
&structs.Allocation{
TaskGroup: tg2.Name,
JobID: "ignore 2",
Job: job,
ID: structs.GenerateUUID(),
EvalID: structs.GenerateUUID(),
NodeID: nodes[1].ID,
},
}
if err := state.UpsertAllocs(1000, upserting); err != nil {
t.Fatalf("failed to UpsertAllocs: %v", err)
}
proposed := NewDistinctPropertyIterator(ctx, static)
proposed.SetJob(job)
proposed.SetTaskGroup(tg2)
proposed.Reset()
out := collectFeasible(proposed)
if len(out) != 1 {
t.Fatalf("Bad: %#v", out)
}
if out[0].ID != nodes[2].ID {
t.Fatalf("wrong node picked")
}
}
// This test checks that if a node has an allocation on it that gets stopped,
// there is a plan to re-use that for a new allocation, that the next select
// won't select that node.
@ -934,6 +1126,96 @@ func TestDistinctPropertyIterator_JobDistinctProperty_Infeasible(t *testing.T) {
}
}
// This test creates previous allocations selecting certain property values to
// test if it detects infeasibility of property values correctly and picks the
// only feasible one
func TestDistinctPropertyIterator_JobDistinctProperty_Infeasible_Count(t *testing.T) {
state, ctx := testContext(t)
nodes := []*structs.Node{
mock.Node(),
mock.Node(),
}
for i, n := range nodes {
n.Meta["rack"] = fmt.Sprintf("%d", i)
// Add to state store
if err := state.UpsertNode(uint64(100+i), n); err != nil {
t.Fatalf("failed to upsert node: %v", err)
}
}
static := NewStaticIterator(ctx, nodes)
// Create a job with a distinct_property constraint and a task groups.
tg1 := &structs.TaskGroup{Name: "bar"}
tg2 := &structs.TaskGroup{Name: "baz"}
tg3 := &structs.TaskGroup{Name: "bam"}
job := &structs.Job{
ID: "foo",
Constraints: []*structs.Constraint{
{
Operand: structs.ConstraintDistinctProperty,
LTarget: "${meta.rack}",
RTarget: "2",
},
},
TaskGroups: []*structs.TaskGroup{tg1, tg2, tg3},
}
// Add allocs placing two tg1's on node1 and two tg2's on node2. This should
// make the job unsatisfiable for tg3.
plan := ctx.Plan()
plan.NodeAllocation[nodes[0].ID] = []*structs.Allocation{
&structs.Allocation{
TaskGroup: tg1.Name,
JobID: job.ID,
Job: job,
ID: structs.GenerateUUID(),
NodeID: nodes[0].ID,
},
&structs.Allocation{
TaskGroup: tg2.Name,
JobID: job.ID,
Job: job,
ID: structs.GenerateUUID(),
NodeID: nodes[0].ID,
},
}
upserting := []*structs.Allocation{
&structs.Allocation{
TaskGroup: tg1.Name,
JobID: job.ID,
Job: job,
ID: structs.GenerateUUID(),
EvalID: structs.GenerateUUID(),
NodeID: nodes[1].ID,
},
&structs.Allocation{
TaskGroup: tg2.Name,
JobID: job.ID,
Job: job,
ID: structs.GenerateUUID(),
EvalID: structs.GenerateUUID(),
NodeID: nodes[1].ID,
},
}
if err := state.UpsertAllocs(1000, upserting); err != nil {
t.Fatalf("failed to UpsertAllocs: %v", err)
}
proposed := NewDistinctPropertyIterator(ctx, static)
proposed.SetJob(job)
proposed.SetTaskGroup(tg3)
proposed.Reset()
out := collectFeasible(proposed)
if len(out) != 0 {
t.Fatalf("Bad: %#v", out)
}
}
// This test creates previous allocations selecting certain property values to
// test if it detects infeasibility of property values correctly and picks the
// only feasible one when the constraint is at the task group.

26
scheduler/generic_sched_test.go
View File

@ -342,11 +342,12 @@ func TestServiceSched_JobRegister_DistinctProperty(t *testing.T) {
// Create a job that uses distinct property and has count higher than what is
// possible.
job := mock.Job()
job.TaskGroups[0].Count = 4
job.TaskGroups[0].Count = 8
job.Constraints = append(job.Constraints,
&structs.Constraint{
Operand: structs.ConstraintDistinctProperty,
LTarget: "${meta.rack}",
RTarget: "2",
})
noErr(t, h.State.UpsertJob(h.NextIndex(), job))
@ -391,7 +392,7 @@ func TestServiceSched_JobRegister_DistinctProperty(t *testing.T) {
for _, allocList := range plan.NodeAllocation {
planned = append(planned, allocList...)
}
if len(planned) != 2 {
if len(planned) != 4 {
t.Fatalf("bad: %#v", plan)
}
@ -401,17 +402,17 @@ func TestServiceSched_JobRegister_DistinctProperty(t *testing.T) {
noErr(t, err)
// Ensure all allocations placed
if len(out) != 2 {
if len(out) != 4 {
t.Fatalf("bad: %#v", out)
}
// Ensure different node was used per.
used := make(map[string]struct{})
// Ensure each node was only used twice
used := make(map[string]uint64)
for _, alloc := range out {
if _, ok := used[alloc.NodeID]; ok {
t.Fatalf("Node collision %v", alloc.NodeID)
if count, _ := used[alloc.NodeID]; count > 2 {
t.Fatalf("Node %v used too much: %d", alloc.NodeID, count)
}
used[alloc.NodeID] = struct{}{}
used[alloc.NodeID]++
}
h.AssertEvalStatus(t, structs.EvalStatusComplete)
@ -427,8 +428,7 @@ func TestServiceSched_JobRegister_DistinctProperty_TaskGroup(t *testing.T) {
noErr(t, h.State.UpsertNode(h.NextIndex(), node))
}
// Create a job that uses distinct property and has count higher than what is
// possible.
// Create a job that uses distinct property only on one task group.
job := mock.Job()
job.TaskGroups = append(job.TaskGroups, job.TaskGroups[0].Copy())
job.TaskGroups[0].Count = 1
@ -439,7 +439,7 @@ func TestServiceSched_JobRegister_DistinctProperty_TaskGroup(t *testing.T) {
})
job.TaskGroups[1].Name = "tg2"
job.TaskGroups[1].Count = 1
job.TaskGroups[1].Count = 2
noErr(t, h.State.UpsertJob(h.NextIndex(), job))
// Create a mock evaluation to register the job
@ -477,7 +477,7 @@ func TestServiceSched_JobRegister_DistinctProperty_TaskGroup(t *testing.T) {
for _, allocList := range plan.NodeAllocation {
planned = append(planned, allocList...)
}
if len(planned) != 2 {
if len(planned) != 3 {
t.Fatalf("bad: %#v", plan)
}
@ -487,7 +487,7 @@ func TestServiceSched_JobRegister_DistinctProperty_TaskGroup(t *testing.T) {
noErr(t, err)
// Ensure all allocations placed
if len(out) != 2 {
if len(out) != 3 {
t.Fatalf("bad: %#v", out)
}

129
scheduler/propertyset.go
View File

@ -2,8 +2,10 @@ package scheduler
import (
"fmt"
"strconv"
memdb "github.com/hashicorp/go-memdb"
"github.com/hashicorp/nomad/helper"
"github.com/hashicorp/nomad/nomad/structs"
)
@ -21,21 +23,25 @@ type propertySet struct {
// constraint is the constraint this property set is checking
constraint *structs.Constraint
// allowedCount is the allowed number of allocations that can have the
// distinct property
allowedCount uint64
// errorBuilding marks whether there was an error when building the property
// set
errorBuilding error
// existingValues is the set of values for the given property that have been
// used by pre-existing allocations.
existingValues map[string]struct{}
// existingValues is a mapping of the values of a property to the number of
// times the value has been used by pre-existing allocations.
existingValues map[string]uint64
// proposedValues is the set of values for the given property that are used
// from proposed allocations.
proposedValues map[string]struct{}
// proposedValues is a mapping of the values of a property to the number of
// times the value has been used by proposed allocations.
proposedValues map[string]uint64
// clearedValues is the set of values that are no longer being used by
// existingValues because of proposed stops.
clearedValues map[string]struct{}
// clearedValues is a mapping of the values of a property to the number of
// times the value has been used by proposed stopped allocations.
clearedValues map[string]uint64
}
// NewPropertySet returns a new property set used to guarantee unique property
@ -44,7 +50,7 @@ func NewPropertySet(ctx Context, job *structs.Job) *propertySet {
p := &propertySet{
ctx: ctx,
jobID: job.ID,
existingValues: make(map[string]struct{}),
existingValues: make(map[string]uint64),
}
return p
@ -53,26 +59,42 @@ func NewPropertySet(ctx Context, job *structs.Job) *propertySet {
// SetJobConstraint is used to parameterize the property set for a
// distinct_property constraint set at the job level.
func (p *propertySet) SetJobConstraint(constraint *structs.Constraint) {
// Store the constraint
p.constraint = constraint
p.populateExisting(constraint)
// Populate the proposed when setting the constraint. We do this because
// when detecting if we can inplace update an allocation we stage an
// eviction and then select. This means the plan has an eviction before a
// single select has finished.
p.PopulateProposed()
p.setConstraint(constraint, "")
}
// SetTGConstraint is used to parameterize the property set for a
// distinct_property constraint set at the task group level. The inputs are the
// constraint and the task group name.
func (p *propertySet) SetTGConstraint(constraint *structs.Constraint, taskGroup string) {
p.setConstraint(constraint, taskGroup)
}
// setConstraint is a shared helper for setting a job or task group constraint.
func (p *propertySet) setConstraint(constraint *structs.Constraint, taskGroup string) {
// Store that this is for a task group
p.taskGroup = taskGroup
if taskGroup != "" {
p.taskGroup = taskGroup
}
// Store the constraint
p.constraint = constraint
// Determine the number of allowed allocations with the property.
if v := constraint.RTarget; v != "" {
c, err := strconv.ParseUint(v, 10, 64)
if err != nil {
p.errorBuilding = fmt.Errorf("failed to convert RTarget %q to uint64: %v", v, err)
p.ctx.Logger().Printf("[ERR] scheduler.dynamic-constraint: %v", p.errorBuilding)
return
}
p.allowedCount = c
} else {
p.allowedCount = 1
}
// Determine the number of existing allocations that are using a property
// value
p.populateExisting(constraint)
// Populate the proposed when setting the constraint. We do this because
@ -80,6 +102,7 @@ func (p *propertySet) SetTGConstraint(constraint *structs.Constraint, taskGroup
// eviction and then select. This means the plan has an eviction before a
// single select has finished.
p.PopulateProposed()
}
// populateExisting is a helper shared when setting the constraint to populate
@ -115,8 +138,8 @@ func (p *propertySet) populateExisting(constraint *structs.Constraint) {
func (p *propertySet) PopulateProposed() {
// Reset the proposed properties
p.proposedValues = make(map[string]struct{})
p.clearedValues = make(map[string]struct{})
p.proposedValues = make(map[string]uint64)
p.clearedValues = make(map[string]uint64)
// Gather the set of proposed stops.
var stopping []*structs.Allocation
@ -151,7 +174,14 @@ func (p *propertySet) PopulateProposed() {
// Remove any cleared value that is now being used by the proposed allocs
for value := range p.proposedValues {
delete(p.clearedValues, value)
current, ok := p.clearedValues[value]
if !ok {
continue
} else if current == 0 {
delete(p.clearedValues, value)
} else if current > 1 {
p.clearedValues[value]--
}
}
}
@ -171,27 +201,40 @@ func (p *propertySet) SatisfiesDistinctProperties(option *structs.Node, tg strin
return false, fmt.Sprintf("missing property %q", p.constraint.LTarget)
}
// both is used to iterate over both the proposed and existing used
// properties
bothAll := []map[string]struct{}{p.existingValues, p.proposedValues}
// Check if the nodes value has already been used.
for _, usedProperties := range bothAll {
// Check if the nodes value has been used
_, used := usedProperties[nValue]
if !used {
continue
// combine the counts of how many times the property has been used by
// existing and proposed allocations
combinedUse := make(map[string]uint64, helper.IntMax(len(p.existingValues), len(p.proposedValues)))
for _, usedValues := range []map[string]uint64{p.existingValues, p.proposedValues} {
for propertyValue, usedCount := range usedValues {
combinedUse[propertyValue] += usedCount
}
// Check if the value has been cleared from a proposed stop
if _, cleared := p.clearedValues[nValue]; cleared {
continue
}
return false, fmt.Sprintf("distinct_property: %s=%s already used", p.constraint.LTarget, nValue)
}
return true, ""
// Go through and discount the combined count when the value has been
// cleared by a proposed stop.
for propertyValue, clearedCount := range p.clearedValues {
combined, ok := combinedUse[propertyValue]
if !ok {
continue
}
// Don't clear below 0.
combinedUse[propertyValue] = helper.Uint64Max(0, combined-clearedCount)
}
usedCount, used := combinedUse[nValue]
if !used {
// The property value has never been used so we can use it.
return true, ""
}
// The property value has been used but within the number of allowed
// allocations.
if usedCount < p.allowedCount {
return true, ""
}
return false, fmt.Sprintf("distinct_property: %s=%s used by %d allocs", p.constraint.LTarget, nValue, usedCount)
}
// filterAllocs filters a set of allocations to just be those that are running
@ -245,7 +288,7 @@ func (p *propertySet) buildNodeMap(allocs []*structs.Allocation) (map[string]*st
// populateProperties goes through all allocations and builds up the used
// properties from the nodes storing the results in the passed properties map.
func (p *propertySet) populateProperties(allocs []*structs.Allocation, nodes map[string]*structs.Node,
properties map[string]struct{}) {
properties map[string]uint64) {
for _, alloc := range allocs {
nProperty, ok := getProperty(nodes[alloc.NodeID], p.constraint.LTarget)
@ -253,7 +296,7 @@ func (p *propertySet) populateProperties(allocs []*structs.Allocation, nodes map
continue
}
properties[nProperty] = struct{}{}
properties[nProperty]++
}
}

4
website/source/api/json-jobs.html.md
View File

@ -537,7 +537,9 @@ The `Constraint` object supports the following keys:
omitted.
- `distinct_property` - If set, the scheduler selects nodes that have a
distinct value of the specified property for each allocation. This can
distinct value of the specified property. The `RTarget` specifies how
many allocations are allowed to share the value of a property. The
`RTarget` must be 1 or greater and if omitted, defaults to 1. This can
be specified as a job constraint which applies the constraint to all
task groups in the job, or as a task group constraint which scopes the
effect to just that group. The constraint may not be specified at the

24
website/source/docs/job-specification/constraint.html.md
View File

@ -75,6 +75,8 @@ all groups (and tasks) in the job.
>=
<
<=
distinct_hosts
distinct_property
regexp
set_contains
version
@ -124,16 +126,18 @@ constraint {
```
- `"distinct_property"` - Instructs the scheduler to select nodes that have a
distinct value of the specified property for each allocation. When specified
as a job constraint, it applies to all groups in the job. When specified as a
group constraint, the effect is constrained to that group. This constraint can
not be specified at the task level. Note that the `value` parameter should be
omitted when using this constraint.
distinct value of the specified property. The `value` parameter specifies how
many allocations are allowed to share the value of a property. The `value`
must be 1 or greater and if omitted, defaults to 1. When specified as a job
constraint, it applies to all groups in the job. When specified as a group
constraint, the effect is constrained to that group. This constraint can not
be specified at the task level.
```hcl
constraint {
operator = "distinct_property"
attribute = "${meta.rack}"
value = "3"
}
```
@ -142,7 +146,8 @@ constraint {
```hcl
constraint {
distinct_property = "${meta.rack}"
distinct_property = "${meta.rack}"
value = "3"
}
```
@ -209,13 +214,14 @@ constraint {
A potential use case of the `distinct_property` constraint is to spread a
service with `count > 1` across racks to minimize correlated failure. Nodes can
be annotated with which rack they are on using [client
metadata][client-metadata] with values
such as "rack-12-1", "rack-12-2", etc. The following constraint would then
assure no two instances of the task group existed on the same rack.
metadata][client-metadata] with values such as "rack-12-1", "rack-12-2", etc.
The following constraint would assure that an individual rack is not running
more than 2 instances of the task group.
```hcl
constraint {
distinct_property = "${meta.rack}"
value = "2"
}
```