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Clarify usage of MaxSkew and WheUnsatisfiable

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Signed-off-by: Aldo Culquicondor <acondor@google.com>
This commit is contained in:
Aldo Culquicondor
2020-05-04 16:57:47 -04:00
parent ffec75da81
commit 883e4860d3
5 changed files with 37 additions and 22 deletions
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17
pkg/apis/core/types.go
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@@ -5176,8 +5176,8 @@ const (
// TopologySpreadConstraint specifies how to spread matching pods among the given topology.
type TopologySpreadConstraint struct {
// MaxSkew describes the degree to which pods may be unevenly distributed.
// It's the maximum permitted difference between the number of matching pods in
// any two topology domains of a given topology type.
// When `whenUnsatisfiable=DoNotSchedule`, it is the maximum permitted difference
// between the number of matching pods in the target topology and the global minimum.
// For example, in a 3-zone cluster, MaxSkew is set to 1, and pods with the same
// labelSelector spread as 1/1/0:
// +-------+-------+-------+
@@ -5189,6 +5189,8 @@ type TopologySpreadConstraint struct {
// scheduling it onto zone1(zone2) would make the ActualSkew(2-0) on zone1(zone2)
// violate MaxSkew(1).
// - if MaxSkew is 2, incoming pod can be scheduled onto any zone.
// When `whenUnsatisfiable=ScheduleAnyway`, it is used to give higher precedence
// to topologies that satisfy it.
// It's a required field. Default value is 1 and 0 is not allowed.
MaxSkew int32
// TopologyKey is the key of node labels. Nodes that have a label with this key
@@ -5199,10 +5201,13 @@ type TopologySpreadConstraint struct {
TopologyKey string
// WhenUnsatisfiable indicates how to deal with a pod if it doesn't satisfy
// the spread constraint.
// - DoNotSchedule (default) tells the scheduler not to schedule it
// - ScheduleAnyway tells the scheduler to still schedule it
// It's considered as "Unsatisfiable" if and only if placing incoming pod on any
// topology violates "MaxSkew".
// - DoNotSchedule (default) tells the scheduler not to schedule it.
// - ScheduleAnyway tells the scheduler to schedule the pod in any location,
// but giving higher precedence to topologies that would help reduce the
// skew.
// A constraint is considered "Unsatisfiable" for an incoming pod
// if and only if every possible node assigment for that pod would violate
// "MaxSkew" on some topology.
// For example, in a 3-zone cluster, MaxSkew is set to 1, and pods with the same
// labelSelector spread as 3/1/1:
// +-------+-------+-------+