Working nodeFit feature

README.md

@@ -44,6 +44,7 @@ Table of Contents
   - [Namespace filtering](#namespace-filtering)
   - [Priority filtering](#priority-filtering)
   - [Label filtering](#label-filtering)
+  - [Node Fit filtering](#node-fit-filtering)
 - [Pod Evictions](#pod-evictions)
   - [Pod Disruption Budget (PDB)](#pod-disruption-budget-pdb)
 - [Metrics](#metrics)
@@ -157,6 +158,7 @@ should include `ReplicaSet` to have pods created by Deployments excluded.
 |`namespaces`|(see [namespace filtering](#namespace-filtering))|
 |`thresholdPriority`|int (see [priority filtering](#priority-filtering))|
 |`thresholdPriorityClassName`|string (see [priority filtering](#priority-filtering))|
+|`nodeFit`|bool (see [node fit filtering](#node-fit-filtering))|
 
 **Example:**
 ```yaml
@@ -204,6 +206,7 @@ strategy evicts pods from `overutilized nodes` (those with usage above `targetTh
 |`numberOfNodes`|int|
 |`thresholdPriority`|int (see [priority filtering](#priority-filtering))|
 |`thresholdPriorityClassName`|string (see [priority filtering](#priority-filtering))|
+|`nodeFit`|bool (see [node fit filtering](#node-fit-filtering))|
 
 **Example:**
 
@@ -253,6 +256,7 @@ node.
 |`thresholdPriorityClassName`|string (see [priority filtering](#priority-filtering))|
 |`namespaces`|(see [namespace filtering](#namespace-filtering))|
 |`labelSelector`|(see [label filtering](#label-filtering))|
+|`nodeFit`|bool (see [node fit filtering](#node-fit-filtering))|
 
 **Example:**
 
@@ -291,6 +295,7 @@ podA gets evicted from nodeA.
 |`thresholdPriorityClassName`|string (see [priority filtering](#priority-filtering))|
 |`namespaces`|(see [namespace filtering](#namespace-filtering))|
 |`labelSelector`|(see [label filtering](#label-filtering))|
+|`nodeFit`|bool (see [node fit filtering](#node-fit-filtering))|
 
 **Example:**
 
@@ -320,6 +325,7 @@ and will be evicted.
 |`thresholdPriorityClassName`|string (see [priority filtering](#priority-filtering))|
 |`namespaces`|(see [namespace filtering](#namespace-filtering))|
 |`labelSelector`|(see [label filtering](#label-filtering))|
+|`nodeFit`|bool (see [node fit filtering](#node-fit-filtering))|
 
 **Example:**
 
@@ -348,6 +354,7 @@ include soft constraints.
 |`thresholdPriority`|int (see [priority filtering](#priority-filtering))|
 |`thresholdPriorityClassName`|string (see [priority filtering](#priority-filtering))|
 |`namespaces`|(see [namespace filtering](#namespace-filtering))|
+|`nodeFit`|bool (see [node fit filtering](#node-fit-filtering))|
 
 **Example:**
 
@@ -379,6 +386,7 @@ which determines whether init container restarts should be factored into that ca
 |`thresholdPriority`|int (see [priority filtering](#priority-filtering))|
 |`thresholdPriorityClassName`|string (see [priority filtering](#priority-filtering))|
 |`namespaces`|(see [namespace filtering](#namespace-filtering))|
+|`nodeFit`|bool (see [node fit filtering](#node-fit-filtering))|
 
 **Example:**
 
@@ -551,6 +559,49 @@ strategies:
           - {key: environment, operator: NotIn, values: [dev]}
 ```
 
+
+### Node Fit filtering
+
+The following strategies accept a `nodeFit` boolean parameter which can optimize descheduling:
+* `RemoveDuplicates`
+* `LowNodeUtilization`
+* `RemovePodsViolatingInterPodAntiAffinity`
+* `RemovePodsViolatingNodeAffinity`
+* `RemovePodsViolatingNodeTaints`
+* `RemovePodsViolatingTopologySpreadConstraint`
+* `RemovePodsHavingTooManyRestarts`
+
+ If set to `true` the descheduler will consider whether or not the pods that meet eviction criteria will fit on other nodes before evicting them. If a pod cannot be rescheduled to another node, it will not be evicted. Currently the following criteria are considered when setting `nodeFit` to `true`:
+- A `nodeSelector` on the pod
+- Any `Tolerations` on the pod and any `Taints` on the other nodes
+- `nodeAffinity` on the pod
+- Whether any of the other nodes are marked as `unschedulable`
+
+E.g.
+
+```yaml
+apiVersion: "descheduler/v1alpha1"
+kind: "DeschedulerPolicy"
+strategies:
+  "LowNodeUtilization":
+     enabled: true
+     params:
+       nodeResourceUtilizationThresholds:
+         thresholds:
+           "cpu" : 20
+           "memory": 20
+           "pods": 20
+         targetThresholds:
+           "cpu" : 50
+           "memory": 50
+           "pods": 50
+        nodeFit: true
+```
+
+Note that node fit filtering references the current pod spec, and not that of it's owner. Thus, if the pod is owned by a ReplicationController (and that ReplicationController was modified recently), the pod may be running with an outdated spec, which the descheduler will reference when determining node fit. This is expected behavior as the descheduler is a "best-effort" mechanism. 
+
+Using Deployments instead of ReplicationControllers provides an automated rollout of pod spec changes, therefore ensuring that the descheduler has an up-to-date view of the cluster state.
+
 ## Pod Evictions
 
 When the descheduler decides to evict pods from a node, it employs the following general mechanism:

pkg/api/types.go

@@ -80,6 +80,7 @@ type StrategyParameters struct {
 	ThresholdPriority                 *int32
 	ThresholdPriorityClassName        string
 	LabelSelector                     *metav1.LabelSelector
+	NodeFit                           bool
 }
 
 type Percentage float64

pkg/api/v1alpha1/types.go

@@ -78,6 +78,7 @@ type StrategyParameters struct {
 	ThresholdPriority                 *int32                             `json:"thresholdPriority"`
 	ThresholdPriorityClassName        string                             `json:"thresholdPriorityClassName"`
 	LabelSelector                     *metav1.LabelSelector              `json:"labelSelector"`
+	NodeFit                           bool                               `json:"nodeFit"`
 }
 
 type Percentage float64

pkg/descheduler/evictions/evictions.go

@@ -32,6 +32,7 @@ import (
 	"k8s.io/client-go/tools/record"
 	"k8s.io/klog/v2"
 	"sigs.k8s.io/descheduler/metrics"
+	nodeutil "sigs.k8s.io/descheduler/pkg/descheduler/node"
 	podutil "sigs.k8s.io/descheduler/pkg/descheduler/pod"
 	"sigs.k8s.io/descheduler/pkg/utils"
 
@@ -47,6 +48,7 @@ type nodePodEvictedCount map[*v1.Node]int
 
 type PodEvictor struct {
 	client                  clientset.Interface
+	nodes                   []*v1.Node
 	policyGroupVersion      string
 	dryRun                  bool
 	maxPodsToEvictPerNode   int
@@ -74,6 +76,7 @@ func NewPodEvictor(
 
 	return &PodEvictor{
 		client:                  client,
+		nodes:                   nodes,
 		policyGroupVersion:      policyGroupVersion,
 		dryRun:                  dryRun,
 		maxPodsToEvictPerNode:   maxPodsToEvictPerNode,
@@ -164,6 +167,7 @@ func evictPod(ctx context.Context, client clientset.Interface, pod *v1.Pod, poli
 
 type Options struct {
 	priority *int32
+	nodeFit  bool
 }
 
 // WithPriorityThreshold sets a threshold for pod's priority class.
@@ -175,6 +179,16 @@ func WithPriorityThreshold(priority int32) func(opts *Options) {
 	}
 }
 
+// WithNodeFit sets whether or not to consider taints, node selectors,
+// and pod affinity when evicting. A pod who's tolerations, node selectors,
+// and affinity match a node other than the one it is currently running on
+// is evictable.
+func WithNodeFit(nodeFit bool) func(opts *Options) {
+	return func(opts *Options) {
+		opts.nodeFit = nodeFit
+	}
+}
+
 type constraint func(pod *v1.Pod) error
 
 type evictable struct {
@@ -225,6 +239,14 @@ func (pe *PodEvictor) Evictable(opts ...func(opts *Options)) *evictable {
 			return nil
 		})
 	}
+	if options.nodeFit {
+		ev.constraints = append(ev.constraints, func(pod *v1.Pod) error {
+			if !nodeutil.PodFitsAnyOtherNode(pod, pe.nodes) {
+				return fmt.Errorf("pod does not fit on any other node because of nodeSelector(s), Taint(s), or nodes marked as unschedulable")
+			}
+			return nil
+		})
+	}
 
 	return ev
 }