[nodeutilization]: actual usage client through kubernetes metrics

README.md

@@ -124,6 +124,8 @@ These are top level keys in the Descheduler Policy that you can use to configure
 | `maxNoOfPodsToEvictPerNode` |`int`| `nil` | maximum number of pods evicted from each node (summed through all strategies) |
 | `maxNoOfPodsToEvictPerNamespace` |`int`| `nil` | maximum number of pods evicted from each namespace (summed through all strategies) |
 | `maxNoOfPodsToEvictTotal` |`int`| `nil` | maximum number of pods evicted per rescheduling cycle (summed through all strategies) |
+| `metricsCollector` |`object`| `nil` | configures collection of metrics for actual resource utilization |
+| `metricsCollector.enabled` |`bool`| `false` | enables kubernetes [metrics server](https://kubernetes-sigs.github.io/metrics-server/) collection |
 
 ### Evictor Plugin configuration (Default Evictor)
 
@@ -158,6 +160,8 @@ nodeSelector: "node=node1" # you don't need to set this, if not set all will be
 maxNoOfPodsToEvictPerNode: 5000 # you don't need to set this, unlimited if not set
 maxNoOfPodsToEvictPerNamespace: 5000 # you don't need to set this, unlimited if not set
 maxNoOfPodsToEvictTotal: 5000 # you don't need to set this, unlimited if not set
+metricsCollector:
+	enabled: true # you don't need to set this, metrics are not collected if not set
 profiles:
   - name: ProfileName
     pluginConfig:
@@ -277,11 +281,13 @@ If that parameter is set to `true`, the thresholds are considered as percentage
 `thresholds` will be deducted from the mean among all nodes and `targetThresholds` will be added to the mean.
 A resource consumption above (resp. below) this window is considered as overutilization (resp. underutilization).
 
-**NOTE:** Node resource consumption is determined by the requests and limits of pods, not actual usage.
+**NOTE:** By default node resource consumption is determined by the requests and limits of pods, not actual usage.
 This approach is chosen in order to maintain consistency with the kube-scheduler, which follows the same
 design for scheduling pods onto nodes. This means that resource usage as reported by Kubelet (or commands
 like `kubectl top`) may differ from the calculated consumption, due to these components reporting
-actual usage metrics. Implementing metrics-based descheduling is currently TODO for the project.
+actual usage metrics. Metrics-based descheduling can be enabled by setting `metricsUtilization.metricsServer` field.
+In order to have the plugin consume the metrics the metric collector needs to be configured as well.
+See `metricsCollector` field at [Top Level configuration](#top-level-configuration) for available options.
 
 **Parameters:**
 
@@ -292,6 +298,9 @@ actual usage metrics. Implementing metrics-based descheduling is currently TODO
 |`targetThresholds`|map(string:int)|
 |`numberOfNodes`|int|
 |`evictableNamespaces`|(see [namespace filtering](#namespace-filtering))|
+|`metricsUtilization`|object|
+|`metricsUtilization.metricsServer`|bool|
+
 
 **Example:**
 
@@ -311,6 +320,8 @@ profiles:
           "cpu" : 50
           "memory": 50
           "pods": 50
+        metricsUtilization:
+          metricsServer: true
     plugins:
       balance:
         enabled:

cmd/descheduler/app/options/options.go

@@ -29,6 +29,7 @@ import (
 	componentbaseconfig "k8s.io/component-base/config"
 	componentbaseoptions "k8s.io/component-base/config/options"
 	"k8s.io/klog/v2"
+	metricsclient "k8s.io/metrics/pkg/client/clientset/versioned"
 
 	"sigs.k8s.io/descheduler/pkg/apis/componentconfig"
 	"sigs.k8s.io/descheduler/pkg/apis/componentconfig/v1alpha1"
@@ -46,6 +47,7 @@ type DeschedulerServer struct {
 
 	Client            clientset.Interface
 	EventClient       clientset.Interface
+	MetricsClient     metricsclient.Interface
 	SecureServing     *apiserveroptions.SecureServingOptionsWithLoopback
 	SecureServingInfo *apiserver.SecureServingInfo
 	DisableMetrics    bool

kubernetes/base/rbac.yaml

@@ -32,6 +32,9 @@ rules:
   resources: ["leases"]
   resourceNames: ["descheduler"]
   verbs: ["get", "patch", "delete"]
+- apiGroups: ["metrics.k8s.io"]
+  resources: ["nodes", "pods"]
+  verbs: ["get", "list"]
 ---
 apiVersion: v1
 kind: ServiceAccount

pkg/api/types.go

@@ -41,6 +41,9 @@ type DeschedulerPolicy struct {
 
 	// MaxNoOfPodsToTotal restricts maximum of pods to be evicted total.
 	MaxNoOfPodsToEvictTotal *uint
+
+	// MetricsCollector configures collection of metrics about actual resource utilization
+	MetricsCollector MetricsCollector
 }
 
 // Namespaces carries a list of included/excluded namespaces
@@ -84,3 +87,10 @@ type PluginSet struct {
 	Enabled  []string
 	Disabled []string
 }
+
+// MetricsCollector configures collection of metrics about actual resource utilization
+type MetricsCollector struct {
+	// Enabled metrics collection from kubernetes metrics.
+	// Later, the collection can be extended to other providers.
+	Enabled bool
+}

pkg/api/v1alpha2/types.go

@@ -40,6 +40,9 @@ type DeschedulerPolicy struct {
 
 	// MaxNoOfPodsToTotal restricts maximum of pods to be evicted total.
 	MaxNoOfPodsToEvictTotal *uint `json:"maxNoOfPodsToEvictTotal,omitempty"`
+
+	// MetricsCollector configures collection of metrics for actual resource utilization
+	MetricsCollector MetricsCollector `json:"metricsCollector,omitempty"`
 }
 
 type DeschedulerProfile struct {
@@ -66,3 +69,10 @@ type PluginSet struct {
 	Enabled  []string `json:"enabled"`
 	Disabled []string `json:"disabled"`
 }
+
+// MetricsCollector configures collection of metrics about actual resource utilization
+type MetricsCollector struct {
+	// Enabled metrics collection from kubernetes metrics.
+	// Later, the collection can be extended to other providers.
+	Enabled bool `json:"enabled"`
+}

pkg/descheduler/client/client.go

@@ -21,14 +21,15 @@ import (
 
 	clientset "k8s.io/client-go/kubernetes"
 	componentbaseconfig "k8s.io/component-base/config"
+	metricsclient "k8s.io/metrics/pkg/client/clientset/versioned"
 
 	// Ensure to load all auth plugins.
 	_ "k8s.io/client-go/plugin/pkg/client/auth"
 	"k8s.io/client-go/rest"
 	"k8s.io/client-go/tools/clientcmd"
 )
 
-func CreateClient(clientConnection componentbaseconfig.ClientConnectionConfiguration, userAgt string) (clientset.Interface, error) {
+func createConfig(clientConnection componentbaseconfig.ClientConnectionConfiguration, userAgt string) (*rest.Config, error) {
 	var cfg *rest.Config
 	if len(clientConnection.Kubeconfig) != 0 {
 		master, err := GetMasterFromKubeconfig(clientConnection.Kubeconfig)
@@ -56,9 +57,28 @@ func CreateClient(clientConnection componentbaseconfig.ClientConnectionConfigura
 		cfg = rest.AddUserAgent(cfg, userAgt)
 	}
 
+	return cfg, nil
+}
+
+func CreateClient(clientConnection componentbaseconfig.ClientConnectionConfiguration, userAgt string) (clientset.Interface, error) {
+	cfg, err := createConfig(clientConnection, userAgt)
+	if err != nil {
+		return nil, fmt.Errorf("unable to create config: %v", err)
+	}
+
 	return clientset.NewForConfig(cfg)
 }
 
+func CreateMetricsClient(clientConnection componentbaseconfig.ClientConnectionConfiguration, userAgt string) (metricsclient.Interface, error) {
+	cfg, err := createConfig(clientConnection, userAgt)
+	if err != nil {
+		return nil, fmt.Errorf("unable to create config: %v", err)
+	}
+
+	// Create the metrics clientset to access the metrics.k8s.io API
+	return metricsclient.NewForConfig(cfg)
+}
+
 func GetMasterFromKubeconfig(filename string) (string, error) {
 	config, err := clientcmd.LoadFromFile(filename)
 	if err != nil {