nodeutilization: separate code responsible for requested resource extraction into a dedicated usage client

Turning a usage client into an interface allows to implement other kinds
of usage clients like actual usage or prometheus based resource
collection.

pkg/framework/plugins/nodeutilization/usageclients.go

@@ -0,0 +1,102 @@
+/*
+Copyright 2024 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package nodeutilization
+
+import (
+	"fmt"
+
+	v1 "k8s.io/api/core/v1"
+	"k8s.io/apimachinery/pkg/api/resource"
+	"k8s.io/klog/v2"
+	utilptr "k8s.io/utils/ptr"
+	nodeutil "sigs.k8s.io/descheduler/pkg/descheduler/node"
+	podutil "sigs.k8s.io/descheduler/pkg/descheduler/pod"
+	"sigs.k8s.io/descheduler/pkg/utils"
+)
+
+type usageClient interface {
+	// Both low/high node utilization plugins are expected to invoke sync right
+	// after Balance method is invoked. There's no cache invalidation so each
+	// Balance is expected to get the latest data by invoking sync.
+	sync(nodes []*v1.Node) error
+	nodeUtilization(node string) map[v1.ResourceName]*resource.Quantity
+	pods(node string) []*v1.Pod
+	podUsage(pod *v1.Pod) (map[v1.ResourceName]*resource.Quantity, error)
+}
+
+type requestedUsageClient struct {
+	resourceNames         []v1.ResourceName
+	getPodsAssignedToNode podutil.GetPodsAssignedToNodeFunc
+
+	_pods            map[string][]*v1.Pod
+	_nodeUtilization map[string]map[v1.ResourceName]*resource.Quantity
+}
+
+var _ usageClient = &requestedUsageClient{}
+
+func newRequestedUsageClient(
+	resourceNames []v1.ResourceName,
+	getPodsAssignedToNode podutil.GetPodsAssignedToNodeFunc,
+) *requestedUsageClient {
+	return &requestedUsageClient{
+		resourceNames:         resourceNames,
+		getPodsAssignedToNode: getPodsAssignedToNode,
+	}
+}
+
+func (s *requestedUsageClient) nodeUtilization(node string) map[v1.ResourceName]*resource.Quantity {
+	return s._nodeUtilization[node]
+}
+
+func (s *requestedUsageClient) pods(node string) []*v1.Pod {
+	return s._pods[node]
+}
+
+func (s *requestedUsageClient) podUsage(pod *v1.Pod) (map[v1.ResourceName]*resource.Quantity, error) {
+	usage := make(map[v1.ResourceName]*resource.Quantity)
+	for _, resourceName := range s.resourceNames {
+		usage[resourceName] = utilptr.To[resource.Quantity](utils.GetResourceRequestQuantity(pod, resourceName).DeepCopy())
+	}
+	return usage, nil
+}
+
+func (s *requestedUsageClient) sync(nodes []*v1.Node) error {
+	s._nodeUtilization = make(map[string]map[v1.ResourceName]*resource.Quantity)
+	s._pods = make(map[string][]*v1.Pod)
+
+	for _, node := range nodes {
+		pods, err := podutil.ListPodsOnANode(node.Name, s.getPodsAssignedToNode, nil)
+		if err != nil {
+			klog.V(2).InfoS("Node will not be processed, error accessing its pods", "node", klog.KObj(node), "err", err)
+			return fmt.Errorf("error accessing %q node's pods: %v", node.Name, err)
+		}
+
+		nodeUsage, err := nodeutil.NodeUtilization(pods, s.resourceNames, func(pod *v1.Pod) (v1.ResourceList, error) {
+			req, _ := utils.PodRequestsAndLimits(pod)
+			return req, nil
+		})
+		if err != nil {
+			return err
+		}
+
+		// store the snapshot of pods from the same (or the closest) node utilization computation
+		s._pods[node.Name] = pods
+		s._nodeUtilization[node.Name] = nodeUsage
+	}
+
+	return nil
+}