descheduler规则
`karmada-descheduler` 定期检测所有部署，通常是每2分钟一次，并确定目标调度集群中无法调度的副本数量。它通过调用 `karmada-scheduler-estimator` 来完成这个过程。如果发现无法调度的副本，它将通过减少 `spec.clusters` 的配置来将它们驱逐出去。这个操作会触发 `karmada-scheduler` 基于当前情况进行“规模调度”。
需要注意的是，只有在将副本调度策略设置为动态划分时，这个驱逐和重新调度的过程才会生效。这种策略允许根据可用资源将副本动态分配到不同的集群中。通过定期检查集群的状态和资源可用性，Karmada可以调整副本的放置位置，以确保资源利用的高效性和系统稳定性。
前提条件
确保所有k8s成员加入到karmada当中且karmada-descheduler加入到karmada-host中如图所示
测试
模拟缺乏资源而导致调度失败，创建俩个nginx副本将他们放到俩个成员集群中
```
root@karmada-cluster01:/home/karmada-teaching/descheduler# cat pp-deploy-nginx-descheduler.yaml
apiVersion: policy.karmada.io/v1alpha1
kind: PropagationPolicy
metadata:
name: nginx-descheduler-propagation
spec:
resourceSelectors:
- apiVersion: apps/v1
kind: Deployment
name: nginx-descheduler
placement:
clusterAffinity:
clusterNames:
- cluster1
- cluster2
replicaScheduling:
replicaDivisionPreference: Weighted
replicaSchedulingType: Divided
weightPreference:
dynamicWeight: AvailableReplicas
---
apiVersion: apps/v1
kind: Deployment
metadata:
name: nginx-descheduler
labels:
app: nginx
spec:
replicas: 3
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- image: 10.250.2.118:18000/library/nginx:latest
name: nginx
```
kubectl apply -f pp-deploy-nginx-descheduler.yaml -n karmada --kubeconfig ~/kube-karmada
propagationpolicy.policy.karmada.io/nginx-descheduler-propagation configured
deployment.apps/nginx-descheduler configured
此时都在cluster01上 现在将cluster集群停止调度
root@karmada-cluster01:/home/karmada-teaching/descheduler# kubectl --kubeconfig ~/.kube/21config cordon k8s-cluster1-node2
node/k8s-cluster1-node2 cordoned
root@karmada-cluster01:/home/karmada-teaching/descheduler# kubectl --kubeconfig ~/.kube/21config cordon k8s-cluster1-node1
node/k8s-cluster1-node1 cordoned
root@karmada-cluster01:/home/karmada-teaching/descheduler# kubectl --kubeconfig ~/.kube/21config cordon k8s-cluster01
node/k8s-cluster01 cordoned删除nginx pod
root@karmada-cluster01:/home/karmada-teaching/descheduler# kubectl --kubeconfig ~/.kube/21config delete pod -l app=nginx -n karmada
pod "nginx-descheduler-7864466765-fgqsc" deleted
pod "nginx-descheduler-7864466765-lhvnr" deleted
pod "nginx-descheduler-7864466765-mbh4n" deleted
```
此时集群1的po状态
```
root@k8s-cluster1-master:/home/k8s# kubectl get po -n karmada -owide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
nginx-descheduler-7864466765-b4h4l 0/1 Pending 0 18s <none> <none> <none> <none>
nginx-descheduler-7864466765-cvx4k 0/1 Pending 0 18s <none> <none> <none> <none>
nginx-descheduler-7864466765-xr22g 0/1 Pending 0 18s <none> <none> <none> <none>
```大概等5-7分钟就会从cluster1到cluster2当当中
已经调度到另外集群当中
