Application Scaling Priority Policies

Constraints

• The cluster version must be 1.23.11 or later, 1.25.6 or later, or 1.27.3 or later.
• The Volcano Scheduler add-on (1.12.1 or later) must be installed in a cluster, and the application scaling priority policy function must be enabled.
• By default, the scaling priority takes effect for Deployments (including ReplicaSet).
• To use the scale-out scheduling priority policies, you need to set spec.schedulerName of a workload to volcano or set the default cluster scheduler to volcano. The application scaling priority policy function applies not to workloads with no resource limit and requested resources configured.
• If the default priority policy is used, Volcano Scheduler schedules workloads based on the priorities of yearly/monthly nodes, pay-per-use nodes, and virtual-kubelet nodes (scaling pods to CCI). However, the priorities cannot be fully implemented, because Volcano Scheduler takes scheduling results into account from multiple dimensions rather than just one.
• Volcano Scheduler must balance scheduling performance with scheduling results. When there are a large number of schedulable nodes in a cluster, it selects only some of them for scheduling to ensure scheduling performance and will not find the best global scheduling solution. For details, see Scheduler Performance Tuning. This behavior conflicts with the scaling priority policies. But you can make Volcano Scheduler select all nodes for scheduling by adjusting the proportion of nodes that can be scheduled by Volcano Scheduler.

Overview

After the application scaling priority policy is enabled, the Balancer and BalancerPolicyTemplate CRDs are added to a cluster, and the default scaling priority policy is created. For details, see Applying the Default Application Scaling Priority Policy. Volcano Scheduler obtains the priority of each node based on the BalancerPolicyTemplate CR to control the pod scheduling priority during application scale-out. In addition, it configures the priority during application scale-in based on both Balancer and BalancerPolicyTemplate CRs.

• The BalancerPolicyTemplate CRDs are used to define priority policies. For example, in the default scaling priority policy, the BalancerPolicyTemplate CR assigns the highest priority to yearly/monthly nodes, followed by pay-per-use nodes, and the lowest priority to virtual-kubelet nodes (scaling pods to CCI) by default.

  The BalancerPolicyTemplate CRs cannot be updated.

• The Balancer CRDs are used to declare the application scope of scaling priorities. When creating a Balancer CR, you can specify a workload in a namespace, a specific Deployment, or a specific ReplicaSet as the application scope.

A Balancer CR corresponds to a BalancerPolicyTemplate CR. They work together to determine which priority policies are applied to specific workloads.

In Volcano Scheduler's default scaling priority policy, the BalancerPolicyTemplate CR classifies yearly/monthly nodes, pay-per-use nodes, and virtual-kubelet nodes (scaling pods to CCI) into different priorities. Volcano Scheduler takes these priorities into account during scale-out and preferentially schedules new pods to the yearly/monthly nodes with higher priorities.

Volcano Scheduler applies annotations to pods within the application scope specified by the Balancer CR based on the priorities set by the BalancerPolicyTemplate CR. It may add the following annotations to a pod that meets the conditions:

• openvessel.io/workload-balancer-score: indicates a pod's score, which is higher if the pod is on a high-priority node.
• autoscaling.volcano.sh/dominated-by-balancer: specifies the Balancer CR that controls the current pod. Pods with low scores are preferentially scaled in.

If the existing pods already have the community supported controller.kubernetes.io/pod-deletion-cost annotation added, scale-in will be performed based on the priority defined by this annotation. If two pods have the same value for this annotation, the openvessel.io/workload-balancer-score annotation will be used to determine which pod to scale-in.

Configuring an Application Scaling Priority Policy

1. Install Volcano Scheduler in a cluster and enable the application scaling priority policy. The default scaling priority policy will be created in the cluster.
   1. Obtain a default Balancer CR.

      # kubectl get balancer default-balancer -oyaml
      
      apiVersion: autoscaling.volcano.sh/v1alpha1
      kind: Balancer
      metadata:
        name: default-balancer
      spec:
        balancerPolicyTemplateName: default-balancerpolicytemplate
        targets:
        - namespaceSelector:
            matchExpressions:
              - key: kubernetes.io/metadata.name
                operator: Exists
        weight: 10 

   2. Obtain a default BalancerPolicyTemplate CR.

      # kubectl get balancerpolicytemplate default-balancerpolicytemplate -oyaml
      
      apiVersion: autoscaling.volcano.sh/v1alpha1
      kind: BalancerPolicyTemplate
      metadata:
        name: default-balancerpolicytemplate
      spec:
        policy:
          policyName: Priority
          priorities:
            priorityGroups:
            - priority: 10
              requirements:
              - key: node.cce.io/billing-mode
                operator: In
                values:
                - post-paid
            - priority: 100
              requirements:
              - key: node.cce.io/billing-mode
                operator: In
                values:
                - pre-paid
            - priority: 1
              requirements:
              - key: kubernetes.io/role
                operator: In
                values:
                - virtual-kubelet
                - bursting

   For details about the parameters, see Applying the Default Application Scaling Priority Policy.

2. Deploy a workload and set the number of pods to 1.

   Pods of the current workload are preferentially scheduled to yearly/monthly nodes.

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: balancer-test
     namespace: default
     labels:
       virtual-kubelet.io/burst-to-cci: 'auto'  #If the resources of a cluster are not enough, pods in this cluster can be deployed on CCI.
   spec:
     replicas: 1
     selector:
       matchLabels:
         app: balancer-test
     template:
       metadata:
         labels:
           app: balancer-test
       spec:
         containers:
         - image: nginx:latest
           imagePullPolicy: IfNotPresent
           name: container-1
           resources:
             limits:
               cpu: 250m
               memory: 512Mi
             requests:
               cpu: 250m
               memory: 512Mi
         schedulerName: volcano

3. Increase the number of workload pods to 5.

   Pods of the current workload are preferentially scheduled to yearly/monthly nodes. If there are not enough yearly/monthly nodes, these pods will be preferentially scheduled to pay-per-use nodes. If there are not enough pay-per-use nodes, these pods will be scheduled to virtual-kubelet nodes (scaling pods to CCI).

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: balancer-test
     namespace: default
     labels:
       virtual-kubelet.io/burst-to-cci: 'auto'  #If the resources of a cluster are not enough, pods in this cluster can be deployed on CCI.
   spec:
     replicas: 5
     selector:
       matchLabels:
         app: balancer-test
     template:
       metadata:
         labels:
           app: balancer-test
       spec:
         containers:
         - image: nginx:latest
           imagePullPolicy: IfNotPresent
           name: container-1
           resources:
             limits:
               cpu: 250m
               memory: 512Mi
             requests:
               cpu: 250m
               memory: 512Mi
         schedulerName: volcano

4. View the scores of pods.
   1. Pods on a yearly/monthly node:

      apiVersion: v1
      kind: Pod
      metadata:
        annotations:
          autoscaling.volcano.sh/dominated-by-balancer: default-balancer  #The Balancer CR named default-balancer controls the scaling priority of the current pods.
          openvessel.io/workload-balancer-score: "100" #Priority of the current yearly/monthly node, which also indicates the pods' score
      ...
        nodeName: 192.168.20.100 #A yearly/monthly node

   2. Pods on a pay-per-use node:

      apiVersion: v1
      kind: Pod
      metadata:
        annotations:
          autoscaling.volcano.sh/dominated-by-balancer: default-balancer  #The Balancer CR named default-balancer controls the scaling priority of the current pods.
          openvessel.io/workload-balancer-score "10"  #Priority of the current pay-per-use node, which also indicates the pods' score
          ...
        nodeName: 192.168.20.196 #A pay-per-use node

   3. Pods on a virtual-kubelet node (scaling pods to CCI):

      apiVersion: v1
      kind: Pod
      metadata:
        annotations:
          autoscaling.volcano.sh/dominated-by-balancer: default-balancer  #The Balancer CR named default-balancer controls the scaling priority of the current pods.
          openvessel.io/workload-balancer-score: "1"  #Priority of the current virtual-kubelet node, which also indicates the pods' score
          ...
        nodeName: virtual-kubelet #A virtual-kubelet node

5. Gradually reduce the number of the workload pods.

   Pods on virtual-kubelet nodes (scaling pods to CCI) are deleted first, followed by pods on pay-per-use nodes and those on yearly/monthly nodes.

Applying the Default Application Scaling Priority Policy

When the default application scaling priority policy is used, the following default CRs are present in a cluster:

• A Balancer CR:

  apiVersion: autoscaling.volcano.sh/v1alpha1
  kind: Balancer
  metadata:
    name: default-balancer
  spec:
    balancerPolicyTemplateName: default-balancerpolicytemplate
    targets:
    - namespaceSelector:
        matchExpressions:
          - key: kubernetes.io/metadata.name
            operator: Exists
    weight: 10 

  Table 1 Key parameters of a Balancer CR

  Field	Description	Type	Remarks
  metadata.name	Name	String	This field is mandatory.
  spec. balancerPolicyTemplateName	Name of the priority policy	String	This field is mandatory. The value is the name of the corresponding BalancerPolicyTemplate CR in the cluster.
  spec.targets	Application scope of the priority policy	Slice	This field is mandatory. Example: Applying to applications in the default namespace: spec: targets: - namespaceSelector: matchLabels: kubernetes.io/metadata.name: default Applying to applications in multiple namespaces like default, other, and another: spec: targets: - namespaceSelector: matchExpressions: - key: kubernetes.io/metadata.name operator: In values: - default - other - another Applying to applications in all namespaces: spec: targets: - namespaceSelector: matchExpressions: - key: kubernetes.io/metadata.name operator: Exists Only applying to Deployments which are named in the format of xxx-xxx-xxx: spec: targets: - objectSelectors: - name: xxx-xxx-xxx kind: Deployment Only applying to Deployments which are named in the format of xxx-xxx-xxx and are in the default namespace: spec: targets: - namespaceSelector: matchLabels: kubernetes.io/metadata.name: default objectSelectors: - name: xxx-xxx-xxx kind: Deployment
  spec.weight	Weight of the priority policy	int32	This field is mandatory. When there are multiple Balancer CRs in a cluster, an application may fall within the scope of more than one of them. In such cases, the Balancer CR with the highest weight will be applied.

• A BalancerPolicyTemplate CR:

  apiVersion: autoscaling.volcano.sh/v1alpha1
  kind: BalancerPolicyTemplate
  metadata:
    name: default-balancerpolicytemplate
  spec:
    policy:
      policyName: Priority
      priorities:
        priorityGroups:
        - priority: 10
          requirements:
          - key: node.cce.io/billing-mode
            operator: In
            values:
            - post-paid
        - priority: 100
          requirements:
          - key: node.cce.io/billing-mode
            operator: In
            values:
            - pre-paid
        - priority: 1
          requirements:
          - key: kubernetes.io/role
            operator: In
            values:
            - virtual-kubelet
            - bursting

  Table 2 Key parameters of a BalancerPolicyTemplate CR

  Field	Description	Type	Remarks
  metadata.name	Name	String	This field is mandatory.
  spec.policy	Content of the priority policy	Struct	This field is mandatory.
  spec.policy.policyname	Name of the priority policy	String	This field is mandatory. Only the priority policy named Priority is supported.
  spec.policy.priorities. priorityGroups	Specific priority defined in the priority policy	Slice	This field is mandatory. Example: Setting the priority of a yearly/monthly node to 100: priorityGroups: - priority: 100 requirements: - key: node.cce.io/billing-mode operator: In values: - pre-paid Setting the priority of a pay-per-use node to 10: priorityGroups: - priority: 10 requirements: - key: node.cce.io/billing-mode operator: In values: - post-paid Setting the priority of a virtual-kubelet or bursting node to 1: priorityGroups: - priority: 1 requirements: - key: kubernetes.io/role operator: In values: - virtual-kubelet - bursting

Customizing an Application Scaling Priority Policy

The BalancerPolicyTemplate CRDs are used to define priority policies. If you need to customize an application scaling priority policy, you need to modify the BalancerPolicyTemplate CR.

If there are multiple BalancerPolicyTemplate CRs in a cluster, they will all affect the scaling result. Therefore, if the default scaling priority policy is not in use, run the following command to delete it:

kubectl delete balancerpolicytemplate default-balancerpolicytemplate

Assume that during scale-out, a workload is preferentially scheduled to a node running HCE 2.0 and then to a node running Euler. During scale-in, Volcano Scheduler first deletes the workload pods on the node running Euler and then deletes the pods on the node running HCE 2.0.

1. Write a new BalancerPolicyTemplate CR.

   vim new-balancerpolicytemplate.yaml

   The content is as follows:

   apiVersion: autoscaling.volcano.sh/v1alpha1
   kind: BalancerPolicyTemplate
   metadata:
     name: new-balancerpolicytemplate
   spec:
     policy:
       policyName: Priority
       priorities:
         priorityGroups:
         - priority: 10    # Set the priority of the node running EulerOS to 10.
           requirements:
           - key: os.name  # Label of the Node OS
             operator: In
             values:
             - EulerOS_2.0_SP9x86_64  # The minor version number of the OS may be involved. You can add the minor version number as needed.
         - priority: 100   # Set the priority of the node running HCE 2.0 to 100.
           requirements:
           - key: os.name  # Label of the Node OS
             operator: In
             values:
             - Huawei_Cloud_EulerOS_2.0_x86_64

2. Create a new BalancerPolicyTemplate CR.

   kubectl create -f new-balancerpolicytemplate.yaml

3. Modify default-balancer. You can also create a new Balancer CR as needed.

   kubectl edit balancer default-balancer

   The modified content is as follows:

   apiVersion: autoscaling.volcano.sh/v1alpha1
   kind: Balancer
   metadata:
     name: default-balancer
   spec:
     balancerPolicyTemplateName: new-balancerpolicytemplate
     targets:
     - namespaceSelector:
         matchExpressions:
           - key: kubernetes.io/metadata.name
             operator: Exists
     weight: 10 

4. Check whether the value of openvessel.io/workload-balancer-score in each pod meets the expectation.

   The value of openvessel.io/workload-balancer-score in each pod on the node running EulerOS is set to 10. The value of openvessel.io/workload-balancer-score in each pod on the node running HCE 2.0 is set to 100.

Appendix: Adjusting the Proportion of Nodes That Can Be Scheduled by Volcano Scheduler

kubectl edit deploy volcano-scheduler -nkube-system

The content is as follows:

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: volcano-scheduler
    app.kubernetes.io/managed-by: Helm
    release: cceaddon-volcano
  name: volcano-scheduler
  namespace: kube-system
spec:
  progressDeadlineSeconds: 600
  replicas: 1
  revisionHistoryLimit: 10
  selector:
    matchLabels:
      app: volcano-scheduler
  strategy:
    rollingUpdate:
      maxSurge: 10%
      maxUnavailable: 1
    type: RollingUpdate
  template:
    metadata:
      creationTimestamp: null
      labels:
        app: volcano-scheduler
        release: cceaddon-volcano
    spec:
      affinity:
        podAntiAffinity:
          preferredDuringSchedulingIgnoredDuringExecution:
          - podAffinityTerm:
              labelSelector:
                matchExpressions:
                - key: app
                  operator: In
                  values:
                  - volcano-scheduler
              topologyKey: topology.kubernetes.io/zone
            weight: 100
          requiredDuringSchedulingIgnoredDuringExecution:
          - labelSelector:
              matchExpressions:
              - key: app
                operator: In
                values:
                - volcano-scheduler
            topologyKey: kubernetes.io/hostname
      containers:
      - command:
        - /bin/sh
        - -c
        - /volcano-scheduler --leader-elect=true --lock-object-namespace=kube-system
          --feature-gates=CSIMigrationFlexVolumeFuxi=true,CSIMigrationFlexVolumeFuxiComplete=true,MultiGPUScheduling=true
          --kube-api-qps=200 --alsologtostderr --listen-address=$(MY_POD_IP):8080
          --enable-healthz=true --healthz-address=$(MY_POD_IP):11251 --enable-metrics=true --percentage-nodes-to-find=100
          --scheduler-conf=/volcano.scheduler/default-scheduler.conf -v=3 1>>/var/log/volcano/volcano-scheduler.log

--percentage-nodes-to-find=100 specifies that Volcano Scheduler can find all nodes in a cluster during scheduling selection.