Version: v1.3

Eviction Strategy base on CPU Satisfaction

Introduction

Koordinator supports CPU Suppress strategy, which is used for limiting the available CPU Cores of low-priority Pods (BE) according to the usage of high-priority Pods (LS) under during co-location. When the resource usage of LS Pods increases, Koordlet will reduce the CPU cores that can be used by BE Pods. However, when the LS Pod utilization increases suddenly, large number of BE Pods could be suppressed on small number of CPUs, resulting in the low resource satisfaction of BE pods, moreover, there might be some additional competition on kernel resources.

In fact, most BE pods are batch computing type, which have well failover abilities, and the eviction is acceptable for them since they can retry with better resource quality on other nodes. Koordlet provides an eviction strategy based on CPU resource satisfaction. When the utilization and resource satisfaction exceed the threshold at the same time, pods with lower priority and higher CPU utilization will be evicted first until the CPU satisfaction has returned above the threshold.

Prerequisite

Please make sure Koordinator components are correctly installed in your cluster. If not, please refer to Installation. Batch resource overcommitment and cpu suppress strategy must be enabled first, see this manual for more details.

Component	Version Requirement
Kubernetes	≥v1.18
koordinator	≥v0.3.0

The eviction strategy is provided by Koordlet, which is disabled by default in feature-gate. Please make sure the BECPUEvict=true field has been added in the -feature-gates arguments of Koordlet as the example。

Use Eviction Strategy base on CPU Satisfaction

Create a configmap.yaml file based on the following ConfigMap content:

#ConfigMap slo-controller-config example。
apiVersion: v1
kind: ConfigMap
metadata:
  name: slo-controller-config # name should be set as the configuration of koord-manager, e.g. ack-slo-config 
  namespace: koordinator-system # namespace should be set as the configuration of installation, e.g. kube-system
data:
  # enable the eviction strategy base on CPU satisfaction
  resource-threshold-config: |
    {
      "clusterStrategy": {
        "enable": true,
        "cpuEvictBESatisfactionLowerPercent": 60,
        "cpuEvictBESatisfactionUpperPercent": 80,
        "cpuEvictBEUsageThresholdPercent": 90,
        "CPUEvictTimeWindowSeconds": 60
      }
    }

Configuration item	Parameter	Valid values	Description
`enable`	Boolean	true; false	true：enable the eviction.; false(default): disable the eviction.
`cpuEvictBESatisfactionLowerPercent`	Int	0~60	eviction threshold percent of BE CPU satisfaction. BE pods will be evicted if the satisfaction less than the threshold.
`cpuEvictBESatisfactionUpperPercent`	Int	cpuEvictBESatisfactionLowerPercent~100	threshold percent of BE CPU satisfaction. eviction will be stopped if the satisfaction greater than the threshold.
`cpuEvictBEUsageThresholdPercent`	Int	0~100	threshold of BE CPU utilization. Pods will be evicted if the BE utilization under the suppressed CPU greater than the threshold. default value is 90.
`cpuEvictTimeWindowSeconds`	Int	>=2	time window by seconds during calculating the CPU satisfaction and BE CPU utilization.

Check whether a ConfigMap named slo-controller-config exists in the koordinator-system namespace.

If a ConfigMap named slo-controller-config exists, we commend that you run the kubectl patch command to update the ConfigMap. This avoids changing other settings in the ConfigMap.
```
kubectl patch cm -n koordinator-system slo-controller-config --patch "$(cat configmap.yaml)"
```
If no ConfigMap named slo-controller-config exists, run the kubectl patch command to create a ConfigMap named ack-slo-config:
```
kubectl apply -f configmap.yaml
```

Create a file named be-pod-demo.yaml based on the following YAML content:

apiVersion: v1
kind: Pod
metadata:
  name: be-pod-demo
  labels:
    koordinator.sh/qosClass: 'BE' # set Pod QoS as BE
spec:
  containers:
    - args:
        - '-c'
        - '4'
        - '--vm'
        - '1'
      command:
        - stress
      image: polinux/stress
      imagePullPolicy: Always
      name: stress
      resources:
        limits:
          kubernetes.io/batch-cpu: 4k
          kubernetes.io/batch-memory: 4Gi
        requests:
          kubernetes.io/batch-cpu: 4k
          kubernetes.io/batch-memory: 4Gi
  restartPolicy: Always
  schedulerName: default-scheduler
  # priorityClassName is required when ColocationProfile enabled (default).
  priorityClassName: koord-batch

Run the following command to deploy the be-pod-demo pod in the cluster:
```
kubectl apply -f be-pod-demo.yaml
```

Run the following command to check the be-pod-demo pod in Running state:

$ kubectl get pod be-pod-demo
NAME          READY   STATUS    RESTARTS   AGE
be-pod-demo   1/1     Running   0          7s

Run the following command through stress tool make sure the memory usage of node is above the threshold config, and the argument --cpu means the process will consume 10 cores, this should be adjusted according to the node capacity.
```
$ stress --cpu 1 --vm 1 --vm-bytes 10G --vm-keep
```

Check the running state of be-pod-demo, then you can find the be-pod-demo pod is not exist, and the eviction information can be found in events.

$ kubectl get pod be-pod-demo
Error from server (NotFound): pods "be-pod-demo" not found

$ kubectl get event
LAST SEEN   TYPE      REASON            OBJECT              MESSAGE
44s         Normal    Killing           pod/be-pod-demo                     Stopping container stress
44s         Warning   evictPodSuccess   ${your-pod-object}   evict Pod:be-pod-demo, reason: EvictPodByBECPUSatisfaction, message: killAndEvictBEPodsRelease for node(${your-node-id}), need realase CPU : 1200

Eviction Strategy base on CPU Satisfaction

Introduction​

Prerequisite​

Use Eviction Strategy base on CPU Satisfaction​

Introduction

Prerequisite

Use Eviction Strategy base on CPU Satisfaction