Version: v1.4

Eviction Strategy base on Memory Usage

Introduction

Koordinator supports the dynamic overcommitment from idle resources on node to low-priority Pods as Batch priority. In co-location scenarios, the actual memory resource usage of nodes is constantly changing. For incompressible resources such as memory, high resource usage of node may cause OOM, which results in the high-priority Pod got killed. Koordinator provides an eviction strategy based on the memory usage node. Koordlet will continuously detect the memory usage of node (Total-Available) in second-level granularity. When the resource memory usage of node is high, it will evict low-priority BE Pods to ensure the QoS of high-priority pods until the memory usage of node reduces below to the threshold (evictThreshold). During the eviction process, Pods with lower priority(Pod.Spec.Priority) will be selected first, and if the priority is the same, Pods which consume more memory will be evicted first.

Prerequisite

Please make sure Koordinator components are correctly installed in your cluster. If not, please refer to Installation.

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 BEMemoryEvict=true field has been added in the -feature-gates arguments of Koordlet as the example。

Use Eviction Strategy base on Memory Usage

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 Memory Usage
  resource-threshold-config: |
    {
      "clusterStrategy": {
        "enable": true,
        "memoryEvictThresholdPercent": 70
      }
    }

Configuration item	Parameter	Valid values	Description
`enable`	Boolean	true; false	true：enable the eviction.; false（default）：disable the eviction.
`memoryEvictThresholdPercent`	Int	0~100	eviction threshold percent of node memory usage, default is 70.

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'
        - '1'
        - '--vm'
        - '1'
      command:
        - stress
      image: polinux/stress
      imagePullPolicy: Always
      name: stress
  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 --vm-bytes means the process will consume 10GB memory, 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
46s         Normal    Killing           pod/be-pod-demo     Stopping container stress
48s         Warning   evictPodSuccess   ${your-pod-object}     evict Pod:be-pod-demo, reason: EvictPodByNodeMemoryUsage, message: killAndEvictBEPods for node(${your-node-id}), need to release memory: 8077889699

Eviction Strategy base on Memory Usage

Introduction​

Prerequisite​

Use Eviction Strategy base on Memory Usage​

Introduction

Prerequisite

Use Eviction Strategy base on Memory Usage