Static Overcommitment

Static resource overcommitment applys a static overcommit ratio to the overcommit node pool.

Installation

Prerequisite

  • Katalyst >= v0.4.0
  • A running kubernetes cluster

Install Katalyst resource overcommitment

helm repo add kubewharf https://kubewharf.github.io/charts
helm install overcommit -n katalyst-system --create-namespace kubewharf/katalyst-overcommit --set katalyst-agent.customArgs.sysadvisor-plugins="-overcommit-aware"

Use static resource overcommitment

  1. Label the nodes we apply resource overcommitment to
kubectl label node worker worker2 worker3 katalyst.kubewharf.io/overcommit_node_pool=overcommit-demo
  1. Create a deployment with 20 replicas
kubectl create -f - <<EOF
kind: Deployment
apiVersion: apps/v1
metadata:
  name: busybox-deployment-overcommit
spec:
  replicas: 20
  selector:
    matchLabels:
      app: busybox
  template:
    metadata:
      labels:
        app: busybox
    spec:
      affinity:
        nodeAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
            nodeSelectorTerms:
            - matchExpressions:
              - key: katalyst.kubewharf.io/overcommit_node_pool
                operator: In
                values:
                - overcommit-demo
      containers:
      - name: busybox
        image: busybox
        command: ["sleep", "36000"]
        resources:
          requests:
            cpu: "1500m"
            memory: "1Gi"
EOF
  1. Check the running status of the pods
kubectl get pod -o wide |grep busybox-deployment-overcommit |awk '{print $3}' |sort |uniq -c

Since each pod request for 1500m of CPU millicores and 1Gi of memory, and we only have 3 node with 4 CPU cores and 8Gi memory each. Most of the pods will be in pending status.

 14 Pending
  6 Running

However, all of the busybox containers are executing sleep 36000 which barely cost you any CPU time, and hence very low overall resource usage.

  1. Configure resource overcommitment, and set the overcommitRatio of both CPU and memory to 2.5
kubectl create -f - <<EOF
apiVersion: overcommit.katalyst.kubewharf.io/v1alpha1
kind: NodeOvercommitConfig
metadata:
  name: overcommit-demo
spec:
  nodeOvercommitSelectorVal: overcommit-demo
  resourceOvercommitRatio:
    cpu: "2.5"
    memory: "2.5"
EOF

This essentially means that Katalyst oversells node resource to allow more pods to be scheduled. If we take a look at the node annotation and status, we can see the orignial and the new allocatable/capacity resource.

apiVersion: v1
kind: Node
metadata:
  annotations:
    katalyst.kubewharf.io/cpu_overcommit_ratio: "2.5"
    katalyst.kubewharf.io/memory_overcommit_ratio: "2.5"
    katalyst.kubewharf.io/original_allocatable_cpu: "4"
    katalyst.kubewharf.io/original_allocatable_memory: 8151352Ki
    katalyst.kubewharf.io/original_capacity_cpu: "4"
    katalyst.kubewharf.io/original_capacity_memory: 8151352Ki
  labels:
    katalyst.kubewharf.io/overcommit_node_pool: overcommit-demo
  name: kind-worker
status:
  allocatable:
    cpu: "10"
    memory: 20378380Ki
  capacity:
    cpu: "10"
    memory: 20378380Ki
    ...
  1. Check the running status of the pods again
kubectl get pod -o wide |grep busybox-deployment-overcommit |awk '{print $3}' |sort |uniq -c

We can verify that more pods are able to get scheduled.

   2 Pending
  18 Running
Last modified May 10, 2024 : Merge pull request #10 from pendoragon/doc (cd3c1fa)