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Anti-Node-Affinity.md

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Anti-Node Affinity ?

  • Some scenarios require that you don’t use one or more nodes except for particular pods. Think of the nodes that host your monitoring application.
  • Those nodes shouldn’t have many resources due to the nature of their role. Thus, if other pods than those which have the monitoring app are scheduled to those nodes, they hurt monitoring and also degrades the application they are hosting.
  • In such a case, you need to use node anti-affinity to keep pods away from a set of nodes.

Steps

git clone https://github.com/collabnix/dockerlabs
cd dockerlabs/kubernetes/workshop/Scheduler101/
kubectl label nodes node2 mynode=worker-1
kubectl label nodes node3 mynode=worker-3
kubectl apply -f pod-anti-node-affinity.yaml

Viewing Your Pods

[node1 Scheduler101]$ kubectl get pods --output=wide
NAME    READY   STATUS    RESTARTS   AGE     IP          NODE    NOMINATED NODE   READINESS GATES
nginx   1/1     Running   0          2m37s   10.44.0.1   node2   <none>           <none>

Get nodes label detail

[node1 Scheduler101]$ kubectl get nodes --show-labels | grep mynode
node2   Ready    <none>   166m   v1.14.9   beta.kubernetes.io/arch=amd64,beta.kubernetes.io/os=linux,kubernetes.io/arch=amd64,kubernetes.io/hostname=node2,kubernetes.io/os=linux,mynode=worker-1,role=dev
node3   Ready    <none>   165m   v1.14.9   beta.kubernetes.io/arch=amd64,beta.kubernetes.io/os=linux,kubernetes.io/arch=amd64,kubernetes.io/hostname=node3,kubernetes.io/os=linux,mynode=worker-3

Get pod describe

[node1 Scheduler101]$ kubectl describe pods nginx
Name:               nginx
Namespace:          default
Priority:           0
PriorityClassName:  <none>
Node:               node2/192.168.0.17
Start Time:         Mon, 30 Dec 2019 19:02:46 +0000
Labels:             <none>
Annotations:        kubectl.kubernetes.io/last-applied-configuration:
                      {"apiVersion":"v1","kind":"Pod","metadata":{"annotations":{},"name":"nginx","namespace":"default"},"spec":{"affinity":{"nodeAffinity":{"re...
Status:             Running
IP:                 10.44.0.1
Containers:
  nginx:
    Container ID:   docker://2bdc20d79c360e1cd857eeb9bbb9424c726b2133e78f25bf4587e0befe3fbcc7
    Image:          nginx
    Image ID:       docker-pullable://nginx@sha256:b2d89d0a210398b4d1120b3e3a7672c16a4ba09c2c4a0395f18b9f7999b768f2
    Port:           <none>
    Host Port:      <none>
    State:          Running
      Started:      Mon, 30 Dec 2019 19:03:07 +0000
    Ready:          True
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-qpgxq (ro)
Conditions:
  Type              Status
  Initialized       True
  Ready             True
  ContainersReady   True
  PodScheduled      True
Volumes:
  default-token-qpgxq:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-qpgxq
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type    Reason     Age   From               Message
  ----    ------     ----  ----               -------
  Normal  Scheduled  60s   default-scheduler  Successfully assigned default/nginx to node2
  Normal  Pulling    56s   kubelet, node2     Pulling image "nginx"
  Normal  Pulled     54s   kubelet, node2     Successfully pulled image "nginx"
  Normal  Created    40s   kubelet, node2     Created container nginx
  Normal  Started    39s   kubelet, node2     Started container nginx
  • Adding another key to the matchExpressions with the operator NotIn will avoid scheduling the nginx pods on any node labelled worker-1.

Step Cleanup

Finally you can clean up the resources you created in your cluster:

kubectl delete -f pod-anti-node-affinity.yaml

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