Assign Pod to Node

Assign Pod to Node

Node Selector

You can configure pod to run on particular node by using node label along with nodeSelector

Deploy backend application and scale to 5 pods

oc new-project demo
oc apply -f manifests/backend-v1.yaml -n demo
oc scale deployment backend-v1 --replicas=5 -n demo

Check that 5 pods is running on which worker nodes

watch oc get pods -o 'custom-columns=Name:.metadata.name,PHASE:.status.phase,NODE:.spec.nodeName' -n demo

Sample output

  Name                        PHASE     NODE
  backend-v1-b564ff66-6spph   Running   ip-10-0-XXX-179.us-east-2.compute.internal
  backend-v1-b564ff66-dh77c   Running   ip-10-0-XXX-101.us-east-2.compute.internal
  backend-v1-b564ff66-dtkjn   Running   ip-10-0-XXX-179.us-east-2.compute.internal
  backend-v1-b564ff66-n7kr4   Running   ip-10-0-XXX-121.us-east-2.compute.internal
  backend-v1-b564ff66-thhqv   Running   ip-10-0-XXX-121.us-east-2.compute.internal

Let's say we want to run backend app is belong to project app-x and project app-x need to run on node 179 only then we'll label node 179 with label app-x
```
oc label node ip-10-0-XXX-179.us-east-2.compute.internal app-x=''
```

Add nodeSelector to backend-v1 deployment Remark:

You can use another shell/terminal to check status of backend-v1's pods with previously watch command

sed is use for set replicas to 5.

cat manifests/backend-v1-with-node-selector.yaml | sed s/replicas:\ 1/replicas:\ 5/g | oc apply -n demo -f -

Sample output from watch command

Name                          PHASE     NODE
backend-v1-786cd59759-bcmpx   Running   ip-10-0-XXX-179.us-east-2.compute.internal
backend-v1-786cd59759-dkgxp   Pending   ip-10-0-XXX-179.us-east-2.compute.internal
backend-v1-786cd59759-lpnwq   Pending   ip-10-0-XXX-179.us-east-2.compute.internal
backend-v1-786cd59759-vlqp2   Running   ip-10-0-XXX-179.us-east-2.compute.internal
backend-v1-786cd59759-x4nlb   Running   ip-10-0-XXX-179.us-east-2.compute.internal
backend-v1-b564ff66-dh77c     Running   ip-10-0-XXX-101.us-east-2.compute.internal
backend-v1-b564ff66-thhqv     Running   ip-10-0-XXX-121.us-east-2.compute.internal

When finished all pods will be run on node 179

Name                          PHASE     NODE
backend-v1-786cd59759-bcmpx   Running   ip-10-0-XXX-179.us-east-2.compute.internal
backend-v1-786cd59759-dkgxp   Running   ip-10-0-XXX-179.us-east-2.compute.internal
backend-v1-786cd59759-lpnwq   Running   ip-10-0-XXX-179.us-east-2.compute.internal
backend-v1-786cd59759-vlqp2   Running   ip-10-0-XXX-179.us-east-2.compute.internal
backend-v1-786cd59759-x4nlb   Running   ip-10-0-XXX-179.us-east-2.compute.internal

Check backend-v1 deployment with nodeAffinity under template

  spec:
    affinity:
      nodeAffinity:
        requiredDuringSchedulingIgnoredDuringExecution:
          nodeSelectorTerms:
          - matchExpressions:
            - key: app-x
              operator: Exists

Taints and Tolerations

Taint is proporty of nodes that allow only pod with toleration can be scheduled to run on that particular node.

Let's say we want to allow only project app-x to run on node 179 then we will taint node 179
```
oc adm taint node ip-10-0-248-179.us-east-2.compute.internal app-x='':NoSchedule
```

Taint is not effect pods those already scheduled then we will force backend-v1 to create all pods again

oc delete pods --all -n demo

Pods cannot schedule because there is no toleration in deployment

Name                          PHASE     NODE
backend-v1-786cd59759-79jmh   Pending   <none>
backend-v1-786cd59759-gnwg7   Pending   <none>
backend-v1-786cd59759-lc4jr   Pending   <none>
backend-v1-786cd59759-lgk8r   Pending   <none>
backend-v1-786cd59759-vcd22   Pending   <none>

Check Events in OpenShift Console

Add toleration to backend-v1 deployment

cat manifests/backend-v1-with-node-selector-and-toleration.yaml|sed s/replicas:\ 1/replicas:\ 5/g | oc apply -n demo -f -

When finished all pods will be run on node 179

Name                          PHASE     NODE
backend-v1-647db46bfc-868w6   Running   ip-10-0-XXX-179.us-east-2.compute.internal
backend-v1-647db46bfc-krzvs   Running   ip-10-0-XXX-179.us-east-2.compute.internal
backend-v1-647db46bfc-nssqz   Running   ip-10-0-XXX-179.us-east-2.compute.internal
backend-v1-647db46bfc-qhvws   Running   ip-10-0-XXX-179.us-east-2.compute.internal
backend-v1-647db46bfc-vnl5l   Running   ip-10-0-XXX-179.us-east-2.compute.internal

Check backend-v1 deployment with nodeAffinity under template

    tolerations:
    - effect: NoSchedule
      key: app-x
      operator: Exists

Remove node label and toleration

Following commands show how to remove node label and toleration

oc label node ip-10-0-XXX-179.us-east-2.compute.internal app-x-
oc adm taint nodes ip-10-0-XXX-179.us-east-2.compute.internal app-x='':NoSchedule-

Assign pod to node

Assign Pod to Node

Node Selector

Taints and Tolerations

Remove node label and toleration

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