panchalhimself

Scheduling pods in kubernetes

20 June 2023

Scheduling: assigning pods to the nodes. scheduler manages the pods scheduling.

Primarily resource requests and node resource availability is checked by the kubernetes scheduler before scheduling the pod.

nodeSelector

limit which node pods can be scheduled.

uses node lables.

example of node label :-

kubectl label nodes NODE_NAME LABEL_KEY=LABEL_KEY_VALUE

kubectl label node db1 noddy=db1

output of the label being assigned.

Now we have to create another label this time on node db2 because db1 node is control node and pods dont get assigned to it by default.

kubectl label node db2 noddyness=db2

nginx-nodeselector.yaml

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx-nodeselector
  name: nginx-nodeselector
spec:
  nodeSelector:
   noddyness: db2
  containers:
  - image: nginx
    name: nginx-nodeselector
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}

nodeName

bypass scheduling and direct association of pods to a particular node.

nginx-nodename.yaml

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx-nodeselector
  name: nginx-nodeselector
spec:
  nodeName: db3
  containers:
  - image: nginx
    name: nginx-nodeselector
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}

Need to be familiar with the nodeSelector and nodeName blocks.

They are defined under the Pod spec

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