Node Selector is the simplest recommended form of node selection constraint.
How does Kubernetes know which is the large node. The key-value pair of size and large are in fact labels assigned to the nodes.
Add lable the nodes
$ kubectl label nodes kubenode01 size=large
node/kubenode01 labeledCreate a pod in the node.
apiVersion: v1
kind: Pod
metadata:
name: apple-pod
labels:
app: apple
type: nginx-server
spec:
containers:
- name: nginx-container
image: nginx
nodeSelector:
size: large$ kubectl create -f apple-pod.yaml
pod/apple-pod created
$ kubectl describe pod apple-pod
Name: apple-pod
Namespace: production
Priority: 0
Node: kubenode01/192.168.56.3
Start Time: Wed, 09 Dec 2020 12:10:34 +0000
Labels: app=apple
type=nginx-server
Annotations: <none>
Status: Running
IP: 10.44.0.2
IPs:
IP: 10.44.0.2
Containers:
nginx-container:
Container ID: docker://477b965d8dfa025ed881cb507ccc6fab3c95e139537ce44a3afabe25198e064f
Image: nginx
Image ID: docker-pullable://nginx@sha256:6b1daa9462046581ac15be20277a7c75476283f969cb3a61c8725ec38d3b01c3
Port: <none>
Host Port: <none>
State: Running
Started: Wed, 09 Dec 2020 12:10:39 +0000
Ready: True
Restart Count: 0
Environment: <none>
Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from default-token-9w5d7 (ro)
Conditions:
Type Status
Initialized True
Ready True
ContainersReady True
PodScheduled True
Volumes:
default-token-9w5d7:
Type: Secret (a volume populated by a Secret)
SecretName: default-token-9w5d7
Optional: false
QoS Class: BestEffort
Node-Selectors: size=large
Tolerations: node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 2m16s default-scheduler Successfully assigned production/apple-pod to kubenode01
Normal Pulling 2m15s kubelet Pulling image "nginx"
Normal Pulled 2m11s kubelet Successfully pulled image "nginx" in 4.200628629s
Normal Created 2m11s kubelet Created container nginx-container
Normal Started 2m11s kubelet Started container nginx-containerNode: kubenode01/192.168.56.3
Node Affinity feature provides us with advanced capabilities to limit pod placement on specific nodes.
apiVersion: v1
kind: Pod
metadata:
name: with-node-affinity
spec:
affinity:
nodeAffinity:
requiredDuringSchedulingIgnoredDuringExecution:
nodeSelectorTerms:
- matchExpressions:
- key: kubernetes.io/e2e-az-name
operator: In
values:
- e2e-az1
- e2e-az2
preferredDuringSchedulingIgnoredDuringExecution:
- weight: 1
preference:
matchExpressions:
- key: another-node-label-key
operator: In
values:
- another-node-label-value
containers:
- name: with-node-affinity
image: k8s.gcr.io/pause:2.0- source: https://kubernetes.io/docs/concepts/scheduling-eviction/assign-pod-node/
The type of node affinity defines the behaviour of the scheduler with respect to node affinity and the stages in the lifecycle of the pod.
- requiredDuringSchedulingIgnoredDuringExecution
- preferredDuringSchedulingIgnoredDuringExecution
- requiredDuringSchedulingRequiredDuringExecution
| DuringScheduling | DuringExecution | |
| 1 | Required | Ignored |
| 2 | Preferred | Ignroed |
| 3 | Required | Required |
When the pods is scheduled, Required, Preferred, Required.
When the pods is executed, Ignored, Ignored, Required.