nodeSelector

nodeSelector is the simplest recommended form of node selection constraint. nodeSelector is a field of PodSpec. It specifies a map of key-value pairs. For the pod to be eligible to run on a node, the node must have each of the indicated key-value pairs as labels (it can have additional labels as well). The most common usage is one key-value pair.

Attach a label to the node

Run kubectl get nodes to get the names of your cluster’s nodes.

kubectl get nodes

Output will be like

NAME                                           STATUS    ROLES     AGE       VERSION
ip-192-168-15-64.us-west-2.compute.internal    Ready     <none>    8d        v1.12.7
ip-192-168-38-150.us-west-2.compute.internal   Ready     <none>    8d        v1.12.7
ip-192-168-86-147.us-west-2.compute.internal   Ready     <none>    7d23h     v1.12.7
ip-192-168-92-222.us-west-2.compute.internal   Ready     <none>    8d        v1.12.7

Pick out the one that you want to add a label to, and then run

kubectl label nodes <node-name> <label-key>=<label-value> 

to add a label to the node you’ve chosen.

For example, if my node name is ‘ip-192-168-15-64.us-west-2.compute.internal’ and my desired label is ‘disktype=ssd’, then I can run

kubectl label nodes ip-192-168-15-64.us-west-2.compute.internal disktype=ssd

You can verify that it worked by re-running kubectl get nodes –show-labels and checking that the node now has a label. You can also use kubectl describe node “nodename” to see the full list of labels of the given node.

kubectl get nodes --show-labels

Output will be like

NAME                                           STATUS    ROLES     AGE       VERSION   LABELS
ip-192-168-15-64.us-west-2.compute.internal    Ready     <none>    8d        v1.12.7   alpha.eksctl.io/cluster-name=eksworkshop-eksctl,alpha.eksctl.io/instance-id=i-064fdae0afd3cbe8b,alpha.eksctl.io/nodegroup-name=ng-cd62916d,beta.kubernetes.io/arch=amd64,beta.kubernetes.io/instance-type=m5.large,beta.kubernetes.io/os=linux,disktype=ssd,failure-domain.beta.kubernetes.io/region=us-west-2,failure-domain.beta.kubernetes.io/zone=us-west-2d,kubernetes.io/hostname=ip-192-168-15-64.us-west-2.compute.internal
ip-192-168-38-150.us-west-2.compute.internal   Ready     <none>    8d        v1.12.7   alpha.eksctl.io/cluster-name=eksworkshop-eksctl,alpha.eksctl.io/instance-id=i-0420598c17da0a4b4,alpha.eksctl.io/nodegroup-name=ng-cd62916d,beta.kubernetes.io/arch=amd64,beta.kubernetes.io/instance-type=m5.large,beta.kubernetes.io/os=linux,failure-domain.beta.kubernetes.io/region=us-west-2,failure-domain.beta.kubernetes.io/zone=us-west-2c,kubernetes.io/hostname=ip-192-168-38-150.us-west-2.compute.internal
ip-192-168-86-147.us-west-2.compute.internal   Ready     <none>    7d23h     v1.12.7   alpha.eksctl.io/cluster-name=eksworkshop-eksctl,alpha.eksctl.io/instance-id=i-02e33f4429c64e628,alpha.eksctl.io/nodegroup-name=ng-cd62916d,beta.kubernetes.io/arch=amd64,beta.kubernetes.io/instance-type=m5.large,beta.kubernetes.io/os=linux,failure-domain.beta.kubernetes.io/region=us-west-2,failure-domain.beta.kubernetes.io/zone=us-west-2b,kubernetes.io/hostname=ip-192-168-86-147.us-west-2.compute.internal
ip-192-168-92-222.us-west-2.compute.internal   Ready     <none>    8d        v1.12.7   alpha.eksctl.io/cluster-name=eksworkshop-eksctl,alpha.eksctl.io/instance-id=i-02eadff5d2af1ce12,alpha.eksctl.io/nodegroup-name=ng-cd62916d,beta.kubernetes.io/arch=amd64,beta.kubernetes.io/instance-type=m5.large,beta.kubernetes.io/os=linux,failure-domain.beta.kubernetes.io/region=us-west-2,failure-domain.beta.kubernetes.io/zone=us-west-2b,kubernetes.io/hostname=ip-192-168-92-222.us-west-2.compute.internal

Add a nodeSelector field to your pod configuration

Take whatever pod config file you want to run, and add a nodeSelector section to it, like this. For example, if this is my pod config:

apiVersion: v1
kind: Pod
metadata:
  name: nginx
  labels:
    env: test
spec:
  containers:
  - name: nginx
    image: nginx

Then add a nodeSelector like so:

cat <<EoF > ~/environment/pod-nginx.yaml
apiVersion: v1
kind: Pod
metadata:
  name: nginx
  labels:
    env: test
spec:
  containers:
  - name: nginx
    image: nginx
    imagePullPolicy: IfNotPresent
  nodeSelector:
    disktype: ssd
EoF

Then you run

kubectl apply -f ~/environment/pod-nginx.yaml

And the Pod will get scheduled on the node that you attached the label to. You can verify that it worked by running

kubectl get pods -o wide

And looking at the “NODE” that the Pod was assigned to

NAME      READY     STATUS    RESTARTS   AGE       IP              NODE                                          NOMINATED NODE
nginx     1/1       Running   0          12s       192.168.10.13   ip-192-168-15-64.us-west-2.compute.internal   <none>