OpenShift Container Platform

Create daemonsets

Create a daemon set to automatically deploy and maintain pod replicas across selected nodes in your cluster, using node selectors to control placement.

When creating daemon sets, the nodeSelector field is used to indicate the nodes on which the daemon set should deploy replicas.

If you update a daemon set pod template, the existing pod replicas are not affected.
If you delete a daemon set and then create a new daemon set with a different template but the same label selector, it recognizes any existing pod replicas as having matching labels. It does not update them or create new replicas despite a mismatch in the pod template.
If you change node labels, the daemon set adds pods to nodes that match the new labels and deletes pods from nodes that do not match the new labels.

To update a daemon set, force new pod replicas to be created by deleting the old replicas or nodes.

Prerequisites

The default project-wide node selector in your namespace is set to an empty string by using the openshift.io/node-selector annotation:

$ oc patch namespace myproject -p \
    '{"metadata": {"annotations": {"openshift.io/node-selector": ""}}}'

You can alternatively apply the following YAML to disable the default project-wide node selector for a namespace:

apiVersion: v1
kind: Namespace
metadata:
  name: <namespace>
  annotations:
    openshift.io/node-selector: ''
#...

If you are creating a new project, the default node selector is overwritten:
```
$ oc adm new-project <name> --node-selector=""
```

Procedure

Define the daemon set yaml file:

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: hello-daemonset
spec:
  selector:
      matchLabels:
        name: hello-daemonset
  template:
    metadata:
      labels:
        name: hello-daemonset
    spec:
      nodeSelector:
        role: worker
      containers:
      - image: openshift/hello-openshift
        imagePullPolicy: Always
        name: registry
        ports:
        - containerPort: 80
          protocol: TCP
        resources: {}
        terminationMessagePath: /dev/termination-log
      serviceAccount: default
      terminationGracePeriodSeconds: 10
#...

where:

spec.selector.matchLabels.name: Specifies the label selector that determines which pods belong to the daemon set.
spec.template.metadata.labels.name: Specifies the pod template’s label selector. Must match the label selector above.
spec.template.spec.nodeSelector: Specifies the node selector that determines on which nodes pod replicas should be deployed. A matching label must be present on the node.

Create the daemon set object by running the following command:
```
$ oc create -f daemonset.yaml
```

Verification

Verify that the pods were created and that each node has a pod replica by running the following command:

$ oc get pods

Example output

hello-daemonset-cx6md   1/1       Running   0          2m
hello-daemonset-e3md9   1/1       Running   0          2m

Verify that the pods are placed onto the correct nodes by running the following command:

$ oc describe pod/hello-daemonset-cx6md|grep Node

Example output

Node:        openshift-node01.hostname.com/10.14.20.134