Using Daemonsets
Overview
A daemonset can be used to run replicas of a pod on specific or all nodes in an OKD cluster.
Use daemonsets to create shared storage, run a logging pod on every node in your cluster, or deploy a monitoring agent on every node.
For security reasons, only cluster administrators can create daemonsets. (Granting Users Daemonset Permissions.)
For more information on daemonsets, see the Kubernetes documentation.
Daemonset scheduling is incompatible with project’s default node selector. If you fail to disable it, the daemonset gets restricted by merging with the default node selector. This results in frequent pod recreates on the nodes that got unselected by the merged node selector, which in turn puts unwanted load on the cluster. Therefore,
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Creating Daemonsets
When creating daemonsets, the **nodeSelector**
field is used to indicate the nodes on which the daemonset should deploy replicas.
Define the daemonset yaml file:
apiVersion: extensions/v1beta1
kind: DaemonSet
metadata:
name: hello-daemonset
spec:
selector:
matchLabels:
name: hello-daemonset (1)
template:
metadata:
labels:
name: hello-daemonset (2)
spec:
nodeSelector: (3)
type: infra
containers:
- image: openshift/hello-openshift
imagePullPolicy: Always
name: registry
ports:
- containerPort: 80
protocol: TCP
resources: {}
terminationMessagePath: /dev/termination-log
serviceAccount: default
terminationGracePeriodSeconds: 10
1 The label selector that determines which pods belong to the daemonset. 2 The pod template’s label selector. Must match the label selector above. 3 The node selector that determines on which nodes pod replicas should be deployed. Create the daemonset object:
oc create -f daemonset.yaml
To verify that the pods were created, and that each node has a pod replica:
Find the daemonset pods:
$ oc get pods
hello-daemonset-cx6md 1/1 Running 0 2m
hello-daemonset-e3md9 1/1 Running 0 2m
View the pods to verify the pod has been placed onto the node:
$ oc describe pod/hello-daemonset-cx6md|grep Node
Node: openshift-node01.hostname.com/10.14.20.134
$ oc describe pod/hello-daemonset-e3md9|grep Node
Node: openshift-node02.hostname.com/10.14.20.137
To update a DaemonSet, force new pod replicas to be created by deleting the old replicas or nodes. |