Kubernetes DaemonSets

Kubernetes Daemonset can be used to run replicas of a pod on specific or all nodes.

• https://kubernetes.io/docs/concepts/workloads/controllers/daemonset/
• https://kubernetes.io/docs/concepts/workloads/controllers/replicaset/#daemonset

Typical uses of a DaemonSet are:

• Running a cluster storage daemon on every node
• Running a logs collection daemon on every node
• Running a node monitoring daemon on every node

Official example

https://kubernetes.io/docs/concepts/workloads/controllers/daemonset/

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: fluentd-elasticsearch
  namespace: kube-system 
  labels:
    k8s-app: fluentd-logging
spec:
  selector: 
    matchLabels:
      name: fluentd-elasticsearch
  template:
    metadata:
      labels:
        name: fluentd-elasticsearch
    spec:
      tolerations:
     # these tolerations are to have the daemonset runnable on control plane node
     # remove them if your control plane nodes should not run pods
     - key: node-role.kubernetes.io/control-plane

        operator: Exists

        effect: NoSchedule

      - key: node-role.kubernetes.io/master

        operator: Exists

        effect: NoSchedule

      containers:

      - name: fluentd-elasticsearch

        image: quay.io/fluentd_elasticsearch/fluentd:v2.5.2

        resources:

          limits:

            memory: 200Mi

          requests:

            cpu: 100m

            memory: 200Mi

        volumeMounts:

        - name: varlog

          mountPath: /var/log

        - name: varlibdockercontainers

          mountPath: /var/lib/docker/containers

          readOnly: true

      terminationGracePeriodSeconds: 30

      volumes:

      - name: varlog

        hostPath:

          path: /var/log

      - name: varlibdockercontainers

        hostPath:

          path: /var/lib/docker/containers

Activities

• CKA v1.18: Understand the role of DaemonSets
• Stop daemonset: kubectl -n <namespace> patch daemonset <name-of-daemon-set> -p '{"spec": {"template": {"spec": {"nodeSelector": {"non-existing": "true"}}}}}'

Related terms

• kubectl api-resources
• kind: DaemonSet
• kubectl get daemonset
• kubectl rollout daemonset
• StatefulSet

See also

• DaemonSet, kind: DaemonSet, tolerations:
• Kubernetes Workloads: Deployment, ReplicaSet, StatefulSet, DaemonSets, Job, CronJob, .apps/