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 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 get daemonset -A
• kubectl rollout daemonset
• StatefulSet
• aws-node

See also

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