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Kubernetes: 13. DaemonSets

Daemon Sets

  • DaemonSets are like replicaSet and deployment
  • While replicaSets and deployments makes sure that sufficient number of pods are running as defined in the replicas
  • DaemonSets make sure that atleast one pod runs on each node of the kubernetes cluster
  • If a new node is added to the cluster, DaemonSet automatically runs a pod on that node
  • Based on the node selector and node affinity rules, you can run DaemonSets only on targeted nodes
  • Some of the use cases of the DaemonSet are monitoring, log collector etc
  • Say you want to monitor pods running on the nodes, DaemonSet is perfect to make sure that monitoring agent is running via pod on every node
  • kube-proxy runs as a DaemonSet
  • DaemonSet definition file looks very similar to replicaSet definition
  • Before v1.12 kubernetes didnt had a way to create a pod on each node. The only way was to create a pod definition by setting the node name property
  • From v1.12 kubernetes now uses the combination of node affinity rules along with the daemon sets to schedule the pod on the node

daemon-set-definition.yaml
apiVersion: apps/v1
kind: DaemonSet
metadata:
    name: monitoring-daemon-agent

spec:
    selector:
        matchLabels:
            app: monitoring-pod-agent
    template:
        metadata:
            labels:
                app: monitoring-pod-agent
        spec:
            containers:
            - image: omi-agent
              name: omi-agent-container


kubectl create -f daemon-set-definition.yaml 
-> Create daemonset using the definition file

kubectl get daemonsets
-> View existing daemon sets

kubectl describle daemonset <daemon-set-name>
-> Get more information of the daemon-set deployed
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