DaemonSets in Kubernetes

A DaemonSets are like ReplicaSets, as it helps you deploy multiple instances of the pod, but it runs one pod on each node in the cluster. Whenever a new node is added to the cluster, a DaemonSet pod is automatically added to that node, and when a node is removed DaemonSet pod automatically removed. A DaemonSet ensures that all (or some) Nodes run a copy of a Pod. As nodes are added to the cluster, Pods are added to them. As nodes are removed from the cluster, those Pods are garbage collected. Deleting a DaemonSet will clean up the Pods it created.

Some 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

In the Kubernetes architecture, Kube-proxy is required on every node in the cluster. That is one good use case of demonSets. The Kube-proxy component can be deployed as a daemonSet in the cluster.

DaemonSet Definition

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: nginx-daemonset
  labels:
    app: nginx
spec:
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      name: nginx-pod
      labels:
        app: nginx
    spec:
      containers:
        - name: nginx-container
          image: nginx
          ports:
            - containerPort: 80
              protocol: TCP

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

$ kubectl create -f nginx-daemonsets.yaml 
daemonset.apps/nginx-daemonset created

$ kubectl get daemonset
NAME              DESIRED   CURRENT   READY   UP-TO-DATE   AVAILABLE   NODE SELECTOR   AGE
nginx-daemonset   1         1         1       1            1           <none>          15s

$ kubectl get pods
NAME                    READY   STATUS    RESTARTS   AGE
nginx-daemonset-ml7rk   1/1     Running   0          33s

• Minikube has one node thus, the pod is only one.