What is a DaemonSet in Kubernetes and when would you use it?

A DaemonSet ensures that a copy of a pod runs on all (or specific) nodes in a Kubernetes cluster. When nodes are added to the cluster, the DaemonSet automatically schedules a pod on them.

How DaemonSets Work

Unlike Deployments which control a specific number of replicas, DaemonSets ensure one pod per matching node. When a node is removed, the pod is garbage collected.

Common Use Cases

• Log collection agents: Fluentd, Filebeat – collect logs from every node
• Monitoring agents: Prometheus Node Exporter, Datadog Agent – collect node metrics
• Network plugins: CNI plugins like Calico, Flannel run as DaemonSets
• Storage drivers: Ceph, GlusterFS storage daemons
• Security agents: Falco, Sysdig for runtime security monitoring

Example DaemonSet

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: node-exporter
  namespace: monitoring
spec:
  selector:
    matchLabels:
      app: node-exporter
  template:
    metadata:
      labels:
        app: node-exporter
    spec:
      tolerations:
      - key: node-role.kubernetes.io/master
        effect: NoSchedule
      containers:
      - name: node-exporter
        image: prom/node-exporter:latest
        ports:
        - containerPort: 9100

DaemonSet vs Deployment

Node Selection

Use nodeSelector or nodeAffinity to restrict a DaemonSet to specific nodes (e.g., only GPU nodes, only Linux nodes).