What is the practical use of DaemonSet in Kubernetes?

A DaemonSet ensures that a copy of a Pod is always running on each node of a Kubernetes cluster or on a subset of nodes matching specified criteria. This is useful for deploying:

1. Log collectors: Agents like Fluentd or Logstash for collecting logs from each node.
2. Monitoring agents: Metric exporters such as Node Exporter for Prometheus, for collecting metrics from nodes.
3. System daemons: For example, kube-proxy to provide network functions on each node or storage agents.

Advantages of DaemonSet:

• Automatic deployment of Pods on new nodes.
• Automatic removal of Pods when a node is deleted.
• Guarantee of an instance on each target node.

Example of a DaemonSet definition:

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: fluentd-logging
  labels:
    app: fluentd-logging
spec:
  selector:
    matchLabels:
      name: fluentd-logging
  template:
    metadata:
      labels:
        name: fluentd-logging
    spec:
      containers:
      - name: fluentd
        image: fluentd:latest
        # ... other container settings