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Kubernetes DaemonSets

What are DaemonSets?​

DaemonSets are operators that manage node agents. They work like ReplicaSets/Deployments but with one key difference:

  • Enforces single Pod replica per Node
  • Similar to ReplicaSet/Deployment in other ways
  • Ensures a specific Pod type runs on all Nodes (or selected subset)

Key Characteristics​

  • One Pod per Node - Unlike ReplicaSet/Deployment which can place multiple Pods on same Node
  • Automatic placement - When a Node is added to cluster, DaemonSet Pod is automatically placed
  • Controller-managed - Pods are placed by controller, not the default Scheduler
  • Auto cleanup - When Node crashes or is removed, DaemonSet Pods are garbage collected

Common Use Cases​

  • Monitoring - Collecting monitoring data from all Nodes
  • Infrastructure daemons - Running storage, networking, or proxy daemons on all Nodes
  • Real examples: kube-proxy, Calico/Cilium networking agents

Scheduling Control​

You can limit Pod placement using:

  • nodeSelectors - Simple node selection
  • Node affinity rules - Advanced node selection
  • Taints and tolerations - Node exclusion/inclusion rules
  • Default Scheduler - Can enable it to take over if needed

Example YAML Structure​

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: fluentd-agent
  namespace: default
  labels:
    k8s-app: fluentd-agent
spec:
  selector:
    matchLabels:
      k8s-app: fluentd-agent
  template:
    metadata:
      labels:
        k8s-app: fluentd-agent
    spec:
      containers:
      - name: fluentd
        image: quay.io/fluentd_elasticsearch/fluentd:v4.5.2

Key Commands​

Create DaemonSet​

# Create from file
kubectl create -f fluentd-ds.yaml
kubectl apply -f fluentd-ds.yaml --record

View DaemonSets​

# Basic listing
kubectl get daemonsets
kubectl get ds -o wide

# Detailed info
kubectl get ds fluentd-agent -o yaml
kubectl get ds fluentd-agent -o json
kubectl describe ds fluentd-agent

# With labels
kubectl get all -l k8s-app=fluentd-agent -o wide
kubectl get ds,po -l k8s-app=fluentd-agent

Manage Updates​

# Check rollout status
kubectl rollout status ds fluentd-agent

# View history
kubectl rollout history ds fluentd-agent
kubectl rollout history ds fluentd-agent --revision=1

# Update image
kubectl set image ds fluentd-agent fluentd=new-image --record

# Rollback
kubectl rollout undo ds fluentd-agent --to-revision=1

Cleanup​

# Delete DaemonSet
kubectl delete ds fluentd-agent

Important Notes​

  • Critical for multi-node clusters - Essential component for distributed systems
  • Deletion impact - Deleting a DaemonSet removes all its Pod replicas
  • Scheduling rules apply - Pod placement still follows scheduling properties for Node selection