#DaemonSets

#Understanding DaemonSets

Refer to the official Kubernetes documentation: DaemonSets

A DaemonSet is a Kubernetes controller that ensures all (or a subset of) cluster nodes run exactly one replica of a specified Pod. Unlike Deployments, DaemonSets are node-centric rather than application-centric, making them ideal for deploying cluster-wide infrastructure services such as log collectors, monitoring agents, or storage daemons.

#Creating DaemonSets

#Creating a DaemonSet by using CLI

#Prerequisites

• Ensure you have kubectl configured and connected to your cluster.

#YAML file example

# example-daemonSet.yaml
apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: fluentd-elasticsearch
  namespace: kube-system
  labels:
    k8s-app: fluentd-logging
spec:
  selector: # defines how the DaemonSet identifies its managed Pods. Must match `template.metadata.label`s.
    matchLabels:
      name: fluentd-elasticsearch
  updateStrategy:
    type: RollingUpdate
    rollingUpdate:
      maxUnavailable: 1 
  template: # defines the Pod Template for the DaemonSet. Each Pod created by this DaemonSet will conform to this template
    metadata:
      labels:
        name: fluentd-elasticsearch
    spec:
      tolerations: # these tolerations are to have the daemonset runnable on control plane nodes, remove them if your control plane nodes should not run pods
      - key: node-role.kubernetes.io/control-plane
        operator: Exists
        effect: NoSchedule
      - key: node-role.kubernetes.io/master
        operator: Exists
        effect: NoSchedule
      containers:
      - name: fluentd-elasticsearch
        image: quay.io/fluentd_elasticsearch/fluentd:v2.5.2
        resources:
          limits:
            memory: 200Mi
          requests:
            cpu: 100m
            memory: 200Mi
        volumeMounts:
        - name: varlog
          mountPath: /var/log
      # it may be desirable to set a high priority class to ensure that a DaemonSet Pod
      # preempts running Pods
      # priorityClassName: important
      terminationGracePeriodSeconds: 30
      volumes:
      - name: varlog
        hostPath:
          path: /var/log

#Creating a DaemonSet via YAML

# Step 1: To create the DaemonSet defined in *example-daemonSet.yaml*, execute the following command
kubectl apply -f example-daemonSet.yaml

# Step 2: To verify the creation and status of your DaemonSet and its associated Pods:
kubectl get daemonset fluentd-elasticsearch # View DaemonSet
kubectl get pods -l name=fluentd-elasticsearch -o wide # Check Pods managed by this DaemonSet on specific nodes

#Creating a DaemonSet by using web console

#Prerequisites

Obtain the image address. The source of the images can be from the image repository integrated by the platform administrator through the toolchain or from third-party platforms' image repositories.

• For the former, the Administrator typically assigns the image repository to your project, and you can use the images within it. If the required image repository is not found, please contact the Administrator for allocation.

• If it is a third-party platform's image repository, ensure that images can be pulled directly from it in the current cluster.

#Procedure - Configure Basic Info

1. Container Platform, navigate to Workloads > DaemonSets in the left sidebar.

2. Click Create DaemonSet.

3. Select or Input an image, and click Confirm.

In the Basic Info section, configure declarative parameters for DaemonSet workloads:

#Procedure - Configure Pod

Pod section, please refer to Deployment - Configure Pod

#Procedure - Configure Containers

Containers section, please refer to Deployment - Configure Containers

#Procedure - Create

Click Create.

After clicking Create, the DaemonSet will:

• ✅ Automatically deploy Pod replicas to all eligible Nodes meeting:

  • nodeSelector criteria (if defined).
  • tolerations configuration (allowing scheduling on tainted nodes).
  • Node is in Ready state and Schedulable: true.

• ❌ Excluded Nodes:

  • Nodes with a NoSchedule taint (unless explicitly tolerated).
  • Manually cordoned Nodes (kubectl cordon).
  • Nodes in NotReady or Unschedulable states.

#Managing DaemonSets

#Managing a DaemonSet by using CLI

#Viewing a DaemonSet

• To get a summary of all DaemonSets in a namespace.

kubectl get daemonsets -n <namespace>

• To get detailed information about a specific DaemonSet, including its events and Pod status

kubectl describe daemonset <daemonset-name>

#Updating a DaemonSet

When you modify the Pod Template of a DaemonSet (e.g., changing the container image or adding a volume mount), Kubernetes automatically performs a rolling update by default (if updateStrategy.type is RollingUpdate, which is the default).

• First, edit the YAML file (e.g., example-daemonset.yaml) with the desired changes, then apply it:

kubectl apply -f example-daemonset.yaml

• You can monitor the progress of the rolling update:

kubectl rollout status daemonset/<daemonset-name>

#Deleting a DaemonSet

To delete a DaemonSet and all the Pods it manages:

kubectl delete daemonset <daemonset-name>

#Managing a DaemonSet by using web console

#Viewing a DaemonSet

1. Container Platform, and navigate to Workloads > DaemonSets.
2. Locate the DaemonSet you wish to view.
3. Click the DaemonSet name to see the Details, Topology, Logs, Events, Monitoring, etc.

#Updating a DaemonSet

1. Container Platform, and navigate to Workloads > DaemonSets.
2. Locate the DaemonSet you wish to update.
3. In the Actions drop-down menu, select Update to view the Edit DaemonSet page, you can update Replicas, image, updateStrategy, etc.

#Deleting a DaemonSet

1. Container Platform, and navigate to Workloads > DaemonSets.
2. Locate the DaemonSet you wish to delete.
3. In the Actions drop-down menu, Click the Delete button in the operations column and confirm.