Working with DaemonSets

1. Creating DaemonSet

Field	Description	Example
apiVersion	API version to use	`apps/v1`
kind	Resource type	`DaemonSet`
metadata.name	Name of the DaemonSet	`fluentd-elasticsearch`
spec.selector	Label selector for pods	`{"matchLabels": {"name": "fluentd-elasticsearch"}}`
spec.template	Pod template to be used	`{"metadata": {"labels": {"name": "fluentd-elasticsearch"}}, "spec": {"containers": [...]}}`

Example: Basic DaemonSet YAML

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: fluentd-elasticsearch
spec:
  selector:
    matchLabels:
      name: fluentd-elasticsearch
  template:
    metadata:
      labels:
        name: fluentd-elasticsearch
    spec:
      containers:
      - name: fluentd-elasticsearch
        image: quay.io/fluent/fluentd-kubernetes-daemonset:v1.15.0
        resources:
          limits:
            memory: 200Mi
          requests:
            cpu: 100m
            memory: 200Mi

2. Listing DaemonSets

Command	Description	Notes
kubectl get daemonsets	List all DaemonSets in the current namespace	Alias: `kubectl get ds`
kubectl get daemonsets -A	List all DaemonSets across all namespaces	Useful for cluster-wide overview
kubectl get daemonsets -n <namespace>	List DaemonSets in a specific namespace	Replace <namespace> with actual namespace name
kubectl get daemonsets -o wide	Get detailed information including node names	Shows which nodes each DaemonSet is scheduled on

Example: Listing DaemonSets in the default namespace

kubectl get daemonsets

Example: Listing all DaemonSets across all namespaces

kubectl get daemonsets -A

3. Describing DaemonSet Details

Property	Description	Example Value
apiVersion	The API version for the DaemonSet resource	`apps/v1`
kind	Resource type — must be `DaemonSet`	`DaemonSet`
metadata.name	Unique name for the DaemonSet within the namespace	`fluentd-elasticsearch`
metadata.namespace	Namespace where the DaemonSet is deployed	`default`
spec.selector	Label selector used to identify pods managed by this DaemonSet	`{"matchLabels": {"name": "fluentd-elasticsearch"}}`
spec.template	Pod template used to create pods on each node	`{ "metadata": { "labels": {"name": "fluentd-elasticsearch"} }, "spec": { "containers": [ { "name": "fluentd", "image": "fluent/fluentd-kubernetes-daemonset:v2.5.2" } ] } }`
spec.updateStrategy	Strategy to use when updating pods (e.g., `RollingUpdate`)	`{"type": "RollingUpdate", "rollingUpdate": {"maxUnavailable": 1}}`
spec.minReadySeconds	Minimum number of seconds a new pod must be ready before it's considered available	`30`
spec.revisionHistoryLimit	Number of revisions to keep for rollback purposes	`10`

Example: DaemonSet YAML Definition

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: fluentd-elasticsearch
  namespace: default
spec:
  selector:
    matchLabels:
      name: fluentd-elasticsearch
  template:
    metadata:
      labels:
        name: fluentd-elasticsearch
    spec:
      containers:
      - name: fluentd
        image: fluent/fluentd-kubernetes-daemonset:v2.5.2
      tolerations:
      - key: node-role.kubernetes.io/master
        effect: NoSchedule
  updateStrategy:
    type: RollingUpdate
    rollingUpdate:
      maxUnavailable: 1
  minReadySeconds: 30

Note: The spec.template field defines the pod template that will be used to create pods on each node. It must include a valid metadata and spec.

Warning: DaemonSets do not support replicas, as they ensure one pod per node matching the selector.

4. Understanding DaemonSet Scheduling

Field	Description	Values
spec.selector	Selector used to identify pods managed by the DaemonSet	`{matchLabels: {name: "daemon-pod"}}`
spec.template	Template for creating pods	PodSpec object
spec.updateStrategy	How to update pods when the DaemonSet is updated	`RollingUpdate` or `OnDelete`

Example: DaemonSet with update strategy

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: fluentd-elasticsearch
spec:
  selector:
    matchLabels:
      name: fluentd-elasticsearch
  template:
    metadata:
      labels:
        name: fluentd-elasticsearch
    spec:
      containers:
      - name: fluentd-elasticsearch
        image: quay.io/fluentd_elasticsearch/fluentd:v2.5.2
  updateStrategy:
    type: RollingUpdate

Note: DaemonSets ensure one pod per node matching the selector. The update strategy determines how existing pods are replaced during updates.

5. Using Node Selectors

Field	Description	Example
nodeSelector	Map of key-value pairs for node labels to match	`{"node-type": "production"}`
nodeAffinity	More flexible way to select nodes using operators like In, NotIn, Exists	`{ "requiredDuringSchedulingIgnoredDuringExecution": { "nodeSelectorTerms": [ { "matchExpressions": [ { "key": "environment", "operator": "In", "values": ["production"] } ] } ] } }`

Example: DaemonSet with Node Selector

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: fluentd-elasticsearch
spec:
  selector:
    matchLabels:
      app: fluentd-elasticsearch
  template:
    metadata:
      labels:
        app: fluentd-elasticsearch
    spec:
      nodeSelector:
        node-type: production
      containers:
      - name: fluentd-elasticsearch
        image: quay.io/fluentd_elasticsearch/fluentd:v2.5.2

Note: nodeSelector is a simple label match. For more complex logic, use nodeAffinity.

6. Using Node Affinity

Field	Description	Values
nodeSelector	Simple label-based node selection	`{"key": "value"}`
affinity.nodeAffinity	Advanced node affinity rules	`{"requiredDuringSchedulingIgnoredDuringExecution": {...}, "preferredDuringSchedulingIgnoredDuringExecution": [...]}`

Example: Node Affinity Configuration

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: example-daemonset
spec:
  selector:
    matchLabels:
      app: example
  template:
    metadata:
      labels:
        app: example
    spec:
      affinity:
        nodeAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
            nodeSelectorTerms:
              - matchExpressions:
                  - key: kubernetes.io/e2e-az-name
                    operator: In
                    values:
                      - e2e-az1
                      - e2e-az2
          preferredDuringSchedulingIgnoredDuringExecution:
            - weight: 1
              preference:
                matchExpressions:
                  - key: another-node-label-key
                    operator: In
                    values:
                      - another-node-label-value
      containers:
        - name: example-container
          image: nginx:latest

Note: requiredDuringSchedulingIgnoredDuringExecution is a hard requirement, while preferredDuringSchedulingIgnoredDuringExecution is a soft preference.

7. Tolerating Taints

Field	Description	Example
tolerations	List of tolerations to apply to the DaemonSet	`[ { "key": "node-role.kubernetes.io/master", "effect": "NoSchedule" } ]`

Example: Tolerating Master Node Taints

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: example-daemonset
spec:
  selector:
    matchLabels:
      app: example
  template:
    metadata:
      labels:
        app: example
    spec:
      tolerations:
      - key: "node-role.kubernetes.io/master"
        effect: "NoSchedule"
        operator: "Exists"
      containers:
      - name: example-container
        image: nginx

Note: Tolerations allow pods to be scheduled on nodes with matching taints. The operator: "Exists" means any taint with the specified key will be tolerated.

8. Updating DaemonSets

Field	Description	Values
spec.updateStrategy.type	Update strategy type for the DaemonSet	`RollingUpdate`, `OnDelete`
spec.updateStrategy.rollingUpdate.maxUnavailable	Maximum number of DaemonSet pods that can be unavailable during the update	`1`, `2`, `50%`

Example: Update DaemonSet with RollingUpdate

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: example-daemonset
spec:
  updateStrategy:
    type: RollingUpdate
    rollingUpdate:
      maxUnavailable: 1
  selector:
    matchLabels:
      app: example-app
  template:
    metadata:
      labels:
        app: example-app
    spec:
      containers:
      - name: example-container
        image: nginx:latest

9. Setting Max Unavailable

Field	Description	Default Value	Notes
maxUnavailable	Maximum number of DaemonSet pods that can be unavailable during an update	1	Can be specified as a number or percentage (e.g., 1, 20%)

Example: Setting maxUnavailable to 20%

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: example-daemonset
spec:
  selector:
    matchLabels:
      app: example-app
  template:
    metadata:
      labels:
        app: example-app
    spec:
      containers:
      - name: example-container
        image: nginx:latest
  updateStrategy:
    rollingUpdate:
      maxUnavailable: 20%

Note: When maxUnavailable is set to a percentage, it is calculated based on the total number of nodes running the DaemonSet.

10. Deleting DaemonSets

Field	Description	Values
metadata.name	Name of the DaemonSet	`example-daemonset`
metadata.namespace	Namespace where the DaemonSet is located	`default`

Example: Delete a DaemonSet

kubectl delete daemonset example-daemonset -n default

Note: Deleting a DaemonSet will remove all pods managed by it.

Warning: Ensure that deleting the DaemonSet won't impact critical services or nodes.

11. Troubleshooting DaemonSet Pods

Issue	Possible Cause	Solution
Pods stuck in Pending	Node resource constraints (CPU/Memory)	Check node resources with `kubectl describe node <node-name>`
Pods stuck in ContainerCreating	Image pull issues or invalid container config	Run `kubectl describe pod <pod-name>` to see events
Pods CrashLoopBackOff	Application errors or misconfiguration	Check logs with `kubectl logs <pod-name>`
Pods Not Scheduled	NodeSelector or Taints/Tolerations mismatch	Verify node labels and tolerations match DaemonSet spec

Example: Check DaemonSet Pod Status

kubectl get pods -l app=nginx-daemonset -o wide
kubectl describe pod <pod-name>

Note: Use kubectl get pods --all-namespaces to check all DaemonSet pods across namespaces.

Warning: Avoid modifying DaemonSet pods directly; changes are overwritten by the controller.