↓Skip to main content

Kubernetes Sets - ReplicaSets & DaemonSets: Overview, Example ReplicaSet, Example DaemonSet with and without NodeSelector / Node Labeling

1365 words·
Kubernetes Kubectl ReplicaSets DaemonSets NodeSelector
Table of Contents
Kubernetes-Components - This article is part of a series.
Part 1: Kubernetes Configuration Manifests: Create Manifests from RAW Output and Dry-Run Command
Part 2: Kubernetes Non-Disruptive & Disruptive Configuration Updates: Kubectl Apply, Edit, Patch & Replace; Update Rollouts and Rollbacks with Set Image Command
Part 3: Kubernetes Pods: Create Pods with Run-Command and YAML Configuration; Single & Multi Container Pods, Port-Forwarding, Find Container on Worker Node
Part 4: Kubernetes Pods: Init & Sidecar Container Overview, Init Container Examples
Part 5: Kubernetes Kubernetes Deployments & Replication Controllers (Soon Depricated): Example Deployment with Create-Command and YAML Configuration, Scale the Deployment; Example Replication Controller
Part 6: Kubernetes Services: Example ClusterIP, NodePort & LoadBalancer Services with Expose-Command and YAML Configuration; Service for External Endpoint
Part 7: Kubernetes Resource Management: Deploy Kubernetes Metrics Server, Vish/Stress Container Example, Define Resource Requests and Limits, Verify Resource Usage with kubectl top, Define a LimitRange for a Namespace
Part 8: Kubernetes Monitoring & Logs: Monitor Applications with top, Monitor Events Pod specific and Cluster wide, Container STDOUT and STDERR Logs
Part 9: Kubernetes Security: Immutable Deployment - Deploy Container with ReadOnly-Filesystem and Writable-Volume
Part 10: Kubernetes Security: Pod Security Admission (PSA) - Overview, Enforce Pod Security Standard at a Namespace; Example Nginx Pod SecurityContext for Restricted PSS
Part 11: Kubernetes Volumes: Nginx Pod and Deployment Examples with NFS Volume, Pod and Deployment Examples with EmptyDir Volume, Deployment Example with PersistentVolume, External Storage Provider with NFS
Part 12: Kubernetes Secrets: Opaque Secret Configuration, Pod Examples with Environment Variable Secrets and Volume Secrets; SSH Authentication Secret with Pod Example
Part 13: Kubernetes ConfigMaps: Mount ConfigMap to Pod as Volume, Mount ConfigMap as Environment Variable
Part 14: This Article
Part 15: Kubernetes Sets - StatefulSets: Difference between StatefulSet & ReplcaSet; StatefulSet Example with VolumeClaimTemplate and Stateless Service
Part 16: Kubernetes Labels, Annotations, Affinity / Anti-Affinity, Taints & Tolerations: Node Labeling, Pod Labeling & NodeSelector; Pod Annotations; Node Affinity, Pod Anti-Affinity; Node Taints and Pod Tolerations
Part 17: Kubernetes Configuration Management - Helm Charts: Create a Custom Helm Chart
Part 18: Kubernetes Configuration Management - Kustomize: Kustomize Example
Part 19: Kubernetes Networking - Network Policies: Ingress and Egress Policy Examples
Part 20: Kubernetes Networking - Liveness, Readiness & Startup Probe Examples: Liveness Probe (TCP), Readiness Probes (TCP / Single Pod and Multi Pod Dependency), Startup Probe (Command, TCP & HTTP)
Part 21: Kubernetes Networking - DNS: CoreDNS custom Hosts entry (K3s & K8s Version), Deployment with custom Hosts entry; Backup and Restore the CoreDNS ConfigMap; DNS Troubleshooting
Part 22: Kubernetes Horizontal Pod Autoscaling: Install Kubernetes Metrics Server, Example Deployment with Horizontal Pod Autoscaler (HPA)
Part 23: Kubernetes Jobs: Jobs Overview, Basic Non-parallel & Parallel Job Examples; CronJob & RBAC Example that Restarts a Deployment
Part 24: Kubernetes Role Based Access Control (RBAC): RBAC Overview, Create Service Account, Example Role and RoleBinding
Part 25: Kubernetes Kubeconfig: Create example Kubeconfig with new (RBAC) Service Account and ClusterRole / ClusterRole Binding
Part 26: Kubernetes Etcd Snapshot: Etcd Snapshot and Restore with Etcdctl, Verify Etcd Member Health; Etcdctl Commands
Part 27: Kubernetes Troubleshooting: Cluster, Nodes, Pods & Kubelet
Part 28: Kubernetes Commands: Kubectl Autocomplete, Cluster Nodes, Namespaces, LimitRange Resource Limits, Pods, Deployments, Replication Controllers, Services, HPA, Secrets, Cronjobs, Helm, Logs, K9s TUI

Overview
#

In this tutorial I’m using the following K3s cluster with 3 worker nodes:

NAME      STATUS   ROLES                  AGE   VERSION        INTERNAL-IP     EXTERNAL-IP   OS-IMAGE             KERNEL-VERSION     CONTAINER-RUNTIME
ubuntu1   Ready    control-plane,master   10d   v1.30.5+k3s1   192.168.30.10   <none>        Ubuntu 24.04.1 LTS   6.8.0-45-generic   containerd://1.7.21-k3s2
ubuntu2   Ready    worker                 10d   v1.30.5+k3s1   192.168.30.11   <none>        Ubuntu 24.04.1 LTS   6.8.0-45-generic   containerd://1.7.21-k3s2
ubuntu3   Ready    worker                 10d   v1.30.5+k3s1   192.168.30.12   <none>        Ubuntu 24.04.1 LTS   6.8.0-45-generic   containerd://1.7.21-k3s2
ubuntu4   Ready    worker                 10d   v1.30.5+k3s1   192.168.30.13   <none>        Ubuntu 24.04.1 LTS   6.8.0-45-generic   containerd://1.7.21-k3s2

Prerequisites
#

Create Namespace
# 

# Create a "example-deployment" namespace for the example deployment
kubectl create ns example-deployment

ReplicaSets
#

ReplicaSet Overview
#

  • Ensures a specified number of pod replicas are running at all times. The placement of those pods across nodes is handled by Kubernetes.

  • Pods are scheduled regarding available resources on the Kubernetes nodes. It does not matter if the pods are distributed on all nodes. Only that the right number of pods running across the cluster counts.

  • Failed pods are terminated and it will start another pod to maintain the defined number of running pods.

Note: The “restartPolicy” in a pod only affects how the individual containers in the pod behave when they exit or fail, not the behavior of the ReplicaSet itself.


Example ReplicaSet (Without Node Selection)
#

Example Deployment
# 

# Create a manifest for the deployment
vi example-deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: example-deployment
  namespace: example-deployment
  labels:
    app: some-pod
spec:
  replicas: 3
  selector:
    matchLabels:
      app: some-pod
  template:
    metadata:
      labels:
        app: some-pod
    spec:
      containers:
        - name: busybox
          image: busybox:latest
          command: ['sh', '-c', 'tail -f /dev/null']
          imagePullPolicy: IfNotPresent
      restartPolicy: Always

# Apply the manifest
kubectl apply -f example-deployment.yaml

Verify Deployment
#

Verify the ReplicaSet:

# List the ReplicaSets in the "example-deployment" namespace
kubectl get replicaset -n example-deployment

# Shell output:
NAME                            DESIRED   CURRENT   READY   AGE
example-deployment-7fcf97b89d   3         3         3       7s

Verify the Pods:

# List pods in the "example-deployment" namespace
kubectl get pods -o wide -n example-deployment

# Shell output:
NAME                                  READY   STATUS    RESTARTS   AGE   IP           NODE      NOMINATED NODE   READINESS GATES
example-deployment-7fcf97b89d-bph8k   1/1     Running   0          77s   10.42.3.30   ubuntu4   <none>           <none>
example-deployment-7fcf97b89d-fsl72   1/1     Running   0          77s   10.42.2.29   ubuntu3   <none>           <none>
example-deployment-7fcf97b89d-t978k   1/1     Running   0          77s   10.42.1.28   ubuntu2   <none>           <none>

Verify all Resources:

# List resources in the "example-deployment" namespace
kubectl get all -n example-deployment

# Shell output:
NAME                                      READY   STATUS    RESTARTS   AGE
pod/example-deployment-7fcf97b89d-bph8k   1/1     Running   0          2m3s
pod/example-deployment-7fcf97b89d-fsl72   1/1     Running   0          2m3s
pod/example-deployment-7fcf97b89d-t978k   1/1     Running   0          2m3s

NAME                                 READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/example-deployment   3/3     3            3           2m3s

NAME                                            DESIRED   CURRENT   READY   AGE
replicaset.apps/example-deployment-7fcf97b89d   3         3         3       2m3s

Delete the Deployment
# 

# Delete the deployment
kubectl delete deployment example-deployment -n example-deployment



Example ReplicaSet (With Node Selection)
#

Label Kubernetes Nodes
# 

# List Kubernetes nodes
kubectl get nodes -o wide

# Shell output:
NAME      STATUS   ROLES                  AGE   VERSION        INTERNAL-IP     EXTERNAL-IP   OS-IMAGE             KERNEL-VERSION     CONTAINER-RUNTIME
ubuntu1   Ready    control-plane,master   10d   v1.30.5+k3s1   192.168.30.10   <none>        Ubuntu 24.04.1 LTS   6.8.0-45-generic   containerd://1.7.21-k3s2
ubuntu2   Ready    worker                 10d   v1.30.5+k3s1   192.168.30.11   <none>        Ubuntu 24.04.1 LTS   6.8.0-45-generic   containerd://1.7.21-k3s2
ubuntu3   Ready    worker                 10d   v1.30.5+k3s1   192.168.30.12   <none>        Ubuntu 24.04.1 LTS   6.8.0-45-generic   containerd://1.7.21-k3s2
ubuntu4   Ready    worker                 10d   v1.30.5+k3s1   192.168.30.13   <none>        Ubuntu 24.04.1 LTS   6.8.0-45-generic   containerd://1.7.21-k3s2

# Label one or more of the Kubernetes nodes
kubectl label node ubuntu2 project=app-no-1

Verify Node Labels
# 

# List "monitoring-enabled" label
kubectl get nodes -o custom-columns=NAME:.metadata.name,project:.metadata.labels.project

# Shell output:
NAME      project
ubuntu1   <none>
ubuntu2   app-no-1
ubuntu3   <none>
ubuntu4   <none

Example Deployment
# 

# Create a manifest for the deployment
vi example-deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: example-deployment
  namespace: example-deployment
  labels:
    app: some-pod
spec:
  replicas: 4
  selector:
    matchLabels:
      app: some-pod
  template:
    metadata:
      labels:
        app: some-pod
    spec:
      nodeSelector:
        project: "app-no-1"
      containers:
        - name: busybox
          image: busybox:latest
          command: ['sh', '-c', 'tail -f /dev/null']
          imagePullPolicy: IfNotPresent
      restartPolicy: Always

# Apply the manifest
kubectl apply -f example-deployment.yaml

Verify Deployment
# 

# List pods in "example-deployment" namespace
kubectl get pods -o wide -n example-deployment

# Shell output:
NAME                                 READY   STATUS    RESTARTS   AGE   IP          NODE      NOMINATED NODE   READINESS GATES
example-deployment-f98f569bc-hdxvd   1/1     Running   0          20s   10.42.1.7   ubuntu2   <none>           <none>
example-deployment-f98f569bc-ktms9   1/1     Running   0          20s   10.42.1.4   ubuntu2   <none>           <none>
example-deployment-f98f569bc-kv4x5   1/1     Running   0          20s   10.42.1.6   ubuntu2   <none>           <none>
example-deployment-f98f569bc-vb65n   1/1     Running   0          20s   10.42.1.5   ubuntu2   <none>           <none>

Delete the Deployment
# 

# Delete the deployment
kubectl delete deployment example-deployment -n example-deployment



DaemonSets
#

DaemonSet Overview
#

  • Ensures that a copy of a pod runs on every Kubernetes node.

  • New Kubernetes nodes that join the cluster will automatically start pods that are part of a DaemonSet.

  • Kubernetes will deschedule pods of a DaemonSet when nodes are deprovisioned.

  • DaemonSets are designed to run a Pod on every Node, also in situations that would normally be prevented. DaemonSet pods will still be scheduled even if a target Node is facing resource constraints or isn’t accepting new Pods.

  • DaemonSets are often used for node monitoring and log collection agents.


Example DaemonSet (All Nodes)
#

Example Deployment
# 

# Create a manifest for the deployment
vi example-daemonset.yaml

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: example-daemonset
  namespace: example-deployment
spec:
  selector:
    matchLabels:
      app: some-pod
  template:
    metadata:
      labels:
        app: some-pod
    spec:
      containers:
        - name: busybox
          image: busybox:latest
          command: ['sh', '-c', 'tail -f /dev/null']
          imagePullPolicy: IfNotPresent
      restartPolicy: Always

# Apply the manifest
kubectl apply -f example-daemonset.yaml

Verify Deployment
#

Verify the ReplicaSet:

# List the DaemonSet in the "example-deployment" namespace
kubectl get daemonset -n example-deployment

# Shell output:
NAME                DESIRED   CURRENT   READY   UP-TO-DATE   AVAILABLE   NODE SELECTOR   AGE
example-daemonset   4         4         4       4            4           <none>          2m21s

Verify the Pods:

# List pods in the "example-deployment" namespace
kubectl get pods -o wide -n example-deployment

# Shell output:
NAME                      READY   STATUS    RESTARTS   AGE     IP           NODE      NOMINATED NODE   READINESS GATES
example-daemonset-4zhgx   1/1     Running   0          2m31s   10.42.3.31   ubuntu4   <none>           <none>
example-daemonset-lsqrr   1/1     Running   0          2m31s   10.42.0.30   ubuntu1   <none>           <none>
example-daemonset-lwzdv   1/1     Running   0          2m31s   10.42.2.30   ubuntu3   <none>           <none>
example-daemonset-tk26c   1/1     Running   0          2m31s   10.42.1.29   ubuntu2   <none>           <none>

Verify all Resources:

# List resources in the "example-deployment" namespace
kubectl get all -n example-deployment

# Shell output:
NAME                          READY   STATUS    RESTARTS   AGE
pod/example-daemonset-4zhgx   1/1     Running   0          2m45s
pod/example-daemonset-lsqrr   1/1     Running   0          2m45s
pod/example-daemonset-lwzdv   1/1     Running   0          2m45s
pod/example-daemonset-tk26c   1/1     Running   0          2m45s

NAME                               DESIRED   CURRENT   READY   UP-TO-DATE   AVAILABLE   NODE SELECTOR   AGE
daemonset.apps/example-daemonset   4         4         4       4            4           <none>          2m45s

Delete DaemonSet
# 

# Delete the DaemonSet
kubectl delete daemonset example-daemonset -n example-deployment

Example DaemonSet (With Node Selection)
#

Label Kubernetes Nodes
#

List the Kubernetes nodes:

# List nodes
kubectl get nodes -o wide

# Shell output:
NAME      STATUS   ROLES                  AGE   VERSION        INTERNAL-IP     EXTERNAL-IP   OS-IMAGE             KERNEL-VERSION     CONTAINER-RUNTIME
ubuntu1   Ready    control-plane,master   10d   v1.30.5+k3s1   192.168.30.10   <none>        Ubuntu 24.04.1 LTS   6.8.0-45-generic   containerd://1.7.21-k3s2
ubuntu2   Ready    worker                 10d   v1.30.5+k3s1   192.168.30.11   <none>        Ubuntu 24.04.1 LTS   6.8.0-45-generic   containerd://1.7.21-k3s2
ubuntu3   Ready    worker                 10d   v1.30.5+k3s1   192.168.30.12   <none>        Ubuntu 24.04.1 LTS   6.8.0-45-generic   containerd://1.7.21-k3s2
ubuntu4   Ready    worker                 10d   v1.30.5+k3s1   192.168.30.13   <none>        Ubuntu 24.04.1 LTS   6.8.0-45-generic   containerd://1.7.21-k3s2

Label Kubernetes nodes:

# Label some of the Kubernetes nodes
kubectl label node ubuntu2 monitoring-enabled=true
kubectl label node ubuntu3 monitoring-enabled=true

Verify Node Labels:
# 

# List "monitoring-enabled" label
kubectl get nodes -o custom-columns=NAME:.metadata.name,MONITORING-ENABLED:.metadata.labels.monitoring-enabled

# Shell output:
NAME      MONITORING-ENABLED
ubuntu1   <none>
ubuntu2   true
ubuntu3   true
ubuntu4   <none>

Example Deployment
# 

# Create a manifest for the deployment
vi example-daemonset.yaml

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: example-daemonset
  namespace: example-deployment
spec:
  selector:
    matchLabels:
      app: some-pod
  template:
    metadata:
      labels:
        app: some-pod
    spec:
      nodeSelector:
        monitoring-enabled: "true"
      containers:
        - name: busybox
          image: busybox:latest
          command: ['sh', '-c', 'tail -f /dev/null']
          imagePullPolicy: IfNotPresent
      restartPolicy: Always

# Apply the manifest
kubectl apply -f example-daemonset.yaml

Verify Deployment
#

Verify the ReplicaSet:

# List the DaemonSet in the "example-deployment" namespace
kubectl get daemonset -n example-deployment

# Shell output:
NAME                DESIRED   CURRENT   READY   UP-TO-DATE   AVAILABLE   NODE SELECTOR             AGE
example-daemonset   2         2         2       2            2           monitoring-enabled=true   6s

Verify the Pods:

# List pods in the "example-deployment" namespace
kubectl get pods -o wide -n example-deployment

# Shell output:
NAME                      READY   STATUS    RESTARTS   AGE   IP           NODE      NOMINATED NODE   READINESS GATES
example-daemonset-526v9   1/1     Running   0          18s   10.42.1.30   ubuntu2   <none>           <none>
example-daemonset-mt5q6   1/1     Running   0          18s   10.42.2.31   ubuntu3   <none>           <none>

Verify all Resources:

# List resources in the "example-deployment" namespace
kubectl get all -n example-deployment

# Shell output:
NAME                          READY   STATUS    RESTARTS   AGE
pod/example-daemonset-526v9   1/1     Running   0          37s
pod/example-daemonset-mt5q6   1/1     Running   0          37s

NAME                               DESIRED   CURRENT   READY   UP-TO-DATE   AVAILABLE   NODE SELECTOR             AGE
daemonset.apps/example-daemonset   2         2         2       2            2           monitoring-enabled=true   37s

Delete DaemonSet
# 

# Delete the DaemonSet
kubectl delete daemonset example-daemonset -n example-deployment

Kubernetes-Components - This article is part of a series.
Part 1: Kubernetes Configuration Manifests: Create Manifests from RAW Output and Dry-Run Command
Part 2: Kubernetes Non-Disruptive & Disruptive Configuration Updates: Kubectl Apply, Edit, Patch & Replace; Update Rollouts and Rollbacks with Set Image Command
Part 3: Kubernetes Pods: Create Pods with Run-Command and YAML Configuration; Single & Multi Container Pods, Port-Forwarding, Find Container on Worker Node
Part 4: Kubernetes Pods: Init & Sidecar Container Overview, Init Container Examples
Part 5: Kubernetes Kubernetes Deployments & Replication Controllers (Soon Depricated): Example Deployment with Create-Command and YAML Configuration, Scale the Deployment; Example Replication Controller
Part 6: Kubernetes Services: Example ClusterIP, NodePort & LoadBalancer Services with Expose-Command and YAML Configuration; Service for External Endpoint
Part 7: Kubernetes Resource Management: Deploy Kubernetes Metrics Server, Vish/Stress Container Example, Define Resource Requests and Limits, Verify Resource Usage with kubectl top, Define a LimitRange for a Namespace
Part 8: Kubernetes Monitoring & Logs: Monitor Applications with top, Monitor Events Pod specific and Cluster wide, Container STDOUT and STDERR Logs
Part 9: Kubernetes Security: Immutable Deployment - Deploy Container with ReadOnly-Filesystem and Writable-Volume
Part 10: Kubernetes Security: Pod Security Admission (PSA) - Overview, Enforce Pod Security Standard at a Namespace; Example Nginx Pod SecurityContext for Restricted PSS
Part 11: Kubernetes Volumes: Nginx Pod and Deployment Examples with NFS Volume, Pod and Deployment Examples with EmptyDir Volume, Deployment Example with PersistentVolume, External Storage Provider with NFS
Part 12: Kubernetes Secrets: Opaque Secret Configuration, Pod Examples with Environment Variable Secrets and Volume Secrets; SSH Authentication Secret with Pod Example
Part 13: Kubernetes ConfigMaps: Mount ConfigMap to Pod as Volume, Mount ConfigMap as Environment Variable
Part 14: This Article
Part 15: Kubernetes Sets - StatefulSets: Difference between StatefulSet & ReplcaSet; StatefulSet Example with VolumeClaimTemplate and Stateless Service
Part 16: Kubernetes Labels, Annotations, Affinity / Anti-Affinity, Taints & Tolerations: Node Labeling, Pod Labeling & NodeSelector; Pod Annotations; Node Affinity, Pod Anti-Affinity; Node Taints and Pod Tolerations
Part 17: Kubernetes Configuration Management - Helm Charts: Create a Custom Helm Chart
Part 18: Kubernetes Configuration Management - Kustomize: Kustomize Example
Part 19: Kubernetes Networking - Network Policies: Ingress and Egress Policy Examples
Part 20: Kubernetes Networking - Liveness, Readiness & Startup Probe Examples: Liveness Probe (TCP), Readiness Probes (TCP / Single Pod and Multi Pod Dependency), Startup Probe (Command, TCP & HTTP)
Part 21: Kubernetes Networking - DNS: CoreDNS custom Hosts entry (K3s & K8s Version), Deployment with custom Hosts entry; Backup and Restore the CoreDNS ConfigMap; DNS Troubleshooting
Part 22: Kubernetes Horizontal Pod Autoscaling: Install Kubernetes Metrics Server, Example Deployment with Horizontal Pod Autoscaler (HPA)
Part 23: Kubernetes Jobs: Jobs Overview, Basic Non-parallel & Parallel Job Examples; CronJob & RBAC Example that Restarts a Deployment
Part 24: Kubernetes Role Based Access Control (RBAC): RBAC Overview, Create Service Account, Example Role and RoleBinding
Part 25: Kubernetes Kubeconfig: Create example Kubeconfig with new (RBAC) Service Account and ClusterRole / ClusterRole Binding
Part 26: Kubernetes Etcd Snapshot: Etcd Snapshot and Restore with Etcdctl, Verify Etcd Member Health; Etcdctl Commands
Part 27: Kubernetes Troubleshooting: Cluster, Nodes, Pods & Kubelet
Part 28: Kubernetes Commands: Kubectl Autocomplete, Cluster Nodes, Namespaces, LimitRange Resource Limits, Pods, Deployments, Replication Controllers, Services, HPA, Secrets, Cronjobs, Helm, Logs, K9s TUI