Posted on Jul 7, 2024

Mastering Kubernetes DaemonSets: Deploy Pods Across Your Cluster

#coding #programming #tutorial #kubernetes

Introduction

This article covers the following tech skills:

In Kubernetes, a DaemonSet is a type of controller that ensures a copy of a pod is running on every node in the cluster. This lab will guide you through the process of creating a DaemonSet to run replicas of a pod on every node in the cluster.

Create a Pod

Create a simple pod that will be used as the template for the replicas. Create a file called /home/labex/project/myapp-pod.yaml with the following contents:

apiVersion: v1 kind: Pod metadata: name: myapp-pod spec: containers: - name: myapp-container image: nginx ports: - containerPort: 80

Create the pod using the following command:

kubectl apply -f /home/labex/project/myapp-pod.yaml

Create a Daemonset

Create a DaemonSet to run replicas of the myapp-pod on every node in the cluster. Create a file called /home/labex/project/myapp-daemonset.yaml with the following contents:

apiVersion: apps/v1 kind: DaemonSet metadata: name: myapp-daemonset spec: selector: matchLabels: app: myapp template: metadata: labels: app: myapp spec: containers: - name: myapp-container image: nginx ports: - containerPort: 80

This DaemonSet uses the myapp-pod as the template for the replicas and sets the matchLabels selector to app: myapp to ensure that the replicas are created on every node.

Create the DaemonSet using the following command:

kubectl apply -f /home/labex/project/myapp-daemonset.yaml

Verify the Daemonset

Verify that the DaemonSet has been created and that replicas of the myapp-pod are running on every node. Use the following command to list the nodes in the cluster:

kubectl get nodes

Use the following command to list the pods created by the DaemonSet:

kubectl get pods -l app=myapp

You should see one pod for each node in the cluster.

Update the Daemonset

Update the DaemonSet to change the image used by the myapp-container. Create a file called /home/labex/project/myapp-daemonsett-update.yaml with the following contents:

apiVersion: apps/v1 kind: DaemonSet metadata: name: myapp-daemonset spec: selector: matchLabels: app: myapp template: metadata: labels: app: myapp spec: containers: - name: myapp-container image: busybox command: ["sleep", "3600"]

This updated DaemonSet changes the image used by the myapp-container to busybox and sets the command to sleep 3600.

Update the DaemonSet using the following command:

kubectl apply -f /home/labex/project/myapp-daemonset-update.yaml

Verify that the DaemonSet has been updated and that replicas of the myapp-pod are running with the new image. Use the following command to list the pods created by the DaemonSet: