How to update a Kubernetes DaemonSet image?

Introduction

In this tutorial, we will explore the process of updating the image of a Kubernetes DaemonSet. DaemonSets are a powerful Kubernetes resource that ensure a specific pod runs on all (or a selection of) nodes in a cluster. Keeping the images used by your DaemonSets up-to-date is crucial for maintaining the security and functionality of your Kubernetes-based applications.

Skills Graph

Understanding Kubernetes DaemonSets

What is a Kubernetes DaemonSet?

A Kubernetes DaemonSet is a type of Kubernetes workload that ensures a copy of a Pod is running on every (or a selection of) nodes in a Kubernetes cluster. DaemonSets are useful for running system daemons, such as log collectors, monitoring agents, or other infrastructure-related applications, on all (or a subset of) nodes in a cluster.

Key Characteristics of DaemonSets

• Ensures a Pod is running on every node (or a subset): When a new node is added to the cluster, a Pod from the DaemonSet is automatically scheduled on that node. Similarly, when a node is removed from the cluster, the Pod is garbage collected.
• Allows selective scheduling: DaemonSets can be configured to run Pods on only a subset of nodes based on labels or other node selectors.
• Provides a way to run system daemons: DaemonSets are commonly used to run system-level applications, such as log collectors, monitoring agents, and other infrastructure-related services, across the entire cluster.
• Ensures high availability: By running a copy of a Pod on every node, DaemonSets help ensure that the system-level services are highly available and can quickly respond to issues on any node.

Advantages of Using DaemonSets

• Automatic scheduling: DaemonSets automatically schedule Pods on new nodes and remove them from nodes that are being decommissioned.
• Consistent deployment: DaemonSets ensure that a specific system-level service is running on all (or a subset of) nodes in the cluster.
• High availability: DaemonSets help maintain the availability of system-level services by running a copy of the Pod on every node.
• Scalability: As the cluster grows, DaemonSets automatically scale to maintain the desired state across all nodes.

DaemonSet Use Cases

• Logging and monitoring: Running log collectors and monitoring agents as DaemonSets ensures that these services are present on all nodes, providing comprehensive monitoring and logging capabilities.
• Network plugins: Network plugins, such as Flannel or Calico, are often deployed as DaemonSets to ensure that the network infrastructure is set up correctly on all nodes.
• Storage plugins: Storage plugins, like the Ceph or Gluster agents, can be deployed as DaemonSets to provide distributed storage access across the cluster.
• Hardware management: DaemonSets can be used to run hardware management tools, such as node exporter or GPU device plugins, on all (or a subset of) nodes.

Updating a DaemonSet Image

Updating the DaemonSet Image

To update the image of a DaemonSet, you can use the kubectl set image command. This command allows you to update the image of a specific container within a DaemonSet.

Here's an example of how to update the image of a DaemonSet:

kubectl set image daemonset/<daemonset-name> <container-name>=<new-image-name> --record

Replace the following:

• <daemonset-name>: the name of the DaemonSet you want to update
• <container-name>: the name of the container within the DaemonSet you want to update
• <new-image-name>: the new image you want to use for the container

The --record flag is optional, but it's recommended to include it as it will add the command as an annotation to the resource, making it easier to track changes.

Verifying the Image Update

After updating the DaemonSet image, you can verify the update by checking the status of the DaemonSet and the Pods it manages.

1. Check the DaemonSet status:

kubectl get daemonset <daemonset-name>

This will show you the current image being used by the DaemonSet.

2. Check the status of the Pods:

kubectl get pods -l app=<daemonset-name>

This will list all the Pods managed by the DaemonSet, and you can inspect the image being used by each Pod.

You can also use the kubectl describe command to get more detailed information about the DaemonSet and its Pods:

kubectl describe daemonset <daemonset-name>

This will show you the current and previous image versions used by the DaemonSet.

Rollback Image Updates

If you need to roll back to a previous image version, you can use the kubectl rollout undo command:

kubectl rollout undo daemonset/<daemonset-name>

This will revert the DaemonSet to the previous image version.

Verifying the Image Update

Checking the DaemonSet Status

After updating the DaemonSet image, you can verify the update by checking the status of the DaemonSet and the Pods it manages. You can use the kubectl get command to check the DaemonSet status:

kubectl get daemonset <daemonset-name>

This will show you the current image being used by the DaemonSet.

Inspecting the Pods

To check the status of the Pods managed by the DaemonSet, you can use the following command:

kubectl get pods -l app=<daemonset-name>

This will list all the Pods managed by the DaemonSet, and you can inspect the image being used by each Pod.

Detailed DaemonSet Information

You can also use the kubectl describe command to get more detailed information about the DaemonSet and its Pods:

kubectl describe daemonset <daemonset-name>

This will show you the current and previous image versions used by the DaemonSet, as well as other details about the DaemonSet and its Pods.

Verifying the Image Update in the Pods

To verify that the image update has been applied to the Pods, you can check the image used by each Pod. You can do this by inspecting the Pod's container image:

kubectl get pods -l app= jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.spec.containers[0].image}{"\n"}{end}' < daemonset-name > -o

This command will list the name of each Pod and the image being used by the first container in the Pod.

By comparing the image versions, you can confirm that the DaemonSet image update has been successfully applied to all the Pods.

Summary

By the end of this Kubernetes tutorial, you will have learned how to update the image of a DaemonSet, ensuring your applications stay current and secure. This knowledge will empower you to effectively manage your Kubernetes deployments and maintain the reliability of your Kubernetes-based infrastructure.