When managing containerized applications in Kubernetes, certain scenarios require running a Pod on every Node in the cluster. This is where Kubernetes DaemonSet comes into play. A DaemonSet ensures that a specific Pod is always running on all or selected Nodes, making it an essential resource for system-level applications, monitoring agents, and log collectors. In this article, we’ll dive into what DaemonSet is, its use cases, how to set it up, and best practices to follow.

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What is a Kubernetes DaemonSet?

A DaemonSet is a kubernetes daemonset that ensures all or selected Nodes run a Pod. As new Nodes are added to the cluster, DaemonSet automatically deploys the Pod to them. Conversely, when Nodes are removed, the corresponding Pods are also terminated.

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Key Use Cases for DaemonSet

1. Monitoring and Logging: Deploy agents like Prometheus Node Exporter, Fluentd, or Filebeat on every Node.
2. System Services: Run system-level applications, such as network plugins or storage daemons.
3. Security Agents: Install intrusion detection systems or vulnerability scanners across all Nodes.
4. Custom Resource Management: Manage custom resources or perform maintenance tasks on every Node.

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How Does DaemonSet Work?

When you create a DaemonSet, it:

• Schedules Pods on all available Nodes in the cluster.
• Maintains Pod Consistency: If a Node fails, the DaemonSet re-creates the Pod on a new Node.
• Automatic Scaling: As new Nodes are added to the cluster, DaemonSet deploys the Pod automatically.

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Setting Up a DaemonSet in Kubernetes

Here’s a quick guide to creating a DaemonSet:

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Best Practices for Using Kubernetes DaemonSet

1. Limit Node Selection: Use nodeSelectors or nodeAffinity to target specific Nodes.
2. Resource Management: Set resource requests and limits to avoid Node resource exhaustion.
3. Rolling Updates: Implement rolling updates to avoid downtime.
4. Monitoring: Regularly check Pod status with kubectl get pods -o wide.
5. Labeling and Tainting: Utilize Node labels and taints to refine Pod scheduling.

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Pros and Cons of DaemonSet

Pros:

• Automatic Scheduling: Simplifies Pod deployment across all Nodes.
• High Availability: Ensures Pods are redundant and resilient.
• Low Maintenance: Automatically handles Node additions and removals.

Cons:

• Resource Intensive: Can overwhelm Nodes if not managed properly.
• Limited Use Cases: Primarily suited for system-level applications.
• Update Complexity: Rolling updates may cause service disruptions if not carefully managed.

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When to Use DaemonSet vs. Deployment?

While DaemonSet is ideal for Node-specific services, Deployments are better for stateless applications where Pod scaling is required. Use DaemonSet for monitoring, logging, and system agents, and Deployment for web applications or business logic containers.

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Troubleshooting Common Issues

• Pods Not Scheduling: Check Node selectors, taints, and tolerations.
• Pods Not Starting: Review Pod logs using:

bash

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kubectl logs <pod-name>

• DaemonSet Not Updating: Ensure rollingUpdate strategy is correctly configured in the spec.

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Conclusion

Kubernetes DaemonSet is a powerful tool for deploying system-critical Pods on all Nodes in your cluster. It is ideal for monitoring, logging, and running Node-specific applications. By following best practices and carefully managing resource allocation, you can ensure a stable and efficient Kubernetes environment.

Whether you’re setting up log collectors, security agents, or system daemons, a well-configured DaemonSet can make Node management easier and more effective. Start implementing DaemonSets in your Kubernetes cluster today to streamline your infrastructure management!