daemon sets

In Kubernetes, a DaemonSet is a resource object that ensures that a specified Pod runs on all (or a specific subset of) nodes in a cluster. DaemonSets are useful for deploying background services, daemons, or system-level tasks that should run on every node in the cluster.

Here are key characteristics and use cases for DaemonSets:

1. One Pod Per Node:

   • A DaemonSet creates and maintains one instance (Pod) of the specified workload on each node in the cluster. If new nodes are added, DaemonSets automatically create Pods on those nodes. If nodes are removed, the DaemonSet terminates the corresponding Pods.

2. Background Services:

   • DaemonSets are commonly used for deploying background services or agents that need to run on every node, such as log collectors, monitoring agents, or network proxies.

3. Node-Level Operations:

   • DaemonSets are suitable for tasks that require node-level operations rather than coordination across the entire cluster.

4. Example DaemonSet Definition:

    yamlCopy codeapiVersion: apps/v1
    kind: DaemonSet
    metadata:
      name: example-daemonset
    spec:
      selector:
        matchLabels:
          app: example
      template:
        metadata:
          labels:
            app: example
        spec:
          containers:
          - name: example-container
            image: example-image:latest
   

   In this example, the DaemonSet ensures that one Pod with the label "app: example" runs on each node, and it uses a container with the specified image.

5. Rolling Updates:

   • DaemonSets support rolling updates. When you update the DaemonSet with a new version of the workload (e.g., a new container image), it automatically triggers a rolling update, terminating old Pods and creating new ones.

6. Node Affinity and Taints/Tolerations:

   • DaemonSets support node affinity rules and taints/tolerations, allowing you to control on which nodes the workload should run.

DaemonSets are a powerful resource for deploying and managing services that need to run on every node in a Kubernetes cluster. They simplify the deployment and scaling of background processes while ensuring that the specified workload is always present on each node.