16 Deploying node agents and daemons with DaemonSets
This chapter covers
- Running an agent Pod on each cluster node
- Running agent Pods on a subset of nodes
- Allowing Pods to access the host node’s resources
- Assigning a priority class to a Pod
- Communicating with the local agent Pod
In the previous chapters, you learned how to use Deployments or StatefulSets to distribute multiple replicas of a workload across the nodes of your cluster. But what if you want to run exactly one replica on each node? For example, you might want each node to run an agent or daemon that provides a system service such as metrics collection or log aggregation for that node. To deploy these types of workloads in Kubernetes, you use a DaemonSet.
Before you begin, create the kiada Namespace, change to the Chapter16/ directory, and apply all manifests in the SETUP/ directory by running the following commands:
$ kubectl create ns kiada $ kubectl config set-context --current --namespace kiada $ kubectl apply -f SETUP -R
NOTE
You can find the code files for this chapter at https://github.com/luksa/kubernetes-in-action-2nd-edition/tree/master/Chapter16.
16.1 Introducing DaemonSets
A DaemonSet is an API object that ensures that exactly one replica of a Pod is running on each cluster node. By default, daemon Pods are deployed on every node, but you can use a node selector to restrict deployment to some of the nodes.