A daemon set ensures that all eligible nodes run a copy of a pod. Normally, the node that a pod runs on is selected by the Kubernetes scheduler. However, daemon set pods are created and scheduled by the daemon set controller. That introduces the following issues:
Inconsistent pod behavior: Normal pods waiting to be scheduled are created and in Pending state, but daemon set pods are not created in
Pending state. This is confusing to the user.
Pod preemption is handled by default scheduler. When preemption is enabled, the daemon set controller will make scheduling decisions without considering pod priority and preemption.
The ScheduleDaemonSetPods feature, enabled by default in OKD, lets you schedule daemon sets using the default scheduler instead of the daemon set controller, by adding the
NodeAffinity term to the daemon set pods, instead of the
spec.nodeName term. The default scheduler is then used to bind the pod to the target host. If node affinity of the daemon set pod already exists, it is replaced. The daemon set controller only performs these operations when creating or modifying daemon set pods, and no changes are made to the
spec.template of the daemon set.
- key: metadata.name
In addition, a
node.kubernetes.io/unschedulable:NoSchedule toleration is added automatically to daemon set pods. The default scheduler ignores unschedulable Nodes when scheduling daemon set pods.