13장. Nodes

When you deploy OpenShift Container Platform on bare metal infrastructure, there are additional considerations that must be taken into account compared to deploying on cloud infrastructure.

Unlike in cloud environments where the cluster nodes are considered ephemeral, re-provisioning a bare-metal node requires significantly more time and effort for maintenance tasks.

When a bare-metal node fails, for example, if a an unrecoverable kernel error happens or a NIC card hardware failure occurs, workloads on the failed node need to be restarted elsewhere else on the cluster while the problem node is repaired or replaced. Node maintenance mode allows cluster administrators to gracefully power down nodes, moving workloads to other parts of the cluster and ensuring workloads do not get interrupted. Detailed progress and node status details are provided during maintenance.

The Node Maintenance Operator watches for new or deleted NodeMaintenance custom resources (CRs). When a new NodeMaintenance CR is detected, no new workloads are scheduled, and the node is cordoned off from the rest of the cluster. All pods that can be evicted are evicted from the node. When a NodeMaintenance CR is deleted, the node that is referenced in the CR is made available for new workloads.

Using a NodeMaintenance CR for node maintenance tasks achieves the same results as the oc adm cordon and oc adm drain commands using standard OpenShift Container Platform custom resource processing.