Isolating Infrastructure Nodes

Applying a specific node selector to all infrastructure components will guarantee that they will be scheduled on nodes with that label. See more details on node selectors in placing pods on specific nodes using node selectors, and about node labels in understanding how to update labels on nodes.

Our node label and matching selector for infrastructure components will be node-role.kubernetes.io/infra: "".

To prevent other workloads from also being scheduled on those infrastructure nodes, we need one of two solutions:

• Apply a taint to the infrastructure nodes and tolerations to the desired infrastructure workloads.
  OR
• Apply a completely separate label to your other nodes and matching node selector to your other workloads such that they are mutually exclusive from infrastructure nodes.

TIP: To ensure High Availability (HA) each cluster should have three Infrastructure nodes, ideally across availability zones. See more details about rebooting nodes running critical infrastructure.

TIP: Review the infrastructure node sizing suggestions

By default all nodes except for masters will be labeled with node-role.kubernetes.io/worker: "". We will be adding node-role.kubernetes.io/infra: "" to infrastructure nodes.

However, if you want to remove the existing worker role from your infra nodes, you will need an MCP to ensure that all the nodes upgrade correctly. This is because the worker MCP is responsible for updating and upgrading the nodes, and it finds them by looking for this node-role label. If you remove the label, you must have a MachineConfigPool that can find your infra nodes by the infra node-role label instead. Previously this was not the case and removing the worker label could have caused issues in OCP <= 4.3.

This infra MCP definition below will find all MachineConfigs labeled both “worker” and “infra” and it will apply them to any Machines or Nodes that have the “infra” role label. In this manner, you will ensure that your infra nodes can upgrade without the “worker” role label.

apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfigPool
metadata:
  name: infra
spec:
  machineConfigSelector:
    matchExpressions:
      - {key: machineconfiguration.openshift.io/role, operator: In, values: [worker,infra]}
  nodeSelector:
    matchLabels:
      node-role.kubernetes.io/infra: ""

If you are not using the MachineSet API to manage your nodes, labels and taints are applied manually to each node:

Label it:

oc label node <node-name> node-role.kubernetes.io/infra=
oc label node <node-name> node-role.kubernetes.io=infra

Taint it:

oc adm taint nodes -l node-role.kubernetes.io/infra node-role.kubernetes.io/infra=reserved:NoSchedule node-role.kubernetes.io/infra=reserved:NoExecute