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Adding infrastructure nodes to an ARO cluster

Authors: Paul Czarkowski
Last Editor: Dustin Scott
Published Date: 17 August 2022
Modified Date: 25 May 2023

This document shows how to set up infrastructure nodes in an ARO cluster and move infrastructure related workloads to them. This can help with larger clusters that have resource contention between user workloads and infrastructure workloads such as Prometheus.

Important note: Infrastructure nodes are billed at the same rates as your existing ARO worker nodes.

You can find the original (and more detailed) document describing the process for a self-managed OpenShift Container Platform cluster here

Prerequisites

Create Infra Nodes

We’ll use the MOBB Helm Chart for adding ARO machinesets which defaults to creating infra nodes, it looks up an existing machineset to collect cluster specific settings and then creates a new machineset specific for infra nodes with the same settings.

  1. Add the MOBB chart repository to your Helm

    helm repo add mobb https://rh-mobb.github.io/helm-charts/

  2. Update your repositories

    helm repo update

  3. Install the mobb/aro-machinesets Chart to create infra nodes

    helm upgrade --install -n openshift-machine-api \
  infra mobb/aro-machinesets

  4. Wait for the new nodes to be available

    watch oc get machines

Moving Infra workloads

Ingress

You may choose this for any additional Ingress controllers you may have in the cluster, however if you application has very high Ingress resource requirements it may make sense to allow them to spread across the worker nodes, or even a dedicated MachineSet.

  1. Set the nodePlacement on the ingresscontroller to node-role.kubernetes.io/infra and increase the replicas to match the number of infra nodes

    oc patch -n openshift-ingress-operator ingresscontroller default --type=merge  \
   -p='{"spec":{"replicas":3,"nodePlacement":{"nodeSelector":{"matchLabels":{"node-role.kubernetes.io/infra":""}},"tolerations":[{"effect":"NoSchedule","key":"node-role.kubernetes.io/infra","operator":"Exists"}]}}}'

  2. Check the Ingress Controller Operator is starting pods on the new infra nodes

    oc -n openshift-ingress get pods -o wide

    NAME                              READY   STATUS        RESTARTS   AGE   IP            NODE                                                    NOMINATED NODE   READINESS GATES
router-default-69f58645b7-6xkvh   1/1     Running       0          66s   10.129.6.6    cz-cluster-hsmtw-infra-aro-machinesets-eastus-3-l6dqw   <none>           <none>
router-default-69f58645b7-vttqz   1/1     Running       0          66s   10.131.4.6    cz-cluster-hsmtw-infra-aro-machinesets-eastus-1-vr56r   <none>           <none>
router-default-6cb5ccf9f5-xjgcp   1/1     Terminating   0          23h   10.131.0.11   cz-cluster-hsmtw-worker-eastus2-xj9qx                   <none>           <none>

Registry

  1. Set the nodePlacement on the registry to node-role.kubernetes.io/infra

    oc patch configs.imageregistry.operator.openshift.io/cluster --type=merge \
  -p='{"spec":{"affinity":{"podAntiAffinity":{"preferredDuringSchedulingIgnoredDuringExecution":[{"podAffinityTerm":{"namespaces":["openshift-image-registry"],"topologyKey":"kubernetes.io/hostname"},"weight":100}]}},"logLevel":"Normal","managementState":"Managed","nodeSelector":{"node-role.kubernetes.io/infra":""},"tolerations":[{"effect":"NoSchedule","key":"node-role.kubernetes.io/infra","operator":"Exists"}]}}'

  2. Check the Registry Operator is starting pods on the new infra nodes

    oc -n openshift-image-registry get pods -l "docker-registry" -o wide

    NAME                              READY   STATUS    RESTARTS   AGE     IP           NODE                                                    NOMINATED NODE   READINESS GATES
image-registry-84cbd76d5d-cfsw7   1/1     Running   0          3h46m   10.128.6.7   cz-cluster-hsmtw-infra-aro-machinesets-eastus-2-kljml   <none>           <none>
image-registry-84cbd76d5d-p2jf9   1/1     Running   0          3h46m   10.129.6.7   cz-cluster-hsmtw-infra-aro-machinesets-eastus-3-l6dqw   <none>           <none>

Cluster Monitoring

  1. Configure the cluster monitoring stack to use the infra nodes

    Note: This will override any other customizations to the cluster monitoring stack, so you may want to merge your existing customizations into this before running the command.

    cat << EOF | oc apply -f -
apiVersion: v1
kind: ConfigMap
metadata:
  name: cluster-monitoring-config
  namespace: openshift-monitoring
data:
  config.yaml: |+
    alertmanagerMain:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
      tolerations:
        - effect: "NoSchedule"
          key: "node-role.kubernetes.io/infra"
          operator: "Exists"
    prometheusK8s:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
      tolerations:
        - effect: "NoSchedule"
          key: "node-role.kubernetes.io/infra"
          operator: "Exists"
    prometheusOperator: {}
    grafana:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
      tolerations:
        - effect: "NoSchedule"
          key: "node-role.kubernetes.io/infra"
          operator: "Exists"
    k8sPrometheusAdapter:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
      tolerations:
        - effect: "NoSchedule"
          key: "node-role.kubernetes.io/infra"
          operator: "Exists"
    kubeStateMetrics:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
      tolerations:
        - effect: "NoSchedule"
          key: "node-role.kubernetes.io/infra"
          operator: "Exists"
    telemeterClient:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
      tolerations:
        - effect: "NoSchedule"
          key: "node-role.kubernetes.io/infra"
          operator: "Exists"
    openshiftStateMetrics:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
      tolerations:
        - effect: "NoSchedule"
          key: "node-role.kubernetes.io/infra"
          operator: "Exists"
    thanosQuerier:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
      tolerations:
        - effect: "NoSchedule"
          key: "node-role.kubernetes.io/infra"
          operator: "Exists"
EOF

  2. Check the OpenShift Monitoring Operator is starting pods on the new infra nodes

    some Pods like prometheus-operator will remain on master nodes.

    oc -n openshift-monitoring get pods -o wide

    NAME                                           READY   STATUS    RESTARTS   AGE     IP            NODE                                                    NOMINATED NODE   READINESS GATES
alertmanager-main-0                            6/6     Running   0          2m14s   10.128.6.11   cz-cluster-hsmtw-infra-aro-machinesets-eastus-2-kljml   <none>           <none>
alertmanager-main-1                            6/6     Running   0          2m46s   10.131.4.11   cz-cluster-hsmtw-infra-aro-machinesets-eastus-1-vr56r   <none>           <none>
cluster-monitoring-operator-5bbfd998c6-m9w62   2/2     Running   0          28h     10.128.0.23   cz-cluster-hsmtw-master-1                               <none>           <none>
grafana-599d4b948c-btlp2                       3/3     Running   0          2m48s   10.131.4.10   cz-cluster-hsmtw-infra-aro-machinesets-eastus-1-vr56r   <none>           <none>
kube-state-metrics-574c5bfdd7-f7fjk            3/3     Running   0          2m49s   10.131.4.8    cz-cluster-hsmtw-infra-aro-machinesets-eastus-1-vr56r   <none>           <none>
...
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