Chapter 9. Scaling the Cluster Monitoring Operator OpenShift Container Platform exposes metrics that the Cluster Monitoring Operator collects and stores in the Prometheus-based monitoring stack. As an administrator, you can view system resources, containers and components metrics in one dashboard interface, Grafana. Important If you are running cluster monitoring with an attached PVC for Prometheus, you might experience OOM kills during cluster upgrade. When persistent storage is in use for Prometheus, Prometheus memory usage doubles during cluster upgrade and for several hours after upgrade is complete. To avoid the OOM kill issue, allow worker nodes with double the size of memory that was available prior to the upgrade. For example, if you are running monitoring on the minimum recommended nodes, which is 2 cores with 8 GB of RAM, increase memory to 16 GB. For more information, see BZ#1925061 . 9.1. Prometheus database storage requirements Red Hat performed various tests for different scale sizes. Note The Prometheus storage requirements below are not prescriptive. Higher resource consumption might be observed in your cluster depending on workload activity and resource use. Table 9.1. Prometheus Database storage requirements based on number of nodes/pods in the cluster Number of Nodes Number of pods Prometheus storage growth per day Prometheus storage growth per 15 days RAM Space (per scale size) Network (per tsdb chunk) 50 1800 6.3 GB 94 GB 6 GB 16 MB 100 3600 13 GB 195 GB 10 GB 26 MB 150 5400 19 GB 283 GB 12 GB 36 MB 200 7200 25 GB 375 GB 14 GB 46 MB Approximately 20 percent of the expected size was added as overhead to ensure that the storage requirements do not exceed the calculated value. The above calculation is for the default OpenShift Container Platform Cluster Monitoring Operator. Note CPU utilization has minor impact. The ratio is approximately 1 core out of 40 per 50 nodes and 1800 pods. Recommendations for OpenShift Container Platform Use at least three infrastructure (infra) nodes. Use at least three openshift-container-storage nodes with non-volatile memory express (NVMe) drives. 9.2. Configuring cluster monitoring You can increase the storage capacity for the Prometheus component in the cluster monitoring stack. Procedure To increase the storage capacity for Prometheus: Create a YAML configuration file, cluster-monitoring-config.yaml . For example: apiVersion: v1 kind: ConfigMap data: config.yaml: | prometheusK8s: retention: {{PROMETHEUS_RETENTION_PERIOD}} 1 nodeSelector: node-role.kubernetes.io/infra: "" volumeClaimTemplate: spec: storageClassName: {{STORAGE_CLASS}} 2 resources: requests: storage: {{PROMETHEUS_STORAGE_SIZE}} 3 alertmanagerMain: nodeSelector: node-role.kubernetes.io/infra: "" volumeClaimTemplate: spec: storageClassName: {{STORAGE_CLASS}} 4 resources: requests: storage: {{ALERTMANAGER_STORAGE_SIZE}} 5 metadata: name: cluster-monitoring-config namespace: openshift-monitoring 1 A typical value is PROMETHEUS_RETENTION_PERIOD=15d . Units are measured in time using one of these suffixes: s, m, h, d. 2 4 The storage class for your cluster. 3 A typical value is PROMETHEUS_STORAGE_SIZE=2000Gi . Storage values can be a plain integer or as a fixed-point integer using one of these suffixes: E, P, T, G, M, K. You can also use the power-of-two equivalents: Ei, Pi, Ti, Gi, Mi, Ki. 5 A typical value is ALERTMANAGER_STORAGE_SIZE=20Gi . Storage values can be a plain integer or as a fixed-point integer using one of these suffixes: E, P, T, G, M, K. You can also use the power-of-two equivalents: Ei, Pi, Ti, Gi, Mi, Ki. Add values for the retention period, storage class, and storage sizes. Save the file. Apply the changes by running: USD oc create -f cluster-monitoring-config.yaml

Commands:
apiVersion: v1 kind: ConfigMap data: config.yaml: | prometheusK8s: retention: {{PROMETHEUS_RETENTION_PERIOD}} 1 nodeSelector: node-role.kubernetes.io/infra: "" volumeClaimTemplate: spec: storageClassName: {{STORAGE_CLASS}} 2 resources: requests: storage: {{PROMETHEUS_STORAGE_SIZE}} 3 alertmanagerMain: nodeSelector: node-role.kubernetes.io/infra: "" volumeClaimTemplate: spec: storageClassName: {{STORAGE_CLASS}} 4 resources: requests: storage: {{ALERTMANAGER_STORAGE_SIZE}} 5 metadata: name: cluster-monitoring-config namespace: openshift-monitoring
oc create -f cluster-monitoring-config.yaml