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Scaling Cluster Monitoring Operator

Overview

OKD exposes metrics that can be collected and stored in back-ends by the cluster-monitoring-operator. As an OKD administrator, you can view system resources, containers and components metrics in one dashboard interface, Grafana.

This topic provides information on scaling the cluster monitoring operator.

If you want to use Prometheus with persistent storage, you must set the openshift_cluster_monitoring_operator_prometheus_storage_enabled variable in your Ansible inventory file to true.

Recommendations for OKD

Capacity Planning for Cluster Monitoring Operator

Various tests were performed for different scale sizes. The Prometheus database grew, as reflected in the table below.

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 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

In the above calculation, 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 was developed for the default OKD cluster-monitoring-operator. For higher scale, edit the openshift_cluster_monitoring_operator_prometheus_storage_capacity variable in the Ansible inventory file, which defaults to 50Gi.

CPU utilization has minor impact. The ratio is approximately 1 core out of 40 per 50 nodes and 1800 pods.

Lab Environment

All experiments were performed in an OKD on OpenStack environment:

  • Infra nodes (VMs) - 40 cores, 157 GB RAM.

  • CNS nodes (VMs) - 16 cores, 62 GB RAM, NVMe drives.

Prerequisites

Based on your scale destination, compute and set the relevant PV size for the Prometheus data store. Since the default Prometheus pods replicas is 2, for 100 nodes with 3600 pods you will need 188 GB.

For example:

195 GB (space per 15 days ) * 2 (pods) = 390 GB free

Based on this equation, set openshift_cluster_monitoring_operator_prometheus_storage_capacity=195Gi.