How to scale an OpenShift v4 cluster

Overview

In OpenShift v4 clusters, worker nodes are managed by "MachineSets". These are objects that define the configuration of worker nodes, and can be scaled to set the number of workers of that type in the cluster.

Scaling an OpenShift v4 cluster

To view available MachineSets and their current scale, check the Compute ... MachineSets section of the OpenShift web console, or run the following oc command:

oc get MachineSets -n openshift-machine-api

To scale a MachineSet up or down, set the scale against the MachineSet in the OpenShift web console, or run:

oc scale MachineSet <machinesetname> -n openshift-machine-api --replicas=<scale>

Where <machinesetname> is the name of the MachineSet to scale, and <scale> is the number of workers desired from that MachineSet.

After approximately three minutes, the new nodes should be visible in the OpenShift web console or in the output of:

oc get nodes
Note

When you scale down a MachineSet, some workers will be drained and deleted. Workloads will automatically restart on remaining nodes if sufficient capacity remains. If all worker MachineSets are scaled to "0", workloads may stop completely.

Default MachineSets available

UKCloud offers three charging models for OpenShift workers:

  • Hourly - This is charged by the hour, with a one hour minimum charge.

  • Monthly - This is charged by the month, with a one month minimum charge. However, when used for the entire month, the cost is lower than running a hourly worker for the entire month.

  • Annual - This is charged by the year, with a one year minimum charge. However, when used for the entire year, the cost is lower than running a monthly worker for the entire year. If you'd like to add annual MachineSets to your cluster, raise a Service Request via the My Calls section of the UKCloud Portal and provide us with the size and network connectivity of the MachineSets you'd like to add.

Hourly MachineSets are particularly useful for short-term testing or for bursts of demand.

By default, UKCloud OpenShift clusters have the following MachineSets available:

  • <clusterid>-hourly-m1-medium - 4 CPU, 16GB RAM, charged by the hour

  • <clusterid>-monthly-m1-medium - 4 CPU, 16GB RAM, charged by the month

  • <clusterid>-hourly-r1-small - 8 CPU, 16GB RAM, charged by the hour

  • <clusterid>-monthly-r1-small - 8 CPU, 16GB RAM, charged by the month

  • <clusterid>-hourly-m1-large - 4 CPU, 32B RAM, charged by the hour

  • <clusterid>-monthly-m1-large - 4 CPU, 32GB RAM, charged by the month

  • <clusterid>-hourly-r1-medium - 8 CPU, 32GB RAM, charged by the hour

  • <clusterid>-monthly-r1-medium - 8 CPU, 32GB RAM, charged by the month

For information about costs for each flavour and charging model, see section 2.1.3 of the UKCloud Pricing Guide.

Note

UKCloud can add MachineSets for larger node flavours. If this is something you require, raise a Service Request via the My Calls section of the UKCloud Portal and provide us with the size and network connectivity of the MachineSets you'd like to add.

Further information

For more information, see the Red Hat OpenShift Documentation: https://docs.openshift.com/container-platform/4.8/machine_management/manually-scaling-machineset.html

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