Manually scaling a machine set | Machine management | OpenShift Container Platform 4.10

Prerequisites
Scaling a machine set manually
The machine set deletion policy

You can add or remove an instance of a machine in a machine set.

If you need to modify aspects of a machine set outside of scaling, see Modifying a machine set.

Prerequisites

If you enabled the cluster-wide proxy and scale up workers not included in networking.machineNetwork[].cidr from the installation configuration, you must add the workers to the Proxy object’s noProxy field to prevent connection issues.

You can use the advanced machine management and scaling capabilities only in clusters where the Machine API is operational. Clusters with user-provisioned infrastructure require additional validation and configuration to use the Machine API.

Clusters with the infrastructure platform type none cannot use the Machine API. This limitation applies even if the compute machines that are attached to the cluster are installed on a platform that supports the feature. This parameter cannot be changed after installation.

To view the platform type for your cluster, run the following command:

$ oc get infrastructure cluster -o jsonpath='{.status.platform}'

Scaling a machine set manually

To add or remove an instance of a machine in a machine set, you can manually scale the machine set.

This guidance is relevant to fully automated, installer-provisioned infrastructure installations. Customized, user-provisioned infrastructure installations do not have machine sets.

Prerequisites

Install an OpenShift Container Platform cluster and the oc command line.
Log in to oc as a user with cluster-admin permission.

Procedure

View the machine sets that are in the cluster:
```
$ oc get machinesets -n openshift-machine-api
```
The machine sets are listed in the form of <clusterid>-worker-<aws-region-az>.

View the machines that are in the cluster:

$ oc get machine -n openshift-machine-api

Set the annotation on the machine that you want to delete:

$ oc annotate machine/<machine_name> -n openshift-machine-api machine.openshift.io/cluster-api-delete-machine="true"

Scale the compute machine set by running one of the following commands:

$ oc scale --replicas=2 machineset <machineset> -n openshift-machine-api

Or:

$ oc edit machineset <machineset> -n openshift-machine-api

You can alternatively apply the following YAML to scale the machine set:

apiVersion: machine.openshift.io/v1beta1
kind: MachineSet
metadata:
  name: <machineset>
  namespace: openshift-machine-api
spec:
  replicas: 2

You can scale the compute machine set up or down. It takes several minutes for the new machines to be available.

By default, the machine controller tries to drain the node that is backed by the machine until it succeeds. In some situations, such as with a misconfigured pod disruption budget, the drain operation might not be able to succeed. If the drain operation fails, the machine controller cannot proceed removing the machine.

You can skip draining the node by annotating machine.openshift.io/exclude-node-draining in a specific machine.

Verification

Verify the deletion of the intended machine:
```
$ oc get machines
```

The machine set deletion policy

Random, Newest, and Oldest are the three supported deletion options. The default is Random, meaning that random machines are chosen and deleted when scaling machine sets down. The deletion policy can be set according to the use case by modifying the particular machine set:

spec:
  deletePolicy: <delete_policy>
  replicas: <desired_replica_count>

Specific machines can also be prioritized for deletion by adding the annotation machine.openshift.io/cluster-api-delete-machine=true to the machine of interest, regardless of the deletion policy.

By default, the OpenShift Container Platform router pods are deployed on workers. Because the router is required to access some cluster resources, including the web console, do not scale the worker machine set to 0 unless you first relocate the router pods.

Custom machine sets can be used for use cases requiring that services run on specific nodes and that those services are ignored by the controller when the worker machine sets are scaling down. This prevents service disruption.