If you are not familiar with the oc command, refer to OpenShift - Getting Started with the oc command.

I like to think of a machine as OpenShift representation of a Virtual Machine, such as an Amazon Web Services (AWS) EC2 Instance, or a VMWare Virtual Machine, and then a Node, and then the pods running on the node. Machine Configs can be used to configure the Virtual Machine Operating System, such as configuring a Linux systemd service such as sshd or chronyd or Network Manager.

The oc get machineset command can be used to display the desired, current, ready and available machines. The machines will be in the openshift-machine-api namespace. Notice in this example that there are 2 worker machines.

~]$ oc get machineset --namespace openshift-machine-api
NAME                DESIRED   CURRENT   READY   AVAILABLE   AGE
my-cluster-edge     2         2         2       2           140d
my-cluster-infra    3         3         3       3           140d
my-cluster-worker   2         2         2       2           143d

The oc get machines command can be used to display the machines. Notice that the 2 worker machines are listed.

~]$ oc get machines --namespace openshift-machine-api 
NAME                      PHASE     TYPE   REGION   ZONE   AGE
my-cluster-edge-lm6wz     Running                          140d
my-cluster-edge-pmlls     Running                          140d
my-cluster-infra-c4v5h    Running                          140d
my-cluster-infra-mc8rc    Running                          140d
my-cluster-infra-p9cjv    Running                          140d
my-cluster-master-0       Running                          143d
my-cluster-master-1       Running                          143d
my-cluster-master-2       Running                          143d
my-cluster-worker-hsjrp   Running                          140d
my-cluster-worker-v8r9r   Running                          140d

The oc delete machine command can be used to delete a machine. This will also delete the node associated with the machine and all of the pods running on the node will be evicted/terminated and respawned on a different worker node.

~]$ oc delete machine my-cluster-worker-v8r9r --namespace openshift-machine-api
machine.machine.openshift.io "my-cluster-worker-v8r9r" deleted

While the machine is being deleted, the phase of the machine should be Deleting. There should also be a new machine. At first the phase of the new machine should be Provisioned.

~]$ oc get machines -n openshift-machine-api
NAME                               PHASE         TYPE   REGION   ZONE   AGE
my-cluster-edge-78v55              Running                              631d
my-cluster-edge-tk6gm              Running                              631d
my-cluster-infra-7hpsl             Running                              631d
my-cluster-infra-jld8v             Running                              631d
my-cluster-infra-wxjgn             Running                              631d
my-cluster-master-0                Running                              634d
my-cluster-master-1                Running                              634d
my-cluster-master-2                Running                              634d
my-cluster-worker-hsjrp            Running                              634d
my-cluster-worker-v8r9r            Deleting                             140d
my-cluster-worker-sh56r            Provisioned                          57s

This will reduce the CURRENT count to be less than the DESIRED count. 

A new machine should be automatically created to bring the CURRENT/READY/AVAILABLE count up to the DESIRED count.

~]$ oc get machineset --namespace openshift-machine-api
NAME                DESIRED   CURRENT   READY   AVAILABLE   AGE
my-cluster-edge     2         2         2       2           140d
my-cluster-infra    3         3         3       3           140d
my-cluster-worker   2         1         1       1           143d