Creating a compute machine set on oVirt

The Machine API is a combination of primary resources that are based on the upstream Cluster API project and custom OKD resources.

For OKD 4.12 clusters, the Machine API performs all node host provisioning management actions after the cluster installation finishes. Because of this system, OKD 4.12 offers an elastic, dynamic provisioning method on top of public or private cloud infrastructure.

The two primary resources are:

Machines

A fundamental unit that describes the host for a node. A machine has a specification, which describes the types of compute nodes that are offered for different cloud platforms. For example, a machine type for a worker node on Amazon Web Services (AWS) might define a specific machine type and required metadata.

Machine sets

MachineSet resources are groups of compute machines. Compute machine sets are to compute machines as replica sets are to pods. If you need more compute machines or must scale them down, you change the replicas field on the MachineSet resource to meet your compute need.

The following custom resources add more capabilities to your cluster:

Machine autoscaler

The MachineAutoscaler resource automatically scales compute machines in a cloud. You can set the minimum and maximum scaling boundaries for nodes in a specified compute machine set, and the machine autoscaler maintains that range of nodes.

Cluster autoscaler

This resource is based on the upstream cluster autoscaler project. In the OKD implementation, it is integrated with the Machine API by extending the compute machine set API. You can use the cluster autoscaler to manage your cluster in the following ways:

• Set cluster-wide scaling limits for resources such as cores, nodes, memory, and GPU

• Set the priority so that the cluster prioritizes pods and new nodes are not brought online for less important pods

• Set the scaling policy so that you can scale up nodes but not scale them down

Machine health check

The MachineHealthCheck resource detects when a machine is unhealthy, deletes it, and, on supported platforms, makes a new machine.

In OKD version 3.11, you could not roll out a multi-zone architecture easily because the cluster did not manage machine provisioning. Beginning with OKD version 4.1, this process is easier. Each compute machine set is scoped to a single zone, so the installation program sends out compute machine sets across availability zones on your behalf. And then because your compute is dynamic, and in the face of a zone failure, you always have a zone for when you must rebalance your machines. In global Azure regions that do not have multiple availability zones, you can use availability sets to ensure high availability. The autoscaler provides best-effort balancing over the life of a cluster.

This sample YAML defines a compute machine set that runs on oVirt and creates nodes that are labeled with node-role.kubernetes.io/<node_role>: "".

In this sample, <infrastructure_id> is the infrastructure ID label that is based on the cluster ID that you set when you provisioned the cluster, and <role> is the node label to add.

In addition to the ones created by the installation program, you can create your own compute machine sets to dynamically manage the machine compute resources for specific workloads of your choice.

• Deploy an OKD cluster.

• Install the OpenShift CLI (oc).

• Log in to oc as a user with cluster-admin permission.

Procedure

1. Create a new YAML file that contains the compute machine set custom resource (CR) sample and is named <file_name>.yaml.

   Ensure that you set the <clusterID> and <role> parameter values.

   1. Check values of a specific compute machine set:

      $ oc get machineset <machineset_name> -n \
           openshift-machine-api -o yaml

      Example output

      ...
      template:
          metadata:
            labels:
              machine.openshift.io/cluster-api-cluster: agl030519-vplxk (1)
              machine.openshift.io/cluster-api-machine-role: worker (2)
              machine.openshift.io/cluster-api-machine-type: worker

2. Create the new MachineSet CR:

3. View the list of compute machine sets:

   $ oc get machineset -n openshift-machine-api

   Example output

   NAME                                DESIRED   CURRENT   READY   AVAILABLE   AGE
   agl030519-vplxk-infra-us-east-1a    1         1         1       1           11m
   agl030519-vplxk-worker-us-east-1a   1         1         1       1           55m
   agl030519-vplxk-worker-us-east-1b   1         1         1       1           55m
   agl030519-vplxk-worker-us-east-1c   1         1         1       1           55m
   agl030519-vplxk-worker-us-east-1d   0         0                             55m
   agl030519-vplxk-worker-us-east-1e   0         0                             55m
   agl030519-vplxk-worker-us-east-1f   0         0                             55m

   When the new compute machine set is available, the and CURRENT values match. If the compute machine set is not available, wait a few minutes and run the command again.