You can create a different machine set to serve a specific purpose in your OKD cluster on oVirt. For example, you might create infrastructure machine sets and related machines so that you can move supporting workloads to the new machines.

This process is not applicable for clusters with manually provisioned machines. You can use the advanced machine management and scaling capabilities only in clusters where the Machine API is operational.

Machine API overview

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

For OKD 4.7 clusters, the Machine API performs all node host provisioning management actions after the cluster installation finishes. Because of this system, OKD 4.7 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 providerSpec 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 machines. Machine sets are to machines as replica sets are to pods. If you need more machines or must scale them down, you change the replicas field on the machine set to meet your compute need.

The following custom resources add more capabilities to your cluster:

Machine autoscaler

The MachineAutoscaler resource automatically scales machines in a cloud. You can set the minimum and maximum scaling boundaries for nodes in a specified machine set, and the machine autoscaler maintains that range of nodes. The MachineAutoscaler object takes effect after a ClusterAutoscaler object exists. Both ClusterAutoscaler and MachineAutoscaler resources are made available by the ClusterAutoscalerOperator object.

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 machine set API. You can set cluster-wide scaling limits for resources such as cores, nodes, memory, GPU, and so on. You can set the priority so that the cluster prioritizes pods so that new nodes are not brought online for less important pods. You can also 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 machine set is scoped to a single zone, so the installation program sends out 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. The autoscaler provides best-effort balancing over the life of a cluster.

Sample YAML for a machine set custom resource on oVirt

This sample YAML defines a 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.

apiVersion: machine.openshift.io/v1beta1
kind: MachineSet
metadata:
  labels:
    machine.openshift.io/cluster-api-cluster: <infrastructure_id> (1)
    machine.openshift.io/cluster-api-machine-role: <role> (2)
    machine.openshift.io/cluster-api-machine-type: <role> (2)
  name: <infrastructure_id>-<role> (3)
  namespace: openshift-machine-api
spec:
  replicas: <number_of_replicas> (4)
  Selector: (5)
    matchLabels:
      machine.openshift.io/cluster-api-cluster: <infrastructure_id> (1)
      machine.openshift.io/cluster-api-machineset: <infrastructure_id>-<role> (3)
  template:
    metadata:
      labels:
        machine.openshift.io/cluster-api-cluster: <infrastructure_id> (1)
        machine.openshift.io/cluster-api-machine-role: <role> (2)
        machine.openshift.io/cluster-api-machine-type: <role> (2)
        machine.openshift.io/cluster-api-machineset: <infrastructure_id>-<role> (3)
    spec:
      metadata:
        labels:
          node-role.kubernetes.io/<role>: "" (2)
      providerSpec:
        value:
          apiVersion: ovirtproviderconfig.machine.openshift.io/v1beta1
          cluster_id: <ovirt_cluster_id> (6)
          template_name: <ovirt_template_name> (7)
          instance_type_id: <instance_type_id> (8)
          cpu: (9)
            sockets: <number_of_sockets> (10)
            cores: <number_of_cores> (11)
            threads: <number_of_threads> (12)
          memory_mb: <memory_size> (13)
          os_disk: (14)
            size_gb: <disk_size> (15)
          network_interfaces: (16)
            vnic_profile_id:  <vnic_profile_id> (17)
          credentialsSecret:
            name: ovirt-credentials (18)
          kind: OvirtMachineProviderSpec
          type: <workload_type> (19)
          userDataSecret:
            name: worker-user-data
1 Specify the infrastructure ID that is based on the cluster ID that you set when you provisioned the cluster. If you have the OpenShift CLI (oc) installed, you can obtain the infrastructure ID by running the following command:
$ oc get -o jsonpath='{.status.infrastructureName}{"\n"}' infrastructure cluster
2 Specify the node label to add.
3 Specify the infrastructure ID and node label. These two strings together cannot be longer than 35 characters.
4 Specify the number of machines to create.
5 Selector for the machines.
6 Specify the UUID for the oVirt cluster to which this VM instance belongs.
7 Specify the oVirt VM template to use to create the machine.
8 Optional: Specify the VM instance type. If you include this parameter, you do not need to specify the hardware parameters of the VM including CPU and memory because this parameter overrides all hardware parameters.
9 Optional: The CPU field contains the CPU’s configuration, including sockets, cores, and threads.
10 Optional: Specify the number of sockets for a VM.
11 Optional: Specify the number of cores per socket.
12 Optional: Specify the number of threads per core.
13 Optional: Specify the size of a VM’s memory in MiB.
14 Optional: Root disk of the node.
15 Optional: Specify the size of the bootable disk in GiB.
16 Optional: List of the network interfaces of the VM. If you include this parameter, OKD discards all network interfaces from the template and creates new ones.
17 Optional: Specify the vNIC profile ID.
18 Specify the name of the secret that holds the oVirt credentials.
19 Optional: Specify the workload type for which the instance is optimized. This value affects the oVirt VM parameter. Supported values: desktop, server (default), high_performance. high_performance improves performance on the VM, but there are limitations. For example, you cannot access the VM with a graphical console. For more information see Configuring High Performance Virtual Machines, Templates, and Pools in the Virtual Machine Management Guide.

Because oVirt uses a template when creating a VM, if you do not specify a value for an optional parameter, oVirt uses the value for that parameter that is specified in the template.

Creating a machine set

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

Prerequisites
  • 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 machine set custom resource (CR) sample and is named <file_name>.yaml.

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

    1. If you are not sure which value to set for a specific field, you can check an existing machine set from your cluster:

      $ oc get machinesets -n openshift-machine-api
      Example output
      NAME                                DESIRED   CURRENT   READY   AVAILABLE   AGE
      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
    2. Check values of a specific 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
              machine.openshift.io/cluster-api-machineset: agl030519-vplxk-worker-us-east-1a
      1 The cluster ID.
      2 A default node label.
  2. Create the new MachineSet CR:

    $ oc create -f <file_name>.yaml
  3. View the list of 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 machine set is available, the DESIRED and CURRENT values match. If the machine set is not available, wait a few minutes and run the command again.