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You can create a different machine set to serve a specific purpose in your OpenShift Container Platform cluster on Microsoft Azure. 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 OpenShift Container Platform resources.

For OpenShift Container Platform 4.11 clusters, the Machine API performs all node host provisioning management actions after the cluster installation finishes. Because of this system, OpenShift Container Platform 4.11 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.

Control plane machines cannot be managed by machine sets.

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 OpenShift Container Platform 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 OpenShift Container Platform version 3.11, you could not roll out a multi-zone architecture easily because the cluster did not manage machine provisioning. Beginning with OpenShift Container Platform 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. 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.

Sample YAML for a machine set custom resource on Azure

This sample YAML defines a machine set that runs in the 1 Microsoft Azure zone in a region and creates nodes that are labeled with node-role.kubernetes.io/<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>-<region> (3)
  namespace: openshift-machine-api
spec:
  replicas: 1
  selector:
    matchLabels:
      machine.openshift.io/cluster-api-cluster: <infrastructure_id> (1)
      machine.openshift.io/cluster-api-machineset: <infrastructure_id>-<role>-<region> (3)
  template:
    metadata:
      creationTimestamp: null
      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>-<region> (3)
    spec:
      metadata:
        creationTimestamp: null
        labels:
          machine.openshift.io/cluster-api-machineset: <machineset_name> (4)
          node-role.kubernetes.io/<role>: "" (2)
      providerSpec:
        value:
          apiVersion: azureproviderconfig.openshift.io/v1beta1
          credentialsSecret:
            name: azure-cloud-credentials
            namespace: openshift-machine-api
          image: (5)
            offer: ""
            publisher: ""
            resourceID: /resourceGroups/<infrastructure_id>-rg/providers/Microsoft.Compute/images/<infrastructure_id> (6)
            sku: ""
            version: ""
          internalLoadBalancer: ""
          kind: AzureMachineProviderSpec
          location: <region> (7)
          managedIdentity: <infrastructure_id>-identity (1)
          metadata:
            creationTimestamp: null
          natRule: null
          networkResourceGroup: ""
          osDisk:
            diskSizeGB: 128
            managedDisk:
              storageAccountType: Premium_LRS
            osType: Linux
          publicIP: false
          publicLoadBalancer: ""
          resourceGroup: <infrastructure_id>-rg (1)
          sshPrivateKey: ""
          sshPublicKey: ""
          subnet: <infrastructure_id>-<role>-subnet  (1) (2)
          userDataSecret:
            name: worker-user-data (2)
          vmSize: Standard_D4s_v3
          vnet: <infrastructure_id>-vnet (1)
          zone: "1" (8)
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 installed, you can obtain the infrastructure ID by running the following command:
$ oc get -o jsonpath='{.status.infrastructureName}{"\n"}' infrastructure cluster

You can obtain the subnet by running the following command:

$  oc -n openshift-machine-api \
    -o jsonpath='{.spec.template.spec.providerSpec.value.subnet}{"\n"}' \
    get machineset/<infrastructure_id>-worker-centralus1

You can obtain the vnet by running the following command:

$  oc -n openshift-machine-api \
    -o jsonpath='{.spec.template.spec.providerSpec.value.vnet}{"\n"}' \
    get machineset/<infrastructure_id>-worker-centralus1
2 Specify the node label to add.
3 Specify the infrastructure ID, node label, and region.
4 Optional: Specify the machine set name to enable the use of availability sets. This setting only applies to new compute machines.
5 Specify the image details for your machine set. If you want to use an Azure Marketplace image, see "Selecting an Azure Marketplace image".
6 Specify an image that is compatible with your instance type. The Hyper-V generation V2 images created by the installation program have a -gen2 suffix, while V1 images have the same name without the suffix.
7 Specify the region to place machines on.
8 Specify the zone within your region to place machines on. Be sure that your region supports the zone that you specify.

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 OpenShift Container Platform 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.

Selecting an Azure Marketplace image

You can create a machine set running on Azure that deploys machines that use the Azure Marketplace offering. To use this offering, you must first obtain the Azure Marketplace image. When obtaining your image, consider the following:

  • While the images are the same, the Azure Marketplace publisher is different depending on your region. If you are located in North America, specify redhat as the publisher. If you are located in EMEA, specify redhat-limited as the publisher.

  • The offer includes a rh-ocp-worker SKU and a rh-ocp-worker-gen1 SKU. The rh-ocp-worker SKU represents a Hyper-V generation version 2 VM image. The default instance types used in OpenShift Container Platform are version 2 compatible. If you are going to use an instance type that is only version 1 compatible, use the image associated with the rh-ocp-worker-gen1 SKU. The rh-ocp-worker-gen1 SKU represents a Hyper-V version 1 VM image.

Prerequisites
  • You have installed the Azure CLI client (az).

  • Your Azure account is entitled for the offer and you have logged into this account with the Azure CLI client.

Procedure
  1. Display all of the available OpenShift Container Platform images by running one of the following commands:

    • North America:

      $  az vm image list --all --offer rh-ocp-worker --publisher redhat -o table
      Example output
      Offer          Publisher       Sku                 Urn                                                             Version
      -------------  --------------  ------------------  --------------------------------------------------------------  --------------
      rh-ocp-worker  RedHat          rh-ocp-worker       RedHat:rh-ocp-worker:rh-ocpworker:4.8.2021122100               4.8.2021122100
      rh-ocp-worker  RedHat          rh-ocp-worker-gen1  RedHat:rh-ocp-worker:rh-ocp-worker-gen1:4.8.2021122100         4.8.2021122100
    • EMEA:

      $  az vm image list --all --offer rh-ocp-worker --publisher redhat-limited -o table
      Example output
      Offer          Publisher       Sku                 Urn                                                             Version
      -------------  --------------  ------------------  --------------------------------------------------------------  --------------
      rh-ocp-worker  redhat-limited  rh-ocp-worker       redhat-limited:rh-ocp-worker:rh-ocp-worker:4.8.2021122100       4.8.2021122100
      rh-ocp-worker  redhat-limited  rh-ocp-worker-gen1  redhat-limited:rh-ocp-worker:rh-ocp-worker-gen1:4.8.2021122100  4.8.2021122100

    Regardless of the version of OpenShift Container Platform you are installing, the correct version of the Azure Marketplace image to use is 4.8.x. If required, as part of the installation process, your VMs are automatically upgraded.

  2. Inspect the image for your offer by running one of the following commands:

    • North America:

      $ az vm image show --urn redhat:rh-ocp-worker:rh-ocp-worker:<version>
    • EMEA:

      $ az vm image show --urn redhat-limited:rh-ocp-worker:rh-ocp-worker:<version>
  3. Review the terms of the offer by running one of the following commands:

    • North America:

      $ az vm image terms show --urn redhat:rh-ocp-worker:rh-ocp-worker:<version>
    • EMEA:

      $ az vm image terms show --urn redhat-limited:rh-ocp-worker:rh-ocp-worker:<version>
  4. Accept the terms of the offering by running one of the following commands:

    • North America:

      $ az vm image terms accept --urn redhat:rh-ocp-worker:rh-ocp-worker:<version>
    • EMEA:

      $ az vm image terms accept --urn redhat-limited:rh-ocp-worker:rh-ocp-worker:<version>
  5. Record the image details of your offer, specifically the values for publisher, offer, sku, and version.

  6. Add the following parameters to the providerSpec section of your machine set YAML file using the image details for your offer:

    Sample providerSpec image values for Azure Marketplace compute machines
    providerSpec:
      value:
        image:
          offer: rh-ocp-worker
          publisher: redhat
          resourceID: ""
          sku: rh-ocp-worker
          type: MarketplaceWithPlan
          version: 4.8.2021122100

Machine sets that deploy machines as Spot VMs

You can save on costs by creating a machine set running on Azure that deploys machines as non-guaranteed Spot VMs. Spot VMs utilize unused Azure capacity and are less expensive than standard VMs. You can use Spot VMs for workloads that can tolerate interruptions, such as batch or stateless, horizontally scalable workloads.

Azure can terminate a Spot VM at any time. Azure gives a 30-second warning to the user when an interruption occurs. OpenShift Container Platform begins to remove the workloads from the affected instances when Azure issues the termination warning.

Interruptions can occur when using Spot VMs for the following reasons:

  • The instance price exceeds your maximum price

  • The supply of Spot VMs decreases

  • Azure needs capacity back

When Azure terminates an instance, a termination handler running on the Spot VM node deletes the machine resource. To satisfy the machine set replicas quantity, the machine set creates a machine that requests a Spot VM.

Creating Spot VMs by using machine sets

You can launch a Spot VM on Azure by adding spotVMOptions to your machine set YAML file.

Procedure
  • Add the following line under the providerSpec field:

    providerSpec:
      value:
        spotVMOptions: {}

    You can optionally set the spotVMOptions.maxPrice field to limit the cost of the Spot VM. For example you can set maxPrice: '0.98765'. If the maxPrice is set, this value is used as the hourly maximum spot price. If it is not set, the maximum price defaults to -1 and charges up to the standard VM price.

    Azure caps Spot VM prices at the standard price. Azure will not evict an instance due to pricing if the instance is set with the default maxPrice. However, an instance can still be evicted due to capacity restrictions.

It is strongly recommended to use the default standard VM price as the maxPrice value and to not set the maximum price for Spot VMs.

Machine sets that deploy machines on Ephemeral OS disks

You can create a machine set running on Azure that deploys machines on Ephemeral OS disks. Ephemeral OS disks use local VM capacity rather than remote Azure Storage. This configuration therefore incurs no additional cost and provides lower latency for reading, writing, and reimaging.

Additional resources

Creating machines on Ephemeral OS disks by using machine sets

You can launch machines on Ephemeral OS disks on Azure by editing your machine set YAML file.

Prerequisites
  • Have an existing Microsoft Azure cluster.

Procedure
  1. Edit the custom resource (CR) by running the following command:

    $ oc edit machineset <machine-set-name>

    where <machine-set-name> is the machine set that you want to provision machines on Ephemeral OS disks.

  2. Add the following to the providerSpec field:

    providerSpec:
      value:
        ...
        osDisk:
           ...
           diskSettings: (1)
             ephemeralStorageLocation: Local (1)
           cachingType: ReadOnly (1)
           managedDisk:
             storageAccountType: Standard_LRS (2)
           ...
    1 These lines enable the use of Ephemeral OS disks.
    2 Ephemeral OS disks are only supported for VMs or scale set instances that use the Standard LRS storage account type.

    The implementation of Ephemeral OS disk support in OpenShift Container Platform only supports the CacheDisk placement type. Do not change the placement configuration setting.

  3. Create a machine set using the updated configuration:

    $ oc create -f <machine-set-config>.yaml
Verification
  • On the Microsoft Azure portal, review the Overview page for a machine deployed by the machine set, and verify that the Ephemeral OS disk field is set to OS cache placement.

Machine sets that deploy machines with ultra disks as data disks

You can create a machine set running on Azure that deploys machines with ultra disks. Ultra disks are high-performance storage that are intended for use with the most demanding data workloads.

You can also create a persistent volume claim (PVC) that dynamically binds to a storage class backed by Azure ultra disks and mounts them to pods.

Data disks do not support the ability to specify disk throughput or disk IOPS. You can configure these prope