Exposing downward metrics for virtual machines

As an administrator, you can expose a set of host and virtual machine (VM) metrics to a guest VM by enabling the downwardMetrics feature gate and configuring a downward metrics device. You can view these metrics by using the command line or the vm-dump-metrics tool.

Note

On Red Hat Enterprise Linux (RHEL) 9, use the command line to view downward metrics.

The vm-dump-metrics tool is not supported on the Red Hat Enterprise Linux (RHEL) 9 platform.

Enabling or disabling the downward metrics feature gate in a YAML file

To expose downward metrics for a host virtual machine, you can enable the downwardMetrics feature gate by editing a YAML file.

Prerequisites

• You must have administrator privileges to enable the feature gate.
• You have installed the OpenShift CLI (oc).

Procedure

1. Open the HyperConverged custom resource (CR) in your default editor by running the following command:

   $ oc edit hyperconvergeds.v1beta1.hco.kubevirt.io kubevirt-hyperconverged -n openshift-cnv
   

2. Choose to enable or disable the downwardMetrics feature gate as follows:

   • To enable the downwardMetrics feature gate, add and then set spec.featureGates.downwardMetrics to true. For example:

     apiVersion: hco.kubevirt.io/v1beta1
     kind: HyperConverged
     metadata:
       name: kubevirt-hyperconverged
       namespace: openshift-cnv
     spec:
         featureGates:
           downwardMetrics: true
     # ...
     

   • To disable the downwardMetrics feature gate, set spec.featureGates.downwardMetrics to false. For example:

     apiVersion: hco.kubevirt.io/v1beta1
     kind: HyperConverged
     metadata:
       name: kubevirt-hyperconverged
       namespace: openshift-cnv
     spec:
         featureGates:
           downwardMetrics: false
     # ...
     

Enabling or disabling the downward metrics feature gate from the CLI

To expose downward metrics for a host virtual machine, you can enable the downwardMetrics feature gate by using the command line.

Prerequisites

• You must have administrator privileges to enable the feature gate.
• You have installed the OpenShift CLI (oc).

Procedure

• Choose to enable or disable the downwardMetrics feature gate as follows:

  • Enable the downwardMetrics feature gate by running the command shown in the following example:

    $ oc patch hyperconvergeds.v1beta1.hco.kubevirt.io kubevirt-hyperconverged -n openshift-cnv \
      --type json -p '[{"op": "replace", "path": \
      "/spec/featureGates/downwardMetrics", \
      "value": true}]'
    

  • Disable the downwardMetrics feature gate by running the command shown in the following example:

    $ oc patch hyperconvergeds.v1beta1.hco.kubevirt.io kubevirt-hyperconverged -n openshift-cnv \
      --type json -p '[{"op": "replace", "path": \
      "/spec/featureGates/downwardMetrics", \
      "value": false}]'
    

Configuring a downward metrics device

You can enable the capturing of downward metrics for a host VM by creating a configuration file that includes a downwardMetrics device. Adding this device establishes that the metrics are exposed through a virtio-serial port.

Prerequisites

• You must first enable the downwardMetrics feature gate.

Procedure

• Edit or create a YAML file that includes a downwardMetrics device, as shown in the following example:

  apiVersion: kubevirt.io/v1
  kind: VirtualMachine
  metadata:
    name: fedora
    namespace: default
  spec:
    dataVolumeTemplates:
      - metadata:
          name: fedora-volume
        spec:
          sourceRef:
            kind: DataSource
            name: fedora
            namespace: openshift-virtualization-os-images
          storage:
            resources: {}
    instancetype:
      name: u1.medium
    runStrategy: Always
    template:
      metadata:
        labels:
          app.kubernetes.io/name: headless
      spec:
        domain:
          devices:
            downwardMetrics: {}
        subdomain: headless
        volumes:
          - dataVolume:
              name: fedora-volume
            name: rootdisk
          - cloudInitNoCloud:
              userData: |
                #cloud-config
                chpasswd:
                  expire: false
                password: '<password>'
                user: fedora
            name: cloudinitdisk
  

• spec.domain.devices.downwardMetrics defines the downwardMetrics device.

• spec.volumes.cloudInitNoCloud.userdata.password defines the password for the fedora user.

Viewing downward metrics by using the CLI

You can view downward metrics by entering a command from inside a guest virtual machine (VM).

Procedure

• Run the following commands:

  $ sudo sh -c 'printf "GET /metrics/XML\n\n" > /dev/virtio-ports/org.github.vhostmd.1'
  

  $ sudo cat /dev/virtio-ports/org.github.vhostmd.1
  

Viewing downward metrics by using the vm-dump-metrics tool

To view downward metrics, install the vm-dump-metrics tool and then use the tool to expose the metrics results.

Note

On Red Hat Enterprise Linux (RHEL) 9, use the command line to view downward metrics. The vm-dump-metrics tool is not supported on the Red Hat Enterprise Linux (RHEL) 9 platform.

Procedure

1. Install the vm-dump-metrics tool by running the following command:

   $ sudo dnf install -y vm-dump-metrics
   

2. Retrieve the metrics results by running the following command:

   $ sudo vm-dump-metrics
   

   Example output:

   <metrics>
     <metric type="string" context="host">
       <name>HostName</name>
       <value>node01</value>
   [...]
     <metric type="int64" context="host" unit="s">
       <name>Time</name>
       <value>1619008605</value>
     </metric>
     <metric type="string" context="host">
       <name>VirtualizationVendor</name>
       <value>kubevirt.io</value>
     </metric>
   </metrics>
   

Additional resources

• Viewing downward metrics by using the command line