Reboot annotation

The reboot annotation can be used for rebooting BareMetalHosts in the provisioned state. The annotation key takes either of the following forms:


In its basic form (, the annotation will trigger a reboot of the BareMetalHost. The controller will remove the annotation as soon as it has restored power to the host.

The advanced form ({key}) includes a unique suffix (indicated with {key}). In this form the host will be kept in PoweredOff state until the annotation has been removed. This can be useful if some tasks needs to be performed while the host is in a known stable state. The purpose of the {key} is to allow multiple clients to use the API simultaneously in a safe way. Each client chooses a key and touches only the annotations that has this key to avoid interfering with other clients.

If there are multiple annotations, the controller will wait for all of them to be removed (by the clients) before powering on the host. Similarly, if both forms of annotations are used, the{key} form will take precedence. This ensures that the host stays powered off until all clients are ready (i.e. all annotations are removed).

The annotation value should be a JSON map containing the key mode and a value hard or soft to indicate if a hard or soft reboot should be performed. It is not necessary to specify the annotation value. In case it is omitted, the default is to first try a soft reboot, and if that fails, do a hard reboot.

The exact behavior of hard and soft reboot depends on the Ironic configuration. Please see the Ironic configuration reference for more details on this, e.g. the soft_power_off_timeout variable is relevant.

Here are a few examples of the reboot annotation:

  • - immediate reboot via soft shutdown first, followed by a hard shutdown if the soft shutdown fails.
  • {'mode':'hard'} - immediate reboot via hard shutdown, potentially allowing for high-availability use-cases.
  •{key} - phased reboot, issued and managed by the client registered with the key, via soft shutdown first, followed by a hard reboot if the soft reboot fails.
  •{key}: {'mode':'hard'} - phased reboot, issued and managed by the client registered with the key, via hard shutdown.

And here is a “full” example showing a BareMetalHost with the annotation applied:

kind: BareMetalHost
  name: example
    # The basic form with no value ""
    # Advanced form with value "{'mode':'soft'}"
  online: true
  bootMACAddress: 00:8a:b6:8e:ac:b8
  bootMode: legacy
    address: ipmi://
    credentialsName: example-bmc-secret

Why is this needed?

  • It enables controllers and users to perform reboots.
  • It provides a way to remediate failed hosts. (“Have you tried turning it off and on again?”)
  • It provides a stable state (powered off) where certain tasks can be performed without risk of interference from the powered off machine.


  • Clients using this API must respect each other and clean up after themselves. Otherwise they will step on each others toes by for example, leaving an annotation indefinitely or removing someone else’s annotation before they were ready.

For more details please check the reboot interface proposal.