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Rescue an instance
Rescue mode provides a mechanism for access, even if an image renders the instance inaccessible. By default, it starts an instance from the initial image attaching the current boot disk as a secondary one.
Note
Pause, suspend, and stop operations are not allowed when an instance is running in rescue mode, as triggering these actions causes the loss of the original instance state and makes it impossible to unrescue the instance.
As of the 20.0.0 (Train) release rescuing a volume-backed server is not supported.
To perform an instance rescue, use the openstack server rescue command:
$ openstack server rescue SERVERNote
On running the openstack server rescue command, an instance
performs a soft shutdown first. This means that the guest operating
system has a chance to perform a controlled shutdown before the instance
is powered off. The shutdown behavior is configured by the
:oslo.configshutdown_timeout parameter that can be set in the
nova.conf file. Its value stands for the overall period (in
seconds) a guest operating system is allowed to complete the
shutdown.
The timeout value can be overridden on a per image basis by means of
os_shutdown_timeout that is an image metadata setting
allowing different types of operating systems to specify how much time
they need to shut down cleanly.
If you want to rescue an instance with a specific image, rather than
the default one, use the --image parameter:
$ openstack server rescue --image IMAGE_ID SERVERTo restart the instance from the normal boot disk, run the following command:
$ openstack server unrescue SERVER