I see a message in Cloud Manager that Lassie rebooted my Linode. What exactly is Lassie?
I see a message in Cloud Manager that Lassie rebooted my Linode. Could you tell me more about what Lassie is, what Lassie does, and how Lassie works?
Overview of Lassie
Lassie is the name of Linode's shutdown watchdog. It is a utility that runs on all of Linode's hosts and determines whether any of the Linodes running on that host are in an inoperable state. If it finds any Linodes that have crashed or are not responding to the hypervisor, Lassie will initiate a boot of the Linode in order to recover them from an unresponsive state and reduce their downtime.
How Lassie works
Every Linode communicates back to the hypervisor on our virtualization hosts on a regular basis. When this communication is disrupted in certain ways indicative of an unresponsive host, Lassie will take notice and issue a boot of that Linode to minimize downtime for our customers.
Shutdowns initiated from within the Linode
In addition to recovering Linodes that experienced an internal system crash, Lassie also takes action in response to shutdowns and reboots when logged into a Linode. When a customer logs into their Linode and runs a command to power off their Linode, such as
shutdown now, Lassie steps in and instructs that Linode to boot up again.
This behavior occurs because the power state change was not performed through the hypervisor. As a result, Lassie simply notices that the Linode stopped communicating with the hypervisor and issues a hard reboot in an attempt to reestablish this communication.
For that reason, the best way to power off a Linode is by logging into Cloud Manager, navigating to the Linode that you want to power down, clicking the "Running" link in the upper-right corner of the Linode's page, then clicking "Power Off" to power off the Linode. You may also issue a shutdown through the API or the
linode-cli utility. All of these methods will power off the Linode at the hypervisor level, suppressing Lassie from taking action to reboot the Linode.
Lassie is enabled by default on new Linodes for its downtime-reducing capabilities, but it is possible to disable Lassie on a specific Linode through Cloud Manager. Simply navigate to the Linode in question, select the Settings tab, click the "Shutdown Watchdog" category, and click the slider bar so that it reads "Disabled". You should get a confirmation message that the watchdog was successfully disabled.
To re-enable Lassie, simply click this slider again. As with disabling Lassie, you should get a confirmation message that the watchdog was successfully enabled.
Lassie provides a valuable service for reducing a Linode's downtime. Every Linode communicates with their hypervisor regularly as a means of establishing that they are in an operational state. When this communication is broken, either through a system crash or a shutdown command, Lassie will send a boot signal to the Linode to revive the server and minimize its downtime. All Linodes have Lassie enabled by default, but it is possible to disable Lassie or re-enable it for a specific Linode.