[jen20]

This pattern is a lot safer if you use ZFS. Spot instances don't just disappear though, you get notification and have a chance to perform shutdown actions, except in the case of hardware failure - which is the same with non-spot instances.

[solatic]

- EBS, being block storage, doesn't recognize the filesystem format on top of it, and therefore doesn't recognize if you formatted the block storage as ZFS and therefore will not use ZFS snapshots when using Amazon's native EBS snapshotting. If you wish to use ZFS snapshots, you have to build that on top of what Amazon gives you, along with all the other aspects of ZFS storage, i.e. building a ZFS storage pool from separate EBS volumes. I mean, it would be nice if Amazon had a hosted ZFS solution, but so far, doesn't seem like it.

- Yes, you get a notification, but it's a proprietary notification scheme that your application must be designed to poll for. Why can't Amazon use standard signals like SIGPWR to indicate imminent shutdown?

- Just because it isn't smart for non-spot instances doesn't suddenly make it smart for spot instances ;)

[subway]

SIGPWR is anything but standard, and it's unclear how AWS would even send that signal to your processes without adding an agent to the instance.

Currently they initiate an ACPI shutdown event at the termination time. It's hard to initiate a shutdown in a more standardized manner. An instance shut down via this signal will generally see the init process begin gracefully stopping services, eventually halting on it's own. Typically your init process will get increasingly aggressive with kill signals, as defined by your service definitions, eventually getting to SIGKILL. If your init process fails to get the vcpu halted, after a (undocumented?) period AWS will halt the cpu(s) for you. This is about as graceful a shutdown as you're going to get with 'standard' interfaces.

Termination Notifications go out of their way to give you an extra heads up, in case your application is unlikely to gracefully handle being shut down by the init system. Think DB hosts with a craploads of dirty blocks that take a few minutes to sync to disk at shutdown.