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23 October 2008


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Russell Coker

By "When coupled with hardware predictive failure analysis[3] and smart HA software, outages can sometimes be completely avoided" do you mean having the virtual machine migrate away from hardware that is likely to fail? Is this going to be easy to do? Last time I checked your HA system only supported stopping and starting services, no direct migration.

Alan R.

You understood perfectly.

If you tell Heartbeat that a given resource supports a "migrate" action, it will use that action in preference to stop/start to migrate that resource - if it can.

So, you reserve an attribute for system health that you use in your rules, and monitor system health, and set the attribute accordingly, then, like magic, things migrate away when the health is thought to be bad.

It would be nice to have a built in series of attributes like #health-* and so on that were automatically taken into account for all resources. That would make it even easier.

This is not tied in to any particular virtualization technology, or to virtualization at all. It could be used with checkpoint/restart in an application, for example. It just has to behave like a migrate operation. Our current Xen and OpenVZ resources support it - but it's not magic - if your resource supports it, you can write an RA that supports it, and we will use it- when configured correctly.

Of course, you can't migrate a crashed resource, or migrate away from a dead machine, and there are some sensible dependency restrictions as well. [If a migratable resource depends on a non-migratable, non-clonable resource, then it can't be migrated]

Alan R.

It's worth noting that Pacemaker (a child project of Linux-HA - formerly called the Linux-HA CRM) does implement this convenient type of health monitoring - that applies to every resource on the machine.

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