[openstack-dev] [Nova][Ironic] Question about scheduling two instances to same baremetal node

Alex Xu soulxu at gmail.com
Fri Jan 9 08:01:23 UTC 2015

Hi, All

There is bug when running nova with ironic

The case is simple: one baremetal node with 1024MB ram, then boot two
instances with 512MB ram flavor.
Those two instances will be scheduling to same baremetal node.

The problem is at scheduler side the IronicHostManager will consume all the
resources for that node whatever
how much resource the instance used. But at compute node side, the
ResourceTracker won't consume resources
like that, just consume like normal virtual instance. And ResourceTracker
will update the resource usage once the
instance resource claimed, then scheduler will know there are some free
resource on that node, then will try to
schedule other new instance to that node.

I take look at that, there is NumInstanceFilter, it will limit how many
instance can schedule to one host. So can
we just use this filter to finish the goal? The max instance is configured
by option 'max_instances_per_host', we
can make the virt driver to report how many instances it supported. The
ironic driver can just report max_instances_per_host=1.
And libvirt driver can report max_instance_per_host=-1, that means no
limit. And then we can just remove the
IronicHostManager, then make the scheduler side is more simpler. Does make
sense? or there are more trap?

Thanks in advance for any feedback and suggestion.

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