Open Stack

----- Original Message -----
> From: "Phil Day" <philip.day at hp.com>
> To: "OpenStack Development Mailing List (not for usage questions)" <openstack-dev at lists.openstack.org>
> 
> >Nova now can detect host unreachable. But it fails to make out host
> >isolation, host dead and nova compute service down. When host unreachable
> >is reported, users have to find out the exact state by himself and then
> >take the appropriate measure to recover. Therefore we'd like to improve the
> >host detection for nova.
> 
> I guess this depends on the service group driver that you use.  For example
> if you use the DB driver, then there is a thread running on the compute
> manager that periodically updates the "alive" status - which included both a
> liveness check (to the extent that the thread is still running) of the
> compute manager and that it can contact the DB.    If the compute manager is
> using conductor then it also includes implicitly a check that the compute
> manager can talk to MQ (a nice side effect of conductor - as before a node
> could be "Up" because it could talk to the DB but not able to process any
> messages)
> 
> So to me the DB driver kind of already covers "send network heartbeat to the
> central agent and writes timestamp in shared storage periodically" - so
> maybe this is more of a specific ServiceGroup Driver issue rather than a
> generic ServiceGroup change ?
> 
> Phil

This refers to the case where the compute host is completely unreachable. Another interesting case, either using passthrough of an entire NIC or an SRIOV VF, is what happens when the link of one of the ports allocated for passthrough is down. It may not be desirable to disable the host entirely in this case, but certainly the user would not expect instances with flavors request a passed through networking device to be scheduled to get a device with a link that is down. I'd be interested in how a nagios or zabbix based solution to this would be architected.

Somewhat tangentially to the above I believe Balazs has re-architected the spec he had proposed in this area somewhat:

    https://review.openstack.org/#/c/87978/

Thanks,

Steve


> From: Jiangying (Jenny) [mailto:jenny.jiangying at huawei.com]
> Sent: 28 April 2014 13:31
> To: openstack-dev at lists.openstack.org
> Subject: [openstack-dev] [nova][service group]improve host state detection
> 
> Nova now can detect host unreachable. But it fails to make out host
> isolation, host dead and nova compute service down. When host unreachable is
> reported, users have to find out the exact state by himself and then take
> the appropriate measure to recover. Therefore we'd like to improve the host
> detection for nova.
> 
> Currently the service group API factors out the host detection and makes it a
> set of abstract internal APIs with a pluggable backend implementation. The
> backend we designed is as follows:
> 
> A detection central agent is introduced. When a member joins into the service
> group, the member host starts to send network heartbeat to the central agent
> and writes timestamp in shared storage periodically. When the central agent
> stops receiving the network heartbeats from a member, it pings the member
> and checks the storage heartbeat before declaring the host to have failed.
> 
> ----------------------------------------------------------------------------------------------------------------
> network heartbeat|network ping|storage heartbeat| state          | reason
> ------------------------|-----------------|------------------------|---------------------------|------------------------------------------
>         OK       |      -     |        -        | Running             | -
>       Not OK     |   Not OK   |     Not OK      | Dead               |
>       hardware failure/abnormal host shut down
>       Not OK     |     OK     |     Not OK      | Service unreachable|
>       service process crashed
>       Not OK     |   Not OK   |       OK        | Isolated           |
>       network unreachable
> ----------------------------------------------------------------------------------------------------------------
> Based on the state recognition table, nova can discern the exact host state
> and assign the reasons.
> 
> Thoughts?
> 
> Jenny
> 
> 
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-- 
Steve Gordon, RHCE
Product Manager, Red Hat Enterprise Linux OpenStack Platform
Red Hat Canada (Toronto, Ontario)