On 06/06/2013, at 2:27 PM, Vladislav Bogdanov <[email protected]> wrote:
> 05.06.2013 02:04, Andrew Beekhof wrote: >> >> On 05/06/2013, at 5:08 AM, Ferenc Wagner <[email protected]> wrote: >> >>> Dejan Muhamedagic <[email protected]> writes: >>> >>>> On Mon, Jun 03, 2013 at 06:19:06PM +0200, Ferenc Wagner wrote: >>>> >>>>> I've got a script for resource creation, which puts the new resource in >>>>> a shadow CIB together with the necessary constraints, runs a simulation >>>>> and finally offers to commit the shadow CIB into the live config (by >>>>> invoking an interactive crm). This works well. My concern is that if >>>>> somebody else (another cluster administrator) changes anything in the >>>>> cluster configuration between creation of the shadow copy and the >>>>> commit, those changes will be silently reverted (lost) by the commit. >>>>> Is there any way to avoid the possibility of this? According to >>>>> http://article.gmane.org/gmane.linux.highavailability.pacemaker/11021, >>>>> crm provides this functionality for its configure sessions [*], but the >>>>> shadow CIB route has good points as well (easier to script via cibadmin, >>>>> simulation), which I'd like to use. Any ideas? >>>> >>>> Record the two epoch attributes of the cib tag at the beginning >>>> and check if they changed just before applying the changes. >>> >>> Maybe I don't understand you right, but isn't this just narrowing the >>> time window of the race? After all, that concurrent change can happen >>> between the epoch check and the commit, can't it? >> >> The CIB will refuse to accept any update with a "lower" version: >> >> >> http://clusterlabs.org/doc/en-US/Pacemaker/1.1-pcs/html/Pacemaker_Explained/_configuration_version.html > > I recall that LDAP has similar problem, which is easily worked around > with specifying two values, one is original, second is new. > That way you tell LDAP server: > Replace value Y in attribute X to value Z. And if value is not Y at the > moment of modification request, then command fails. "cibadmin --patch" works this way _______________________________________________ Linux-HA mailing list [email protected] http://lists.linux-ha.org/mailman/listinfo/linux-ha See also: http://linux-ha.org/ReportingProblems
