05.06.2013 02:04, Andrew Beekhof wrote: > > On 05/06/2013, at 5:08 AM, Ferenc Wagner <wf...@niif.hu> wrote: > >> Dejan Muhamedagic <deja...@fastmail.fm> 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. _______________________________________________ Linux-HA mailing list Linux-HA@lists.linux-ha.org http://lists.linux-ha.org/mailman/listinfo/linux-ha See also: http://linux-ha.org/ReportingProblems
