[ClusterLabs] Updated attribute is not displayed in crm_mon

Tue Aug 15 04:42:01 EDT 2017

Hi Ken,

Thanks for the explanation.

As an additional information, we are using Daemon(*1) that registers
Corosync's ring status as attributes, so I want to avoid events where
attributes are not displayed.

*1 It's a ifcheckd that always running, not a resource. and registers
   attributes when Pacemaker is running.
   ( https://github.com/linux-ha-japan/pm_extras/tree/master/tools )
   Attribute example :

   Node Attributes:
   * Node rhel73-1:
       + ringnumber_0                      : 192.168.101.131 is UP
       + ringnumber_1                      : 192.168.102.131 is UP
   * Node rhel73-2:
       + ringnumber_0                      : 192.168.101.132 is UP
       + ringnumber_1                      : 192.168.102.132 is UP

Regards,
Kazunori INOUE

> -----Original Message-----
> From: Ken Gaillot [mailto:kgaillot at redhat.com]
> Sent: Tuesday, August 15, 2017 2:42 AM
> To: Cluster Labs - All topics related to open-source clustering welcomed
> Subject: Re: [ClusterLabs] Updated attribute is not displayed in crm_mon
> 
> On Mon, 2017-08-14 at 12:33 -0500, Ken Gaillot wrote:
> > On Wed, 2017-08-02 at 09:59 +0000, 井上 和徳 wrote:
> > > Hi,
> > >
> > > In Pacemaker-1.1.17, the attribute updated while starting pacemaker is not displayed in crm_mon.
> > > In Pacemaker-1.1.16, it is displayed and results are different.
> > >
> > > https://github.com/ClusterLabs/pacemaker/commit/fe44f400a3116a158ab331a92a49a4ad8937170d
> > > This commit is the cause, but the following result (3.) is expected behavior?
> >
> > This turned out to be an odd one. The sequence of events is:
> >
> > 1. When the node leaves the cluster, the DC (correctly) wipes all its
> > transient attributes from attrd and the CIB.
> >
> > 2. Pacemaker is newly started on the node, and a transient attribute is
> > set before the node joins the cluster.
> >
> > 3. The node joins the cluster, and its transient attributes (including
> > the new value) are sync'ed with the rest of the cluster, in both attrd
> > and the CIB. So far, so good.
> >
> > 4. Because this is the node's first join since its crmd started, its
> > crmd wipes all of its transient attributes again. The idea is that the
> > node may have restarted so quickly that the DC hasn't yet done it (step
> > 1 here), so clear them now to avoid any problems with old values.
> > However, the crmd wipes only the CIB -- not attrd (arguably a bug).
> 
> Whoops, clarification: the node may have restarted so quickly that
> corosync didn't notice it left, so the DC would never have gotten the
> "peer lost" message that triggers wiping its transient attributes.
> 
> I suspect the crmd wipes only the CIB in this case because we assumed
> attrd would be empty at this point -- missing exactly this case where a
> value was set between start-up and first join.
> 
> > 5. With the older pacemaker version, both the joining node and the DC
> > would request a full write-out of all values from attrd. Because step 4
> > only wiped the CIB, this ends up restoring the new value. With the newer
> > pacemaker version, this step is no longer done, so the value winds up
> > staying in attrd but not in CIB (until the next write-out naturally
> > occurs).
> >
> > I don't have a solution yet, but step 4 is clearly the problem (rather
> > than the new code that skips step 5, which is still a good idea
> > performance-wise). I'll keep working on it.
> >
> > > [test case]
> > > 1. Start pacemaker on two nodes at the same time and update the attribute during startup.
> > >    In this case, the attribute is displayed in crm_mon.
> > >
> > >    [root at node1 ~]# ssh -f node1 'systemctl start pacemaker ; attrd_updater -n KEY -U V-1' ; \
> > >                    ssh -f node3 'systemctl start pacemaker ; attrd_updater -n KEY -U V-3'
> > >    [root at node1 ~]# crm_mon -QA1
> > >    Stack: corosync
> > >    Current DC: node3 (version 1.1.17-1.el7-b36b869) - partition with quorum
> > >
> > >    2 nodes configured
> > >    0 resources configured
> > >
> > >    Online: [ node1 node3 ]
> > >
> > >    No active resources
> > >
> > >
> > >    Node Attributes:
> > >    * Node node1:
> > >        + KEY                               : V-1
> > >    * Node node3:
> > >        + KEY                               : V-3
> > >
> > >
> > > 2. Restart pacemaker on node1, and update the attribute during startup.
> > >
> > >    [root at node1 ~]# systemctl stop pacemaker
> > >    [root at node1 ~]# systemctl start pacemaker ; attrd_updater -n KEY -U V-10
> > >
> > >
> > > 3. The attribute is registered in attrd but it is not registered in CIB,
> > >    so the updated attribute is not displayed in crm_mon.
> > >
> > >    [root at node1 ~]# attrd_updater -Q -n KEY -A
> > >    name="KEY" host="node3" value="V-3"
> > >    name="KEY" host="node1" value="V-10"
> > >
> > >    [root at node1 ~]# crm_mon -QA1
> > >    Stack: corosync
> > >    Current DC: node3 (version 1.1.17-1.el7-b36b869) - partition with quorum
> > >
> > >    2 nodes configured
> > >    0 resources configured
> > >
> > >    Online: [ node1 node3 ]
> > >
> > >    No active resources
> > >
> > >
> > >    Node Attributes:
> > >    * Node node1:
> > >    * Node node3:
> > >        + KEY                               : V-3
> > >
> > >
> > > Best Regards
> > >
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> >
> 
> --
> Ken Gaillot <kgaillot at redhat.com>
> 
> 
> 
> 
> 
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