[ClusterLabs] Antw: Re: Notification agent and Notification recipients

Tue Aug 8 08:10:59 EDT 2017

Hi Ulrich,

Please see inline.

On Tue, Aug 8, 2017 at 2:01 PM, Ulrich Windl <
Ulrich.Windl at rz.uni-regensburg.de> wrote:

> >>> Sriram <sriram.ec at gmail.com> schrieb am 08.08.2017 um 09:30 in
> Nachricht
> <CAMvdjurcQc6t=ZfGr=cRL25Xq0Je9h9F_TvZXyxVAn3n+Dvcgw at mail.gmail.com>:
> > Hi Ken & Jan,
> >
> > In the cluster we have, there is only one resource running. Its a OPT-IN
> > cluster with resource-stickiness set to INFINITY.
> >
> > Just to clarify my question, lets take a scenario where there are four
> > nodes N1, N2, N3, N4
> > a. N1 comes up first, starts the cluster.
>
> The cluster will start once it has a quorum.
>
> > b. N1 Checks that there is no resource running, so it will add the
> > resource(R) with the some location constraint(lets say score 100)
> > c. So Resource(R) runs in N1 now.
> > d. N2 comes up next, checks that resource(R) is already running in N1, so
> > it will update the location constraint(lets say score 200)
> > e. N3 comes up next, checks that resource(R) is already running in N1, so
> > it will update the location constraint(lets say score 300)
>
> See my remark on quorum above.
>
> Yes you are right, I forgot to mention it.

> f.  N4 comes up next, checks that resource(R) is already running in N1, so
> > it will update the location constraint(lets say score 400)
> > g. For the some reason, if N1 goes down, resource(R) shifts to N4(as its
> > score is higher than anyone).
> >
> > In this case is it possible to notify the nodes N2, N3 that newly elected
> > active node is N4 ?
>
> What type of notification, and what would the node do with it?
> Any node in the cluster always has up to date configuration information.
> So it knows the status of the other nodes also.
>

I agree that the node always has upto date configuration information, but
an application or a thread needs to poll for that information. Is there any
way, where the notifications are received through some action function in
RA. ?

Regards,
Sriram.

>
> >
> > I went through clone notifications and master-slave, Iooks like it either
> > requires identical resources(Anonymous) or Unique or Stateful resources
> to
> > be running
> > in all the nodes of the cluster, where as in our case there is only
> > resource running in the whole cluster.
>
> Maybe the main reason for not having notifications is that if a node fails
> hard, it won't be able to send out much status information to the other
> nodes.
>
> Regards,
> Ulrich
>
> >
> > Regards,
> > Sriram.
> >
> >
> >
> >
> > On Mon, Aug 7, 2017 at 11:28 AM, Sriram <sriram.ec at gmail.com> wrote:
> >
> >>
> >> Thanks Ken, Jan. Will look into the clone notifications.
> >>
> >> Regards,
> >> Sriram.
> >>
> >> On Sat, Aug 5, 2017 at 1:25 AM, Ken Gaillot <kgaillot at redhat.com>
> wrote:
> >>
> >>> On Thu, 2017-08-03 at 12:31 +0530, Sriram wrote:
> >>> >
> >>> > Hi Team,
> >>> >
> >>> >
> >>> > We have a four node cluster (1 active : 3 standby) in our lab for a
> >>> > particular service. If the active node goes down, one of the three
> >>> > standby node  becomes active. Now there will be (1 active :  2
> >>> > standby : 1 offline).
> >>> >
> >>> >
> >>> > Is there any way where this newly elected node sends notification to
> >>> > the remaining 2 standby nodes about its new status ?
> >>>
> >>> Hi Sriram,
> >>>
> >>> This depends on how your service is configured in the cluster.
> >>>
> >>> If you have a clone or master/slave resource, then clone notifications
> >>> is probably what you want (not alerts, which is the path you were going
> >>> down -- alerts are designed to e.g. email a system administrator after
> >>> an important event).
> >>>
> >>> For details about clone notifications, see:
> >>>
> >>> http://clusterlabs.org/doc/en-US/Pacemaker/1.1-pcs/html-sing
> >>> le/Pacemaker_Explained/index.html#_clone_resource_agent_requirements
> >>>
> >>> The RA must support the "notify" action, which will be called when a
> >>> clone instance is started or stopped. See the similar section later for
> >>> master/slave resources for additional information. See the mysql or
> >>> pgsql resource agents for examples of notify implementations.
> >>>
> >>> > I was exploring "notification agent" and "notification recipient"
> >>> > features, but that doesn't seem to work. /etc/sysconfig/notify.sh
> >>> > doesn't get invoked even in the newly elected active node.
> >>>
> >>> Yep, that's something different altogether -- it's only enabled on RHEL
> >>> systems, and solely for backward compatibility with an early
> >>> implementation of the alerts interface. The new alerts interface is
> more
> >>> flexible, but it's not designed to send information between cluster
> >>> nodes -- it's designed to send information to something external to the
> >>> cluster, such as a human, or an SNMP server, or a monitoring system.
> >>>
> >>>
> >>> > Cluster Properties:
> >>> >  cluster-infrastructure: corosync
> >>> >  dc-version: 1.1.17-e2e6cdce80
> >>> >  default-action-timeout: 240
> >>> >  have-watchdog: false
> >>> >  no-quorum-policy: ignore
> >>> >  notification-agent: /etc/sysconfig/notify.sh
> >>> >  notification-recipient: /var/log/notify.log
> >>> >  placement-strategy: balanced
> >>> >  stonith-enabled: false
> >>> >  symmetric-cluster: false
> >>> >
> >>> >
> >>> >
> >>> >
> >>> > I m using the following versions of pacemaker and corosync.
> >>> >
> >>> >
> >>> > /usr/sbin # ./pacemakerd --version
> >>> > Pacemaker 1.1.17
> >>> > Written by Andrew Beekhof
> >>> > /usr/sbin # ./corosync -v
> >>> > Corosync Cluster Engine, version '2.3.5'
> >>> > Copyright (c) 2006-2009 Red Hat, Inc.
> >>> >
> >>> >
> >>> > Can you please suggest if I m doing anything wrong or if there any
> >>> > other mechanisms to achieve this ?
> >>> >
> >>> >
> >>> > Regards,
> >>> > Sriram.
> >>> >
> >>> >
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> >>>
> >>> --
> >>> Ken Gaillot <kgaillot at redhat.com>
> >>>
> >>>
> >>>
> >>>
> >>>
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> >>>
> >>
> >>
>
>
>
>
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