[ClusterLabs] Antw: Re: Notification agent and Notification recipients
Ken Gaillot
kgaillot at redhat.com
Tue Aug 8 10:59:15 EDT 2017
On Tue, 2017-08-08 at 17:40 +0530, Sriram wrote:
> 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. ?
Ah, I misunderstood your situation, I thought you had a cloned resource.
For that, the alerts feature (available in Pacemaker 1.1.15 and later)
might be useful:
http://clusterlabs.org/doc/en-US/Pacemaker/1.1-pcs/html-single/Pacemaker_Explained/index.html#idm139900098676896
>
>
> 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.
--
Ken Gaillot <kgaillot at redhat.com>
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