[ClusterLabs] Configure a resource to only run a single instance at all times

[Andrei Borzenkov]

On Wed, Oct 31, 2018 at 3:59 PM jm2109384 at gmail.com <jm2109384 at gmail.com> wrote:
>
> Thanks for responding Andrei.
>
> How would i enable monitors on inactive nodes?

Quoting documentation:

By default, a monitor operation will ensure that the resource is
running where it is supposed to. The
target-role property can be used for further checking.

For example, if a resource has one monitor operation with interval=10
role=Started and a
second monitor operation with interval=11 role=Stopped, the cluster
will run the first monitor on
any nodes it thinks should be running the resource, and the second
monitor on any nodes that it thinks
should not be running the resource (for the truly paranoid, who want
to know when an administrator
manually starts a service by mistake).

> I thought monitors runs on all nodes that the resource is on. Would you be able to provide a configuration sample that i can refer to?
> Or will it be possible to configure the cluster to perform a probe in a given interval? Will appreciate some guidance on this. Thanks
>
>
> On Mon., Oct. 29, 2018, 13:20 Andrei Borzenkov, <arvidjaar at gmail.com> wrote:
>>
>> 29.10.2018 20:04, jm2109384 at gmail.com пишет:
>> > Hi Guys,
>> >
>> > I'm a new user of pacemaker clustering software and I've just configured a
>> > cluster with a single systemd resource. I have the following cluster and
>> > resource configurations below. Failover works perfectly between the two
>> > nodes however, i wanted to have a constraint/rule or a config that will
>> > ensure that my resource has a single instance running on the cluster at all
>> > times. I'd like to avoid the situation where the resource gets started
>> > manually and ends up running on both cluster nodes.  Hoping to get your
>> > advice on how to achieve this. Thanks in advance.
>>
>> pacemaker does one time probe on each node when pacemaker is started.
>> This covers the case when resource was manually started before
>> pacemaker. You can enable monitor on inactive nodes which should also
>> detect if resource was started outside of pacemaker. But note that it
>> leaves you some window (up to monitoring interval) when multiple
>> instances may be up on different nodes until pacemaker is aware of it.
>>
>> >
>> > ----
>> > Cluster Name: cluster1
>> > Corosync Nodes:
>> > node1 node2
>> > Pacemaker Nodes:
>> > node1 node2
>> >
>> > Resources:
>> > Resource: app1_service (class=systemd type=app1-server)
>> >   Operations: monitor interval=10s (app1_service-monitor-interval-10s)
>> >               start interval=0s timeout=120s
>> > (app1_service-start-interval-0s)
>> >               stop interval=0s timeout=120s (app1_service-stop-interval-0s)
>> >               failure interval=0s timeout=120s
>> > (app1_service-failure-interval-0s)
>> >
>> > Stonith Devices:
>> > Fencing Levels:
>> >
>> > Location Constraints:
>> > Ordering Constraints:
>> > Colocation Constraints:
>> > Ticket Constraints:
>> >
>> > Alerts:
>> > No alerts defined
>> >
>> > Resources Defaults:
>> > resource-stickiness: 100
>> > migration-threshold: 1
>> > failure-timeout: 120s
>> > Operations Defaults:
>> > No defaults set
>> >
>> > Cluster Properties:
>> > cluster-infrastructure: corosync
>> > dc-version: 1.1.18-11.el7_5.3-2b07d5c5a9
>> > have-watchdog: false
>> > last-lrm-refresh: 1540829641
>> > no-quorum-policy: ignore
>> > stonith-enabled: false
>> > symmetric-cluster: true
>> >
>> > Quorum:
>> >   Options:
>> >
>> >
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>> >
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>> >
>>
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