[ClusterLabs] Antw: Re: Antw: [EXT] Re: Q: rulke-based operation pause/freeze?

[Ken Gaillot]

On Mon, 2020-03-09 at 11:42 +0100, Ulrich Windl wrote:
> > > > Ken Gaillot <kgaillot at redhat.com> schrieb am 06.03.2020 um
> > > > 16:00 in
> 
> Nachricht
> <bed62f6d2c3d92d09f7306f4108195ccc6f1b99f.camel at redhat.com>:
> > On Fri, 2020‑03‑06 at 08:19 +0100, Ulrich Windl wrote:
> > > > > > Ondrej <ondrej‑clusterlabs at famera.cz> schrieb am 06.03.2020
> > > > > > um
> > > > > > 01:45 in
> > > 
> > > Nachricht
> > > <
> > > 
> 
> 7499_1583455563_5E619D4B_7499_1105_1_2a18c389‑059e‑cf6f‑a840‑
> dec26437fdd1 at famer
> > > .cz>:
> > > > On 3/5/20 9:24 PM, Ulrich Windl wrote:
> > > > > Hi!
> > > > > 
> > > > > I'm wondering whether it's possible to pause/freeze specific
> > > > > resource 
> > > > 
> > > > operations through rules.
> > > > > The idea is something like this: If your monitor operation
> > > > > needes
> > > > > (e.g.) 
> > > > 
> > > > some external NFS server, and thst NFS server is known to be
> > > > down,
> > > > it seems
> > > > better to delay the monitor operation until NFS is up again,
> > > > rather
> > > > than 
> > > > forcing a monitor timeout that will most likely be followed by
> > > > a
> > > > stop 
> > > > operation that will also time out, eventually killing the node
> > > > (which has no
> > > > problem itself).
> > > > > 
> > > > > As I guess it's not possible right now, what would be needed
> > > > > to
> > > > > make this 
> > > > 
> > > > work?
> > > > > In case it's possible, how would an example scenario look
> > > > > like?
> > > > > 
> > > > > Regards,
> > > > > Ulrich
> > > > > 
> > > > 
> > > > Hi Ulrich,
> > > > 
> > > > To determine _when_ this state should be enabled and disabled
> > > > would
> > > > be a 
> > > > different story.
> > > 
> > > For the moment let's assume I know it ;‑) ping‑node, maybe.
> > 
> > I believe that limited scenario is possible, but imperfectly.
> > 
> > You could configure an ocf:pacemaker:ping resource to ping the NFS
> > server IP. Then in the dependent resource, configure the recurring
> > monitor logically like this:
> > 
> >   monitor interval=N
> >      meta attributes
> >         rule when ping attribute lt 1 or not defined
> >         enabled=false
> 
> Assuming my attribute is named "n_up", would the syntax be (sorry,
> I'm not
> fluent with rules):
> "rule when n_up lt1 or not defined"
> 
> From your example it's not quite clear which words are placeholders
> and which
> are reserved words...
> 
> [...]

They're all placeholders :) because the syntax is different in XML, pcs
and crm shell. The XML syntax is described at:

https://clusterlabs.org/pacemaker/doc/en-US/Pacemaker/2.0/html-single/Pacemaker_Explained/index.html#idm47160816617536

In this case, a separate <meta_attributes> block for the operation
would contain something like this:

    <rule id="rule1" score="INFINITY" boolean-op="or">
        <expression id="expr1"
            attribute="n_up" operation="lt" value="1"/>
        <expression id="expr2"
            attribute="n_up" operation="not_defined"/>
    </rule>
    <nvpair id="nvp1" name="enabled" value="false"/>

See the man pages for pcs and crm shell for their equivalent syntax.
(Or maybe someone more familiar can reply with it.)
-- 
Ken Gaillot <kgaillot at redhat.com>