[ClusterLabs] Antw: [EXT] Colocation per site ?

Tue Mar 30 03:06:22 EDT 2021

You can try the following and see if it works, replacing the items in angle
brackets (<>).

    # pcs constraint colocation add <IPaddr2_rsc> with Master
<SAPHanaController_rsc> INFINITY node-attribute=hana_<sid>_site

However, `pcs constraint colocation add --help` gives no information about
what options it accepts. It just says "[options]".

Usage: pcs constraint [constraints]...
    colocation add [<role>] <source resource id> with [<role>]
                   <target resource id> [score] [options] [id=constraint-id]
        Request <source resource> to run on the same node where pacemaker
has
        determined <target resource> should run.  Positive values of score
        mean the resources should be run on the same node, negative values
        mean the resources should not be run on the same node.  Specifying
        'INFINITY' (or '-INFINITY') for the score forces <source resource>
to
        run (or not run) with <target resource> (score defaults to
"INFINITY").
        A role can be: 'Master', 'Slave', 'Started', 'Stopped' (if no role
is
        specified, it defaults to 'Started').

So it's entirely possible that pcs doesn't support creating colocation
constraints with node attributes. If not, then you could edit the CIB
manually and add a constraint like this:

    <rsc_colocation id="colocate" rsc="<IPaddr2_rsc>"
with-rsc="<SAPHanaController_rsc>" score="INFINITY" with-rsc-role="Master"
node-attribute="hana_<sid>_site"/>

On Mon, Mar 29, 2021 at 9:07 PM Strahil Nikolov <hunter86_bg at yahoo.com>
wrote:

> Hi Ken, can you provide a prototype code example.
>
> Currently,I'm making a script that will be used in a systemd service
> managed by the cluster.
> Yet, I would like to avoid non-pacemaker solutions.
>
> Best Regards,
> Strahil Nikolov
>
> On Mon, Mar 29, 2021 at 20:12, Ken Gaillot
> <kgaillot at redhat.com> wrote:
> On Sun, 2021-03-28 at 09:20 +0300, Andrei Borzenkov wrote:
> > On 28.03.2021 07:16, Strahil Nikolov wrote:
> > > I didn't mean DC as a designated coordinator, but as a physical
> > > Datecenter location.
> > > Last time I checked, the node attributes for all nodes seemed the
> > > same.I will verify that tomorrow (Monday).
> > >
> >
> > Yes, I was probably mistaken. It is different with scale-out, agent
> > puts
> > information in global property section of CIB.
> >
> > Ideally we'd need expression that says "on node where site attribute
> > is
> > the same as on node where clone master is active" but I guess there
> > is
> > no way to express it in pacemaker.
>
> Yep, colocation by node attribute (combined with colocation with
> promoted role)
>
>
> https://clusterlabs.org/pacemaker/doc/en-US/Pacemaker/2.0/html-single/Pacemaker_Explained/index.html#_colocation_properties
>
>
>
> >
> > I do not see any easy way to implement it without essentially
> > duplicating SAPHanaTopology. There are some attributes that are
> > defined
> > but never set so far, you may try to open service request to
> > implement
> > consistent attribute for all nodes on current primary site.
> >
> > ...
> >
> > Hmm ... agent sets (at least, should set) hana_${SID}_vhost attribute
> > for each node and this attribute must be unique and different between
> > two sites. May be worth to look into it.
> >
> >
> > > Best Regards,Strahil Nikolov
> > >
> > >
> > >  On Fri, Feb 19, 2021 at 16:51, Andrei Borzenkov<
> > > arvidjaar at gmail.com> wrote:  On Fri, Feb 19, 2021 at 2:44 PM
> > > Strahil Nikolov <hunter86_bg at yahoo.com> wrote:
> > > >
> > > >
> > > > > Do you have a fixed relation between node >pairs and VIPs? I.e.
> > > > > must
> > > > > A/D always get VIP1, B/E - VIP2 etc?
> > > >
> > > > I have to verify it again, but generally speaking - yes , VIP1 is
> > > > always on nodeA/D (master), VIP2 on nodeB/E (worker1) , etc.
> > > >
> > > > I guess I can set negative constraints (-inf) -> VIP1 on node B/E
> > > > + nodeC/F, but the stuff with the 'same DC as master' is the
> > > > tricky part.
> > > >
> > >
> > > I am not sure I understand what DC has to do with it. You have two
> > > scale-out SAP HANA instances, one is primary, another is secondary.
> > > If
> > > I understand correctly your requirements, your backup application
> > > needs to contact the primary instance which may failover to another
> > > site. You must be using some resource agent for it, to manage
> > > failover. The only one I am aware of is SAPHanaSR-ScaleOut. It
> > > already
> > > sets different node properties for primary and secondary sites.
> > > Just
> > > use them. If you use something else, just look at what attributes
> > > your
> > > RA sets. Otherwise you will be essentially duplicating your RA
> > > functionality because you will somehow need to find out which site
> > > is
> > > currently primary.
> > >
> > > There is no guarantee that pacemaker DC wil be on the same site as
> > > SAP
> > > HANA primary system.
>
> > >
> > >
> >
> > _______________________________________________
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> >
> --
> Ken Gaillot <kgaillot at redhat.com
> >
>
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>

-- 
Regards,

Reid Wahl, RHCA
Senior Software Maintenance Engineer, Red Hat
CEE - Platform Support Delivery - ClusterHA
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