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

[Andrei Borzenkov]

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.

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.
>   
>