[ClusterLabs] Antw: Re: Antw: [EXT] Re: Order set troubles

[Ulrich Windl]

>>> Andrei Borzenkov <arvidjaar at gmail.com> schrieb am 26.03.2021 um 06:19 in
Nachricht <534274b3-a6de-5fac-0ae4-d02c305f1a3f at gmail.com>:
> On 25.03.2021 21:45, Reid Wahl wrote:
>> FWIW we have this KB article (I seem to remember Strahil is a Red Hat
>> customer):
>>   - How do I configure SAP HANA Scale-Up System Replication in a Pacemaker
>> cluster when the HANA filesystems are on NFS shares?(
>> https://access.redhat.com/solutions/5156571)
>> 
> 
> "How do I make the cluster resources recover when one node loses access
> to the NFS server?"
> 
> If node loses access to NFS server then monitor operations for resources
> that depend on NFS availability will fail or timeout and pacemaker will
> recover (likely by rebooting this node). That's how similar
> configurations have been handled for the past 20 years in other HA
> managers. I am genuinely interested, have you encountered the case where
> it was not enough?

That's a big problem with the SAP design (basically it's just too complex).
In the past I had written a kind of resource agent that worked without that
overly complex overhead, but since those days SAP has added much more
complexity.
If the NFS server is external, pacemaker could fence your nodes when the NFS
server is down as first the monitor operation will fail (hanging on NFS), the
the recover (stop/start) will fail (also hanging on NFS). Even when fencing the
node it would not help (resources cannot start) if the NFS server is still
down. So you may end up with all your nodes being fenced and the fail counts
disabling any automatic resource restart.

> 
>> I can't remember if there was some valid reason why we had to use an
>> attribute resource, or if we simply didn't think about the
sequential=false
>> require-all=false constraint set approach when planning this out.
>> 
> 
> Because as I already replied, this has different semantic - it will
> start HANA on both nodes if NFS comes up on any one node.
> 
> But thank you for the pointer, it demonstrates really interesting
> technique. It also confirms that pacemaker does not have native means to
> express such ordering dependency/constraints. May be it should.
> 
>> On Thu, Mar 25, 2021 at 3:39 AM Strahil Nikolov <hunter86_bg at yahoo.com>
>> wrote:
>> 
>>> OCF_CHECK_LEVEL 20
>>> NFS sometimes fails to start (systemd racing condition with dnsmasq)
>>>
>>> Best Regards,
>>> Strahil Nikolov
>>>
>>> On Thu, Mar 25, 2021 at 12:18, Andrei Borzenkov
>>> <arvidjaar at gmail.com> wrote:
>>> On Thu, Mar 25, 2021 at 10:31 AM Strahil Nikolov <hunter86_bg at yahoo.com>
>>> wrote:
>>>>
>>>> Use Case:
>>>>
>>>> nfsA is shared filesystem for HANA running in site A
>>>> nfsB is shared filesystem for HANA running  in site B
>>>>
>>>> clusterized resource of type SAPHanaTopology must run on all systems if
>>> the FS for the HANA is running
>>>>
>>>
>>> And the reason you put NFS under pacemaker control in the first place?
>>> It is not going to switch over, just put it in /etc/fstab.
>>>
>>>> Yet, if siteA dies for some reason, I want to make SAPHanaTopology to
>>> still start on the nodes in site B.
>>>>
>>>> I think that it's a valid use case.
>>>>
>>>> Best Regards,
>>>> Strahil Nikolov
>>>>
>>>> On Thu, Mar 25, 2021 at 8:59, Ulrich Windl
>>>> <Ulrich.Windl at rz.uni-regensburg.de> wrote:
>>>>>>> Ken Gaillot <kgaillot at redhat.com> schrieb am 24.03.2021 um 18:56 in
>>>> Nachricht
>>>> <5bffded9c6e614919981dcc7d0b2903220bae19d.camel at redhat.com>:
>>>>> On Wed, 2021‑03‑24 at 09:27 +0000, Strahil Nikolov wrote:
>>>>>> Hello All,
>>>>>>
>>>>>> I have a trouble creating an order set .
>>>>>> The end goal is to create a 2 node cluster where nodeA will mount
>>>>>> nfsA , while nodeB will mount nfsB.On top of that a depended cloned
>>>>>> resource should start on the node only if nfsA or nfsB has started
>>>>>> locally.
>>>>
>>>> This looks like ad odd design to me, and I wonder: What is the use case?
>>>> (We are using "NFS loop-mounts" for many years, where the cluster needs
>>> the
>>>> NFS service it provides, but that's a different design)
>>>>
>>>> Regards,
>>>> Ulrich
>>>>
>>>>
>>>>
>>>>>>
>>>>>> A prototype code would be something like:
>>>>>> pcs constraint order start (nfsA or nfsB) then start resource‑clone
>>>>>>
>>>>>> I tried to create a set like this, but it works only on nodeB:
>>>>>> pcs constraint order set nfsA nfsB resource‑clone
>>>>>>
>>>>>> Any idea how to implement that order constraint ?
>>>>>> Thanks in advance.
>>>>>>
>>>>>> Best Regards,
>>>>>> Strahil Nikolov
>>>>>
>>>>> Basically you want two sets, one with nfsA and nfsB with no ordering
>>>>> between them, and a second set with just resource‑clone, ordered after
>>>>> the first set.
>>>>>
>>>>> I believe the pcs syntax is:
>>>>>
>>>>> pcs constraint order set nfsA nfsB sequential=false require‑all=false
>>>>> set resource‑clone
>>>>>
>>>>> sequential=false says nfsA and nfsB have no ordering between them, and
>>>>> require‑all=false says that resource‑clone only needs one of them.
>>>>>
>>>>> (I don't remember for sure the order of the sets in the command, i.e.
>>>>> whether it's the primary set first or the dependent set first, but I
>>>>> think that's right.)
>>>>> ‑‑
>>>>> Ken Gaillot <kgaillot at redhat.com 
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Manage your subscription:
>>>>> https://lists.clusterlabs.org/mailman/listinfo/users 
>>>>>
>>>>> ClusterLabs home: https://www.clusterlabs.org/ 
>>>
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> Manage your subscription:
>>>> https://lists.clusterlabs.org/mailman/listinfo/users 
>>>>
>>>> ClusterLabs home: https://www.clusterlabs.org/ 
>>>>
>>>> _______________________________________________
>>>> Manage your subscription:
>>>> https://lists.clusterlabs.org/mailman/listinfo/users 
>>>>
>>>> ClusterLabs home: https://www.clusterlabs.org/ 
>>>
>>> _______________________________________________
>>> Manage your subscription:
>>> https://lists.clusterlabs.org/mailman/listinfo/users 
>>>
>>> ClusterLabs home: https://www.clusterlabs.org/ 
>>>
>> 
>> 
> 
> _______________________________________________
> Manage your subscription:
> https://lists.clusterlabs.org/mailman/listinfo/users 
> 
> ClusterLabs home: https://www.clusterlabs.org/