[ClusterLabs] constraining multiple cloned resources to the same node

[Andrei Borzenkov]

On 15.03.2022 21:53, john tillman wrote:
>> On 15.03.2022 19:35, john tillman wrote:
>>> Hello,
>>>
>>> I'm trying to guarantee that all my cloned drbd resources start on the
>>> same node and I can't figure out the syntax of the constraint to do it.
>>>
>>> I could nominate one of the drbd resources as a "leader" and have all
>>> the
>>> others follow it.  But then if something happens to that leader the
>>> others
>>> are without constraint.
>>>
>>
>> Colocation is asymmetric. Resource B is colocated with resource A, so
>> pacemaker decides placement of resource A first. If resource A cannot
>> run anywhere (which is probably what you mean under "something happens
>> to that leader"), resource B cannot run anywhere. This is true also for
>> resources inside resource set.
>>
>> I do not think pacemaker supports "always run these resources together,
>> no matter how many resources can run".
>>

This probably can be emulated by assigning high score less than INFINITY
to colocation constraint.

> 
> 
> Huh, no way to get all the masters to start on the same node.  Interesting.
> 
> The set construct has a boolean field "require-all".  I'll try that before
> I give up.
> 

This applies to constraints external to the set, not to resources inside
the set.

> Could I create a resource (some systemd service) that all the masters are
> colocated with?  Feels like a hack but would it work?
> 

Yes, of course. You could also make colocation based on node attribute
and use some other means to set this attribute.

> Thank you for the response.
> 
> -John
> 
> 
>>> I tried adding them to a group but got a syntax error from pcs saying
>>> that
>>> I wasn't allowed to add cloned resources to a group.
>>>
>>> If anyone is interested, it started from this example:
>>> https://edmondcck.medium.com/setup-a-highly-available-nfs-cluster-with-disk-encryption-using-luks-drbd-corosync-and-pacemaker-a96a5bdffcf8
>>> There's a DRBD partition that gets mounted onto a local directory.  The
>>> local directory is then mounted onto an exported directory (mount
>>> --bind).
>>>  Then the nfs service (samba too) get started and finally the VIP.
>>>
>>> Please note that while I have 3 DRBD resources currently, that number
>>> may
>>> increase after the initial configuration is performed.
>>>
>>> I would just like to know a mechanism to make sure all the DRBD
>>> resources
>>> are colocated.  Any suggestions welcome.
>>>
>>> [root at nas00 ansible]# pcs resource
>>>   * Clone Set: drbdShare-clone [drbdShare] (promotable):
>>>     * Masters: [ nas00 ]
>>>     * Slaves: [ nas01 ]
>>>   * Clone Set: drbdShareRead-clone [drbdShareRead] (promotable):
>>>     * Masters: [ nas00 ]
>>>     * Slaves: [ nas01 ]
>>>   * Clone Set: drbdShareWrite-clone [drbdShareWrite] (promotable):
>>>     * Masters: [ nas00 ]
>>>     * Slaves: [ nas01 ]
>>>   * localShare    (ocf::heartbeat:Filesystem):     Started nas00
>>>   * localShareRead    (ocf::heartbeat:Filesystem):     Started nas00
>>>   * localShareWrite   (ocf::heartbeat:Filesystem):     Started nas00
>>>   * nfsShare      (ocf::heartbeat:Filesystem):     Started nas00
>>>   * nfsShareRead      (ocf::heartbeat:Filesystem):     Started nas00
>>>   * nfsShareWrite     (ocf::heartbeat:Filesystem):     Started nas00
>>>   * nfsService  (systemd:nfs-server):    Started nas00
>>>   * smbService  (systemd:smb):   Started nas00
>>>   * vipN      (ocf::heartbeat:IPaddr2):        Started nas00
>>>
>>> [root at nas00 ansible]# pcs constraint show --all
>>> Location Constraints:
>>> Ordering Constraints:
>>>   promote drbdShare-clone then start localShare (kind:Mandatory)
>>>   promote drbdShareRead-clone then start localShareRead (kind:Mandatory)
>>>   promote drbdShareWrite-clone then start localShareWrite
>>> (kind:Mandatory)
>>>   start localShare then start nfsShare (kind:Mandatory)
>>>   start localShareRead then start nfsShareRead (kind:Mandatory)
>>>   start localShareWrite then start nfsShareWrite (kind:Mandatory)
>>>   start nfsShare then start nfsService (kind:Mandatory)
>>>   start nfsShareRead then start nfsService (kind:Mandatory)
>>>   start nfsShareWrite then start nfsService (kind:Mandatory)
>>>   start nfsService then start smbService (kind:Mandatory)
>>>   start nfsService then start vipN (kind:Mandatory)
>>> Colocation Constraints:
>>>   localShare with drbdShare-clone (score:INFINITY)
>>> (with-rsc-role:Master)
>>>   localShareRead with drbdShareRead-clone (score:INFINITY)
>>> (with-rsc-role:Master)
>>>   localShareWrite with drbdShareWrite-clone (score:INFINITY)
>>> (with-rsc-role:Master)
>>>   nfsShare with localShare (score:INFINITY)
>>>   nfsShareRead with localShareRead (score:INFINITY)
>>>   nfsShareWrite with localShareWrite (score:INFINITY)
>>>   nfsService with nfsShare (score:INFINITY)
>>>   nfsService with nfsShareRead (score:INFINITY)
>>>   nfsService with nfsShareWrite (score:INFINITY)
>>>   smbService with nfsShare (score:INFINITY)
>>>   smbService with nfsShareRead (score:INFINITY)
>>>   smbService with nfsShareWrite (score:INFINITY)
>>>   vipN with nfsService (score:INFINITY)
>>> Ticket Constraints:
>>>
>>> Thank you for your time and attention.
>>>
>>> -John
>>>
>>>
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