[ClusterLabs] constraining multiple cloned resources to the same node

[Andrei Borzenkov]

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".

> 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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