[ClusterLabs] DRBD on asymmetric-cluster

Jason Voorhees jvoorhees1 at gmail.com
Thu Apr 7 04:29:17 CEST 2016 

Hey guys:

I've been reading a little bit more about rules but there are certain
things that are not so clear to me yet. First, I've created 3 normal
resources and one master/slave resource (clusterdataClone). My
resources and constraints look like this:

# pcs resource
 MTA    (systemd:postfix):      Started nodo1
 Web    (systemd:httpd):        Started nodo1
 IPService      (ocf::heartbeat:IPaddr2):       Started nodo1
 Master/Slave Set: clusterdataClone [clusterdata]
     Masters: [ nodo1 ]
     Slaves: [ nodo2 ]

# pcs constraint show --full
Location Constraints:
  Resource: IPService
    Enabled on: nodo1 (score:10) (id:location-IPService-nodo1-10)
    Enabled on: nodo2 (score:9) (id:location-IPService-nodo2-9)
    Enabled on: nodo1 (score:INFINITY) (role: Started) (id:cli-prefer-IPService)
  Resource: MTA
    Enabled on: nodo1 (score:10) (id:location-MTA-nodo1-10)
    Enabled on: nodo2 (score:9) (id:location-MTA-nodo2-9)
  Resource: Web
    Enabled on: nodo1 (score:10) (id:location-Web-nodo1-10)
    Enabled on: nodo2 (score:9) (id:location-Web-nodo2-9)
  Resource: clusterdataClone
    Constraint: location-clusterdataClone
      Rule: score=INFINITY boolean-op=or  (id:location-clusterdataClone-rule)
        Expression: #uname eq nodo1  (id:location-clusterdataClone-rule-expr)
        Expression: #uname eq nodo2  (id:location-clusterdataClone-rule-expr-1)
Ordering Constraints:
Colocation Constraints:
  Web with IPService (score:INFINITY) (id:colocation-Web-IPService-INFINITY)
  MTA with IPService (score:INFINITY) (id:colocation-MTA-IPService-INFINITY)
  clusterdataClone with IPService (score:INFINITY) (rsc-role:Master)
(with-rsc-role:Started)
(id:colocation-clusterdataClone-IPService-INFINITY)

These are the commands I run to create the master/slave resource and
its contraints:

# pcs cluster cib myfile
# pcs -f myfile resource create clusterdata ocf:linbit:drbd
drbd_resource=clusterdb op monitor interval=30s role=Master op monitor
interval=31s role=Slave
# pcs -f myfile resource master clusterdataClone clusterdata
master-max=1 master-node-max=1 clone-max=2 clone-node-max=1
notify=true
# pcs -f myfile constraint location clusterdataClone rule
score=INFINITY \#uname eq nodo1 or \#uname eq nodo2
# pcs -f myfile constraint colocation add master clusterdataClone with IPService
# pcs cluster cib-push myfile

So now, my master/slave resource is started as Master in the same node
where IPService is already active. So far so good. But the problem is
that I can't move IPService from nodo1 to nodo2. When I run...

# pcs resource move IPService nodo2

it does nothing but... IPService keeps active on nodo1.

Then I tried to remove all my clusterdataClone constraints and repeat
the same commands shows lines above (# pcs -f myfile ...) but this
time without creating a colocation constraint between clusterdataClone
and IPService.  When I do some tests again running...

# pcs resource move IPService nodo2

well, IPService is moved to nodo2, but clusterdataClone keeps active
as Master in node1. I thought it would be promoted as Master in nodo2
and demoted to Slave in nodo1.

Do you know why my master/slave resource is not being "moved as
master" between nodes?

How do I "move" the Master role from nodo1 to nodo2 for
clusterdataClone? I want to make  nodo2 Primary and nodo1 Secondary
but I have no idea how to do this manually (only for testing)

I hope someone can help :(

Thanks in advance

On Mon, Apr 4, 2016 at 4:50 PM, Jason Voorhees <jvoorhees1 at gmail.com> wrote:
> I started reading "Pacemaker explained" but as it's so depth I didn't
> read that section regarding rules yet. I'll take a look at it and test
> it before asking anything again.
>
> Thanks a lot Ken
>
> On Mon, Apr 4, 2016 at 9:26 AM, Ken Gaillot <kgaillot at redhat.com> wrote:
>> On 04/02/2016 01:16 AM, Jason Voorhees wrote:
>>> Hello guys:
>>>
>>> I've been recently reading "Pacemaker - Clusters from scratch" and
>>> working on a CentOS 7 system with pacemaker 1.1.13, corosync-2.3.4 and
>>> drbd84-utils-8.9.5.
>>>
>>> The PDF instructs how to create a DRBD resource that seems to be
>>> automatically started due to a symmetric-cluster setup.
>>>
>>> However I want to setup an asymmetric-cluster/opt-in
>>> (symmetric-cluster=false) but I don't know how to configure a
>>> constraint to prefer node1 over node2 to start my DRBD resource as
>>> Master (Primary).
>>
>> I thought location constraints supported role, but that isn't
>> documented, so I'm not sure. But it is documented with regard to rules,
>> which using pcs might look like:
>>
>> pcs location clusterdataClone rule \
>>   role=master \
>>   score=50 \
>>   '#uname' eq nodo1
>>
>> For a lower-level explanation of rules, see
>> http://clusterlabs.org/doc/en-US/Pacemaker/1.1-pcs/html-single/Pacemaker_Explained/index.html#idm140617356537136
>>
>>> So far this are my resources and constraints:
>>>
>>> [root at nodo1 ~]# pcs resource
>>>  IPService      (ocf::heartbeat:IPaddr2):       Started nodo1
>>>  Web    (systemd:httpd):        Started nodo1
>>>  Master/Slave Set: clusterdataClone [clusterdata]
>>>      Stopped: [ nodo1 nodo2 ]
>>>
>>> [root at nodo1 ~]# pcs constraint
>>> Location Constraints:
>>>   Resource: IPService
>>>     Enabled on: nodo2 (score:50)
>>>     Enabled on: nodo1 (score:100)
>>>   Resource: Web
>>>     Enabled on: nodo2 (score:50)
>>>     Enabled on: nodo1 (score:100)
>>> Ordering Constraints:
>>>   start IPService then start Web (kind:Mandatory)
>>> Colocation Constraints:
>>>   Web with IPService (score:INFINITY)
>>>
>>> My current DRBD status:
>>>
>>> [root at nodo1 ~]# drbdadm role clusterdb
>>> 0: Failure: (127) Device minor not allocated
>>> additional info from kernel:
>>> unknown minor
>>> Command 'drbdsetup-84 role 0' terminated with exit code 10
>>>
>>>
>>> [root at nodo2 ~]# drbdadm role clusterdb
>>> 0: Failure: (127) Device minor not allocated
>>> additional info from kernel:
>>> unknown minor
>>> Command 'drbdsetup-84 role 0' terminated with exit code 10
>>>
>>>
>>> I know that it's possible to configure my cluster as asymmetric and
>>> use constraints to avoid a resource running (or becoming master) on
>>> certain nodes, but this time I would like to learn how to do it with
>>> an opt-in scenario.
>>>
>>> Thanks in advance for your help.
>>>
>>> P.D. nodo1 & nodo2 are spanish names for node1 and node2
>>>
>>> _______________________________________________
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>>>
>>> Project Home: http://www.clusterlabs.org
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>>> Bugs: http://bugs.clusterlabs.org
>>>
>>
>>
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