[Pacemaker] Help with colocation and order of primitives

[Andrew Martin]

Hi Jake, 


Thanks, that helps to clarify how to properly create the colocation and order constraints and how the crm shell corresponds to the XML. You mentioned that I should "verify the statement didn't create a resource set and change the outcome a little" - can you elaborate on this a bit more? After I re-created the contraints, the XML lists two resource sets in each constraint: 

<constraints> 
<rsc_order id="o_drbd-fs-vm" score="INFINITY"> 
<resource_set action="promote" id="o_drbd-fs-vm-0"> 
<resource_ref id="ms_drbd_r0"/> 
<resource_ref id="ms_drbd_r1"/> 
<resource_ref id="ms_drbd_r2"/> 
</resource_set> 
<resource_set action="start" id="o_drbd-fs-vm-1"> 
<resource_ref id="p_fs_r0"/> 
<resource_ref id="p_virtualdomain_vm0"/> 
</resource_set> 
</rsc_order> 
<rsc_colocation id="c_drbd_libvirt_vm" score="INFINITY"> 
<resource_set id="c_drbd_libvirt_vm-0" role="Master"> 
<resource_ref id="ms_drbd_r0"/> 
<resource_ref id="ms_drbd_r1"/> 
<resource_ref id="ms_drbd_r2"/> 
</resource_set> 
<resource_set id="c_drbd_libvirt_vm-1"> 
<resource_ref id="p_fs_r0"/> 
<resource_ref id="p_virtualdomain_vm0"/> 
</resource_set> 
</rsc_colocation> 
</constraints> 


Is this the desired behavior, or will having two resource sets cause the resources to not start linearly/in order as desired? 


Thanks, 


Andrew 
----- Original Message -----

From: "Jake Smith" <jsmith at argotec.com> 
To: "The Pacemaker cluster resource manager" <pacemaker at oss.clusterlabs.org> 
Sent: Friday, February 10, 2012 12:06:15 PM 
Subject: Re: [Pacemaker] Help with colocation and order of primitives 


----- Original Message ----- 

> From: "Andrew Martin" <amartin at xes-inc.com> 
> To: "The Pacemaker cluster resource manager" 
> <pacemaker at oss.clusterlabs.org> 
> Sent: Friday, February 10, 2012 10:33:44 AM 
> Subject: [Pacemaker] Help with colocation and order of primitives 

> Hello, 

> I am working on configuring a 2-node cluster with 3 DRBD devices, 
> their corresponding filesystem mounts, and a VirtualDomain resource 
> agent. I want to add the appropriate constraints to pacemaker so 
> that these resources only start together on the same node, and that 
> they start in the proper order. I have added the DRBD devices to a 
> Master/Slave object, as outlined in 
> http://www.linbit.com/fileadmin/tech-guides/ha-nfs.pdf . I would 
> like them to start in the following order (and stop in the reverse 
> order): 
> ms_drbd_r0 
> ms_drbd_r1 
> ms_drbd_r2 
> p_filesystem_r0 
> p_filesystem_r1 
> p_filesystem_r2 
> p_virtualdomain_vm0 

> I added the 3 filesystem primitives to a group, g_filesystems, which 
> simplifies this somewhat. Are primitives in a group started in the 
> order they are listed in a group, and stopped in the opposite order? 

Yes and colocated in reverse... 

group test A B C 
order is A B C 
colocation is C B A 
Starts A then B then C, Stops C, B, A. 

> I read through the Pacemaker Explained documentation on colocation 
> and order, 
> http://www.clusterlabs.org/doc/en-US/Pacemaker/1.1/html/Pacemaker_Explained/s-resource-sets-ordering.html 

It shows XML but when adding via the CRM CLI the rules work the same. The CRM CLI is just a(n easier) front-end for the XML (config is still written in XML) 
Guide for CRM CLI is here: 
http://www.clusterlabs.org/doc/crm_cli.html 

> however it seems to mostly address the XML and not how to add 
> constraints via the crm console (crm configure). It seems that I 
> cannot add the Master/Slave objects to a group, so I will need to 
> specify each of them individual in the constraints. Is it possible 
> to include more than 2 resources to a constraint, e.g. 
> colocation c_all_on_one inf: ms_drbd_r0:Master ms_drbd_r1:Master 
> ms_drbd_r2:Master g_filesystems p_virtualdomain_vm0 

Yes you can put more than one primitive in a colocation or order constraint - just be careful when adding multiples of different types of resource. You may want to do "crm configure show xml" to verify the statement didn't create a resource set and change the outcome a little. 
Also with order statements make sure you specify the action when combining different types otherwise the first action will apply to all resources i.e. ms_drbd_r0:promote g_filesystems:start 

> Or, can a single colocation or order constraint only contain 2 
> resources? If so would I need to chain several constraints together, 
> like this: 
> colocation c_r0-r1 inf: ms_drbd_r0:Master ms_drbd_r1:Master 
> colocation c_r1-r2 inf: ms_drbd_r1:Master ms_drbd:r2:Master 
> colocation c_r2-fs inf: ms_drbd_r2:Master g_filesystems 
> colocation c_fs_vm0 inf: g_filesystems p_virtualdomain_vm0 

> Which syntax is supported and how can I achieve these colocation and 
> order constraints? 

> Thanks, 

> Andrew 
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