[Pacemaker] drbd 8.3.2 stacked resources controlled by pacemaker

[Lars Ellenberg]

On Wed, Sep 23, 2009 at 01:30:09AM +0300, Dan Frincu wrote:
> bump
>
> anyone?
>
> Dan Frincu wrote:
>> Hello all,
>>
>> I'm trying to build an architecture that I'm not 100% sure will work  
>> so I need some input on the matter. The design is:
>> - 4 servers (now running on test xen virtual machines)
>> - the servers will be divided in two separate geographical locations,  
>> 2 servers in site A and 2 servers in site B
>> - each pair of servers from the same site will form a cluster
>> - each cluster from both sites will be linked as a stacked resource  
>> (stacked-on-top-of)
>>
>> For this setup I'm using drbd-8.3.2-3.x86_64.rpm,  
>> heartbeat-3.0.0-33.2.x86_64.rpm, openais-0.80.5-15.1.x86_64.rpm,  
>> resource-agents-1.0-31.4.x86_64.rpm and their respective dependencies.
>>
>> One question that popped to my mind was that pacemaker is using  
>> multicast, so the connection between the two sites (if it is done  
>> through the public internet) should involve multicast routing? What  
>> bandwidth requirements should be for this kind of setup? I'm assuming  
>> that the high end requirements will be on the drbd replication part,  
>> but also I'm interested if there are any specific requirements related  
>> to latency, delay and (probably) jitter on the multicast connection as  
>> it uses (correct me if I'm wrong) UDP as a transport?

You could use pacemaker + heartbeat cluster comm.
or you could just do independent clusters,
and have an admin intervene and switch on side "global target role
attribute" to started or some such,
I don't think you really want to fully automate site failover just yet.

>> So far I've configured all 4 virtual machines with drbd, created  
>> "normal" resources, stacked resources and all seems to be in order,  
>> the problem is that I don't know how does pacemaker deal with stacked  
>> resources.

There should be a section in the DRBD users guide by now,
check it out.

Basically you just configure two ocf:linbit:drbd thingies,
and have one depend on the Master role of the other.

>> I mean, the goal here is to have one service, let's say apache, run on  
>> a device on the stacked resource and to be handled by pacemaker so  
>> that the apache server either runs on primary stacked resource on site  
>> A, or fails over on stacked resource on site B, and underneath all  
>> that, if in site A one of the two servers fails, it switches to the  
>> other one and the same should happen in site B.

I'm not sure about the split-site cluster with fully automated
site-failover. I'd go for the "operator interaction required",
half-automated site-failover case,
in which case you do not really need all four nodes in the same
pacemaker cluster anyways.

>> So the question is, how do I get pacemaker to start both normal and  
>> stacked resources, promote normal and stacked resources as primary and  
>> then start a web server on the stacked resource that becomes primary.

proper constraints ;)
Apache -> Filesystem -> drbd-top:Master -> drbd-lower:Master

>> Any relevant documentation links or examples are more than welcome,
>> as  well as ideas and suggestions.

-- 
: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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