[Cluster-devel] RFC: generic improvement to fence agents api

[Fabio M. Di Nitto <fdinitto@redhat.com>]

On 3/19/2011 6:14 PM, Digimer wrote:
> On 03/19/2011 02:34 AM, Fabio M. Di Nitto wrote:
>> Hi all,
>>
>> while discussing on linux-cluster the support of the Tripp Lite switched
>> PDU, it occurred to me that we can effectively improve (almost half) the
>> time it takes to perform power fencing of certain devices, when for
>> example, more than one PSU needs to be powered off to complete the action.
>>
>> Node X has 2 PSU.
>>
>> In our current state, the config would look like:
>>
>> <clusternode .....>
>>  <fence>
>>   <method...>
>>    <device name="..." port="1"/>
>>    <device name="..." port="2"/>
>> .....
>>
>> it means effectively spawning, most likely the same agent, twice.
>> Increasing the time it takes to fence and maybe increasing the
>> possibility to fail to fence if the second connection fails.
>>
>> My suggestion would be to allow to specify a list of ports instead.
>>
>> <clusternode .....>
>>  <fence>
>>   <method...>
>>    <device name="..." ports="1 2"/>
>> ....
>>
>> Either by using a new keyword "ports" or re-using "port" itself. If
>> using "port", current configuration will continue to work as-is and the
>> change effectively would not introduce any backward compatibility issue.
>>
>> This way the agent can:
>>
>> 1) connect once (reducing in most cases the ssh/telnet/whatever time)
>> 2) issue the OFF command as fast as possible (almost in parallel)
>> 3) then wait for the results.
>>
>> By adopting a list, the configuration would look cleaner too IMHO.
>>
>> A quick glance, the change should not affect fenced (David can you
>> confirm please?), and most agents could handle it via the fencing python
>> lib (Marek?).
>>
>> Does it sound reasonable?
>>
>> Cheers
>> Fabio
> 
> I like this idea, but would like to suggest:
> 
> * Keep 'port' for a single port, as it is, and add 'ports' for multiple
> port definitions.
> * When using ports, I'd recommend comma-separated values and
> dash-separated ranges (ie: ports="1,2", ports="1-4", ports="1,3-5") and
> combinations there-of. This strikes me as more "standard" and possibly
> less prone to typos.
> 

The only thing I have against "," or "-" is that they might be easily
part of a port name already.

Range doesn?t make sense to me and it?s complex to interpret/implement.
How many machines have you seen around with so many PSU?s anyway that
need a range to avoid headache? (leaving aside E10K or s390 ;)).

Fabio