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

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

On 3/21/2011 9:40 AM, Marek Grac wrote:
> Hi,
> 
> On 03/19/2011 07:34 AM, Fabio M. Di Nitto wrote:
>>     <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?).
> 
> 1) connect once will work only for connection-based fence agents. It
> won't help with SNMP + HTTP REST and there won't be any benefits for
> drac/ilo/ipmi that can turn off only one machine. Rough estimate is that
> it can help us to improve time in 1/3 to 1/2 fence agents.

Of course, it?s a benefit for a subset of the agents.

> 
> 2) parallelism is possible only on those fence devices that works in
> async mode. Issuing more than one command will also increase a need for
> QE. Some of those devices are not able even to handle 'get status'
> immediately after 'power off' (reason for --power-wait). Serialization
> within same connection is definitely possible and for fencing python lib
> we can implement that directly in library.

Assuming we agree to do it, let?s get it upstream first, then we will
worry about QE at a later stage.

I think starting from serialization within the same connection is
already a good start. The parallelism is not real anyway. I don?t expect
forking of commands as that would lead to other issues, as you already
described.

> 
> -) "ports" is better than "port" because such change will have impact
> also on UI and we have to distinguish if fence agent accept more than
> one port or not.

ACK.

> 
> -) There is no character that can't be used for name of virtual machine.

I don?t think vms are a problem here, since each vm has only one port?

Fabio