[Linux-cluster] Fencing Driver API Requirements

[Jonathan Buzzard]

On Mon, 2008-04-14 at 20:47 +0200, Marek 'marx' Grac wrote:
> Hi,
> 
> gordan at bobich.net wrote:
> >
> > I remember that this was mentioned several times in the last few 
> > months, but has any documentation been put together on the API that 
> > the fencing drivers are supposed to cover?
> >
> > I'm looking into writing a fencing driver based on disabling switch 
> > ports on a managed 3com switch via the telnet interface, and I'd like 
> > to make sure 
> > that it conforms to any speciffic requirements that might exist. If 
> > someone could point me at the relevant URL, that would be most 
> > appreciated.
> 
> There is a new python module in the git (master branch / 
> cluster/gence/agents/lib/fencing.py) that should contain everything you 
> should need to write a fence agent. This module was used to built 
> several agents (they are just in the git tree) eg. apc/apc.py, 
> drac/drac5.py, wti/wti.py. If you will find any problem with fencing.py, 
> let me know and I will try to fix it.
> 

The issue is that with such a critical component of a cluster (if the
fencing is not right bad things will happen) that in order to write a
new fencing agent one has to start reverse engineering from source to
work out what you need to do.

This is incredibly bad practice, and is bound to lead to improperly
implemented fencing agents that then lead to bad things happening on
clusters with these fencing agents.

There a loads of potential fencing devices out there that could be
supported, that are currently not. From my perspective trying to
implement a fencing agent for Alert On Lan 2, it was easier to reverse
engineer the magic packets of death using tcpdump and IDA pro as well as
implementing a C based Linux command tool to generate them, than it has
been to write a functioning fencing agent.

It would take a couple of hours tops for someone to write a spec for
what a fencing agent needs to do.


JAB.

-- 
Jonathan A. Buzzard                      Tel: +441382-386998
Storage Administrator, College of Life Sciences
University of Dundee, DD1 5EH