[Linux-cluster] Writing new fencing agent

[Marek 'marx' Grac]

Hi,

Jonathan Buzzard wrote:
> All good so far. However I am not sure what the requirements of a
> fencing agent are. 

> Can I rename my program fence_aol2 fiddle with cluster.conf and it will work? 

You have to set 'agent' option:
<fencedevice name="apc" agent="fence_apc" ipaddr="1.1.1.1" login="apc" 
passwd="apc"/>

These options will be set to fencing agent on STDIN. Also there is a set 
of getopt arguments (look at existing code).

> Does the fencing agent have to return specific exit codes? 
You should return 0 when operation was finished succesfully.

> Should the fencing agent do something to test the magic packet of death worked or is simply sending it enough? 
All 'standard' fencing agents when rebooting are doing these actions:
1) power off
2) test if the plug/machine is powered off [sometimes it take few seconds]
3) power on

> Does the
> fencing agent need to be able to turn nodes on (I could use Wake On Lan
> for this) as well as off?
>
>   
yes, it should.

> Finally once I have a working and debugged AOL2 fencing agent, how does
> one go about submitting for inclusion in cluster suite. Alternatively if
> this is not wanted (Alert on Lan is a historical protocol and superseded
> by IPMI) what is the best way of pointing other users to it's existance?
>
>   
You can take a look at new fencing agents (available in git / master 
branch). They use a python module for common fencing tasks and it should 
not be a problem to write a new fencing agent (agent for APC devices has 
3kB).  If you will find any problem with new agents don't hesitate and 
contact me.

Marek Grac

-- 
Marek Grac
Red Hat Czech s.r.o.