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Re: [Linux-cluster] Writing new fencing agent


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="" 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this is not wanted (Alert on Lan is a historical protocol and superseded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.

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