Re: [Xen-users] Debian Etch Xen Cluster (DRBD, GNBD, OCFS2, iSCSI, Heartbeat?)

[Tim Post <echo@xxxxxxxxxxxx>]

On Fri, 2007-09-14 at 11:06 +0200, Christian Horn wrote:
> On Fri, Sep 14, 2007 at 08:37:17AM +0200, Dominik Klein wrote:
> > Christian Horn schrieb:
> > 
> > >Has anyone good ideas on how to prevent domUs that are stored on evms or
> > >clvm from beeing started on multiple dom0s?
> > 
> > You could use a wrapper script for xm.
> > 
> > [...]
> > if ssh $othermachine "xm list $machine"
> > then
> >     echo "domU $machine already running on $othermachine. Exit"
> >     exit 5
> > else
> >     /usr/sbin/xm $*
> > fi
> 

Try SRCE, http://echoreply.us/hg/srce.hg , its a 100% non blocking
cluster interconnect that was designed to do what your doing.

Once installed (make make install make test) see /etc/srced/classes
and /etc/srced/nodes for the simplified cluster config. 

Make sure a link to 'xm' is in /var/srced/exec , then do anything you
want from wherever you want, i.e. 

on node3 xm reboot guest33
on node2 xm migrate --live guest23 someothernode
... or

on all xennodes xm list

'on' is just a wrapper script to control the client, otherwise its

srce -k keyfile.txt -s 1.2.3.4 EXEC "command to run remotely"

There's some documentation to get you going, its very simple. SRCE is
blowfish encrypted and uses characteristics (random) of plain text keys
to authenticate. Its quite safe, tried, tested and tiny, perfect for
dom-0. SSH is such a waste on such things. Under 100k statically linked
with its own encryption and non blocking socket libs. It also has its
own deny/allow tcp wrappers that do not rely on iptables. I've got it in
use on a few hundred machines with no issues.

> Jup, that was one of my thoughts, now that i think more about it it doesnt
> look too fault-proof, especially when more than 2 dom0s are involved in 
> a 'site' of dom0s.
> Maybe some ldap where dom0s lock the domUs in could be nice.
> 
> Btw, from the docs now i have seen that clvm apparently does the locking,
> evms isnt doing this currently (and is also heavier, but the preferred
> solution i.e. when using SLES).

I have :

http://echoreply.us/hg/xmlpulse.hg which gives you a single iteration of
xm-top in XML format which some central place can gather to know what is
where and what its doing. I used libxenstat because it ships with Xen to
keep things simple, you could easily change it to use libvirt or
something else. 

I use SRCE to control stuff like ocfs2 / drbd / aoe and other goodies on
large farms and similar clusters, its really a nice tool. Hopefully you
find it useful and enjoy it :)

You could, also, just use the Xen API .. I made this stuff when such a
thing did not exist. Since we use several virtualization technologies, I
continue to use SRCE to manage them all from one place/method.

Kindly,
--Tim



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