[systemd-devel] [IDEA] systemd as basis for HA clusters

Tomasz Torcz tomek at pipebreaker.pl
Thu Jul 25 12:21:20 PDT 2013

On Thu, Jul 25, 2013 at 06:51:21PM +0200, Lennart Poettering wrote:
> On Fri, 19.07.13 21:05, Pablo Nehab Hess (pablo at hess.net.br) wrote:
> > Hi all,
> > 
> > I was wondering how much systemd could add to current high
> > availability cluster setups.
> > 
> > Today systemd is used on HA clusters as just an init replacement.
> > However, there are systemd features that might come in handy and
> > improve the overall performance and even reliability of such clusters:
> > 
> > * watchdog functionality as in
> > <http://0pointer.de/blog/projects/watchdog.html> is the most evident
> > feature;
> > * tcp-based dbus communication could be used to exchange information
> > between cluster members;
> > 
> > Also, I believe systemd functionality could be extended so it would
> > take into consideration other nodes' systemd instances in order to
> > make sure each service is always alive somewhere -- call it "floating
> > units" if you will. :-)
> > 
> > Does this idea even make sense? Is it too "one systemd to rule them all"?
> Well, I don't really know what exactly HA clusters would need. However,
> note that we actually do try to draw the line somewhere where systemd
> ends... I have the suspicion the HA cluster stuff something which could
> make great use of systemd's comprehensive bus interfaces, but I am not
> convinced such a project should sit in systemd itself.

  The RH Cluster suite cares about running services, and restarting services
when they fail.  Just like systemd.  Main difference is that you can select
on which host to run this service.  It could be implemented in some daemon
synchronising state between remote systemd's.
  Every time I use ”clustat” I feel like I'm should be looking at
”systemctl status” listing.  When I enable services using ”clusvcadm -e foo”
I feel like it should be ”systemctl enable foo”.  There's a quite big
overlap between cluster suite and systemctl.

Tomasz Torcz                "Funeral in the morning, IDE hacking
xmpp: zdzichubg at chrome.pl    in the afternoon and evening." - Alan Cox

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