[sheepdog] [PATCH v2] sheep: remove master node

[MORITA Kazutaka]

At Thu, 18 Jul 2013 18:37:16 +0800,
Liu Yuan wrote:
> 
> On Thu, Jul 18, 2013 at 06:59:54PM +0900, MORITA Kazutaka wrote:
> > From: MORITA Kazutaka <morita.kazutaka at lab.ntt.co.jp>
> > 
> > The current procedure to handle sheep join is as follows.
> > 
> >  1. The joining node sends a join request.
> >  2. The master node accepts the request.
> >  3. All the nodes update cluster members.
> > 
> > This procedure has some problems:
> > 
> >  - The master election is too complex to maintain.
> >    It is very difficult to make sure that the implementation is
> >    correct.
> > 
> >  - The master node can fail while it is accepting the joining node.
> >    The newly elected master has to take over the process, but it's
> >    usually difficult to implement because we have to know what the
> >    previous master did and what it did not before its failure.
> > 
> > This patch changes the sheep join procedure to the following.
> > 
> >  1. The joining node sends a join request.
> >  2. Some of the existing nodes accept the request.
> >  3. All the nodes update cluster members.
> > 
> > It is allowed for the multiple nodes to call sd_join_handler() against
> > the same join request, but at least one node must have to do it.  With
> > this change, we can eliminate a master, and node failure while
> > accepting node join is also allowed.
> > 
> > Removing a master from zookeeper is not easy since it doesn't expect
> > that multiple nodes send EVENT_ACCEPT.  I'll leave this for another
> > day.
> > 
> > Signed-off-by: MORITA Kazutaka <morita.kazutaka at lab.ntt.co.jp>
> > ---
> >  include/shepherd.h        |    3 --
> >  sheep/cluster.h           |    2 +-
> >  sheep/cluster/corosync.c  |   60 +++--------------------
> >  sheep/cluster/local.c     |   38 +++++++--------
> >  sheep/cluster/shepherd.c  |   43 +++++------------
> >  sheep/cluster/zookeeper.c |   75 ++++++++++++++---------------
> 
> zk code wasn't removed.

Oops, sorry for that.  I'll send an updated version.

Thanks,

Kazutaka