Re: Enforce serverID 0 is for single-master only

[Rein Tollevik <rein@OpenLDAP.org>]

Howard Chu wrote:
> Rein Tollevik wrote:

> > This would mean that slapd would refuse to start if syncrepl or syncprov
> > finds a contextCSN value with SID=0 in the database upon startup and
> > there is more than one contextCSN, or if MirrorMode is enabled. Syncrepl
> > should refuse to receive updates to contextCSN values under the same
> > conditions, and tear down the connection (and retry later) if one is 
> > seen.
>
> The above check is going to be pretty annoying since there's no 
> convenient offline tool to correct the situation. Note that the tool 
> interface now provides a modify entry point, which is used by slapadd to 
> update the contextCSN. If we provide a slapmodify offline tool, then 
> this might be acceptable, but I still think it's going to be pretty 
> annoying.

Yes, it will be annoying for those that have it misconfigured.  That's 
why I suggest the slapd -c sid=xxx change to allow them easy access to 
fix their mistakes.  But, being informed of a config error instead of 
having to track down the effects of it might not be so bad after all.

> Just from a simple usage perspective, aside from adding a serverID to my 
> config, I shouldn't have to do anything special to convert an existing 
> single-master DB to a MM deployment.

You must also get rid of your old contextCSN with sid=0.  Or you will be 
stuck with a value that no-one updates, and all the refresh phases will 
replay everthing that have happend since you switch to MM..

> > Syncprov should also refuse slapd to start if serverID is 0 and
> > MirrorMode is enabled
>
> That sounds OK.
>
> or any contextCSN with non-zero SIDs are found.
>
> That's probably going too far.

Maybe, but then we will not be enforcing serverID 0 is for single 
master, and cannot assume that a csn with sid=0 was received from a 
mis-configured server.

> > This would require a non-zero serverID also on pure forwarding servers
> > that never changes anything by them self.
>
> I don't think so. If they never change anything then their SID never 
> propagates.

Their sid will not propagate, but the forwarding only servers would 
still barf seeing the serverID 0 it it was enforced as I outlined it.

Rein