Re: how to configure multi-master

[Buchan Milne <bgmilne@staff.telkomsa.net>]

Please stay on-list.

On Tuesday 22 July 2008 10:41:18 Liutauras Adomaitis wrote:
> On Tue, Jul 22, 2008 at 10:02 AM, Buchan Milne <bgmilne@staff.telkomsa.net>
>
> wrote:
> > On Monday 21 July 2008 14:48:23 Liutauras Adomaitis wrote:
> > > On Mon, Jul 21, 2008 at 12:49 PM, Buchan Milne <
> >
> > bgmilne@staff.telkomsa.net>
> >
> > > wrote:
> > > > On Sunday 20 July 2008 23:34:03 Liutauras Adomaitis wrote:
> >
> > [...]
> >
> > > > > It shows, that it is adding MirrorMode TRUE. So why?
> > > >
> > > > The configuration directive may have been overloaded when
> > > > multi-master was added (after mirrormode). AFAIK it allows the
> > > > database in question
> >
> > to
> >
> > > > both have a syncrepl directive, yet take updates from a DN besides
> > > > the updatedn (see the description on the slapd.conf man page).
> > >
> > > are you saying, that in multimaster configuration I have to have
> > > updatedn directive to be able to do writes?
> >
> > No. Without mirrormode or multi-master, a slave would only accept updates
> > from
> > the updatedn. In multi-master, the master is also a slave, so it needs to
> > accept updates from any DN, while being configured as a slave (having
> > replication configuration).
>
> Sorry, but still don't get it. As you say node in multimaster configuration
> is master and slave at the same time. As a slave it can accept writes only
> having updatedn directive. Right?
> I'm really sorry if I don't understand, but it seems that "No" contradicts
> other sentences.

No means: your interpretation that it is multimaster requires updatedn to be 
set is incorrect.

> > > In thread "explain diff between multimaster and mirror mode" I found
> > > out, that mirrormode is kind of high availability implementation for
> > > openldap. In my case I want to have multimaster replication, which
> > > could allow me
> >
> > to
> >
> > > do writes to different master servers at a time.
> >
> > You may want to think very carefully about why you want this, and not
> > mirrormode, or a single master.
>
> Yes maybe it is not necessary. I have read some posts saying the same -
> people do multimaster then they really don't need it at all. This is my
> first acquaintance with syncrepl and ldap replication, so I don't really
> know what is best for me. I tried master- slave, but it had some undisired
> side effects,

If you are that unspecific about the issues, we can't comment on your 
decision.

> so I decided to switch to configuration there I could do
> writes on "slaves", and turned those slaves into masters. I didn't know
> about updatedn directive which maybe is suitable for me, but needs to be
> tested.
> I decided not to do mirrormode, because according to Dieter Kluenter:
> "Mirror mode is a sort of backup and standby system. Only
> one ldap server should be visible and available, thus allowing write
> operations, while the second ldap-server is in hot standby position,
> and only available to clients"
> But I need to do writes at both master at the same tme.

You haven't explained why, so we can't give you feedback on your decision to 
use multimaster.

> >  Are you sure it is not some other aspect of your configuration? Have you
> > posted details? Have you posted the error message?
>
> The most probably it is my configuration and I'm missing something.
> The error is "shadow context; no update referral at ...", I have posted in
> my first letter. I receive this error on any master I try to do writes. If
> add mirrormode true to the end - I can do writes.

Exactly. Enabling "mirrormode" is a prerequisite for multimaster.

The difference between mirrormode an multimaster (as far as I know) these days 
(post 2.4.6) is really your architecture (whether you allow writes to one 
master, or more), not the configuration (though more than two syncrepl 
statements does mean that it can't be mirrormode).

> I have one central master, and other master are replicated from this one.

This is not the definition of multimaster. As far as I know, the recommended 
architecture for multimaster is that all masters can see (replicate from) each 
other. Otherwise, they are locally writable slaves, with no guarantee of 
convergence.

> Configuration of other masters are the same, except serverID are 2 and 3
> respectively and they have only one syncrepl directive pointing to central
> master. So there is no replication between master002 and master 001.


Regards,
Buchan