Re: Synchronizing two mirror mode clusters

[Леонид Юрьев <leo@yuriev.ru>]

Sorry, but currently I strongly not recommended multi-master.
We have a big troubles in the same case, but most high load.

I am currently working on the two major issues:
- syncrepl seems unreliable, survives no more than 3-5 min under a
stress test (ITS#7968).
- fix of ITS#7904 does not affect syncrepl, thereby MDB_MAP_FULL may
occur in case of LMDB backed (no ITS now).

But another couple seem be forever:
- replication is significantly slowdown if are more than 3 nodes.
- replication may never be completed until all ldap-write activities
are stopped.

More over, just RTFM http://www.openldap.org/doc/admin24/guide.html
18.2.2.3. Arguments against Multi-Master replication
- If connectivity with a provider is lost because of a network
partition, then "automatic failover" can just compound the problem.
- Typically, a particular machine cannot distinguish between losing
contact with a peer because that peer crashed, or because the network
link has failed.
- If a network is partitioned and multiple clients start writing to
each of the "masters" then reconciliation will be a pain; it may be
best to simply deny writes to the clients that are partitioned from
the single provider.

Leonid.

2014-10-17 20:23 GMT+04:00 Clément OUDOT <clem.oudot@gmail.com>:
> Hi,
>
> I need to set up a backup OpenLDAP cluster and I am looking for advices on
> the best solutions to achieve it.
>
> The situation is:
> * A mirror mode cluster on one geographical site
> * A mirror mode cluster on another geographical site (backup site)
> * I would prefer not to impact configuration of main cluster
> * I think that full multi-master on different geographical site is not the
> best solution (but maybe I am totally wrong on this point)
>
> The backup site must be in sync with the main site.
>
> Here are my two ideas:
> * Configure a syncrepl client to main cluster on each node of the backup
> cluster. Question is: will not be conflicts as each node of the backup
> cluster is already synced with the other backup node?
> * Configure a LDAP proxy (back-ldap) to backup cluster, with syncrepl client
> to main cluster. But would back-ldap be able to write operational attributes
> to backup cluster?
>
>
> I imagine that some of you already have such needs, could you share your
> experience?
>
>
> Thanks,
>
> Clément.
>