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From Göktürk Gezer <gokturk.ge...@gmail.com>
Subject Re: Question about Replication of Config Partition and Schema Partition
Date Sat, 14 Jul 2012 19:13:13 GMT
Hi Devs,

Here i share my findings on LDAP replication in terms of OSGI layer.

   - First of all i found nothing related to replicating configuration of
   LDAP Server on any RFC related to replication. So replicating configuration
   is only ApacheDS's concern because it keeps its configuration as DIT data.
   I don't know OpenLDAP yet but don't think its the same, right? And i
   believe we shouldn't let administrators to initiate replication under
   ou=config base. It is not standart and it is not wise. Simply replicating
   configuration will first break the replication aggreement between servers
   anyway ! You should set some filters on config partition entries to whether
   replicate them, but this would be improper in terms of design IMO.
   - But i'm not against on replicating configuration completely. Some one
   would want to simply clone the server in its entirety. ( This is not
   touched by RFC as i see ) Because our OSGI distribution is Karaf based, we
   can use Karaf Cellar here. Cellar is used to keep multiple Karaf instances
   synched in terms of Bundles,Features, and Configuration.(We can't use its
   configuration aspects because we're keeping our component configurations in
   ApacheDS itself). I quickly looked through its functionality and code. It's
   incomplete but promising. Most importantly it provides API to initiate
   Karaf Instance replication.(Again not complete). So when replication system
   is revisited we can make use of Cellar.
   - I looked at Apache ZooKeeeper a bit, and we should definetely leverage
   it in our LDAP replication system. It is simply a distributed data and
   notification system for clusters. It has strength in node management in
   clusters and good for implementing infrastructure related parts of
   replication system.

So i see no threat to OSGI from LDAP Replication. However i believe
ou=config should be excluded from replication in any scenario. I believe if
we're gonna provide some way to replicate some ApacheDS instance's runtime
layout, we should not do it by LDAP Replication. Because :

   - It is not just config partition manages the server anymore.
   - We just can't be sure that 2 server having the same configuration will
   have same runtime behavior, because they might have different composition
   of bundles.
   - Replicating ou=config is hell of a job because of site specific
   configuration parameters.


Regards,
Gokturk

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