Le 7/14/12 9:13 PM, Göktürk Gezer a écrit :
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.
Absolutely. RFC 4533 says nothing about how to implement replication nor
how to manage the replication configuration.
I don't know OpenLDAP yet but don't think its the same, right?
It's clearly different, but not that much.
And i
believe we shouldn't let administrators to initiate replication under
ou=config base. It is not standart and it is not wise.
The ida we had was to manage configuration using an Administrative Area.
This is not yet implemented though, so we ended up with managing
replication under ou=config atm.
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.
Whe you setup replication, you tell the local server with which remote
server you want to replicate. Obviously, you don't want to replicate
such localized information. Now, you can still consider that we share a
global configuration between all the servers, in which you just name
each server, with the assoictaed informations (IP, port, etc), and now
you can setup a replication mechanism in which you express each
configration using thoses names. For instance, if you have 3 servers A,
B and C, you may have the shared configuration where A -r> B, B-r> C,
B-r>A. This configuration can be replicated as is on , B and C, because
each server will now which replication is of interest to itself.
- 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.
Not sure.
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.
Unless the server can detect which configuration applies to itself.
Bottom line, there are a very litte set of information a server needs to
keep local :
- its IP address
- its port
- its name
The name will be used to identify the configuration that applies to the
local server.
--
Regards,
Cordialement,
Emmanuel Lécharny
www.iktek.com
