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From "David Bosschaert (JIRA)" <j...@apache.org>
Subject [jira] Updated: (ZOOKEEPER-425) Add OSGi metadata to zookeeper.jar
Date Thu, 19 Nov 2009 14:04:39 GMT

     [ https://issues.apache.org/jira/browse/ZOOKEEPER-425?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

David Bosschaert updated ZOOKEEPER-425:
---------------------------------------

    Attachment: zk_patch3.patch

The attached patch (named zk_patch3.patch) implements some of the functionality. Its not fully
finished yet, I'm attaching it at this point to get some feedback.

The patch:
* Adds the OSGi Metadata to the MANIFEST.MF
* Can be used as just a library bundle if you want to write a zookeeper client in another
OSGi bundle.
* Can be used to run the zookeeper server. To do this the server has to be configured. Configuration
is handled through the OSGi Configuration Admin service. The bundle has an optional dependency
on this service and registers an org.osgi.service.cm.ManagedService service to be configured
by CM. The PID for this service is org.apache.zookeeper and all of the configuration variables
are the same as in the non-OSGi zoo.cfg file (it uses the same ServerConfig class to handle
them). 
All configuration properties have defaults provided, except for the 'clientPort' one, which
has to be provided through Config Admin. For the data directory the OSGi Bundle-private storage
directory is used by default.
* The jar has an OSGi BundleActivator class, which will be triggered if run on an OSGi framework.
* BTW the zookeeper.jar stil also works as a POJ (plain old Jar ;)

note that I updated the ivy.xml file to pull in two OSGi jars that are needed at build time.
However they don't need to be redistributed with the zookeeper jar as they are provided by
the OSGi framework.

There are still a few open questions that I have:
* In OSGi things should really be (re)configurable at runtime. This means that the Configuration
Admin Service may call your ManagedService.updated() callback with changed properties at any
time. I guess the easiest (but not necessarily the most elegant) way to handle this is by
taking down the ZooKeeperServerMain and relaunching it with the modified properties. ZooKeeperServerMain
has a shutdown() method that I could use for this. Would that be the best idea?
* I'm not (yet) familiar with the cluster setup and am wondering whether the configuration
approach that I took also works in that case.
I also intend to provide some unit tests before closing this off.

BTW I haven't gone into detail how the OSGi Configuration Admin service typically works. Let
me know if I need to provide more info on that.

> Add OSGi metadata to zookeeper.jar
> ----------------------------------
>
>                 Key: ZOOKEEPER-425
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-425
>             Project: Zookeeper
>          Issue Type: Improvement
>          Components: build
>    Affects Versions: 3.1.1
>            Reporter: David Bosschaert
>         Attachments: MANIFEST.MF, zk_patch3.patch
>
>
> After adding OSGi metadata to zookeeper.jar it can be used as both an OSGi bundle as
well as an ordinary jar file. 
> In the CXF/DOSGi project the buildsystem does this using the maven-bundle-plugin: http://svn.apache.org/repos/asf/cxf/dosgi/trunk/discovery/distributed/zookeeper-wrapper/pom.xml
> The MANIFEST.MF generated by maven-bundle-plugin is attached to this bug, this works
for the CXF/DOSGi project.
> If your buildsystem isn't using maven, I would advise to use bnd (http://www.aqute.biz/Code/Bnd).
BND defines its own ant task in which you should be able to use more or less the same instructions
as were used in maven:
> <instructions>
>   <Bundle-Name>ZooKeeper bundle</Bundle-Name>
>   <Bundle-Description>This bundle contains the ZooKeeper library</Bundle-Description>
>   <Bundle-SymbolicName>org.apache.hadoop.zookeeper</Bundle-SymbolicName>
>   <Bundle-Version>3.1.1</Bundle-Version>
>   <Import-Package>*</Import-Package>
>   <Export-Package>*;version=3.1.1</Export-Package>
> </instructions>
> Oh and one other thing. Is it really necessary to put the source code in the Jar file
too? I would put that in a separate source distribution :)
> See also: http://mail-archives.apache.org/mod_mbox/hadoop-zookeeper-user/200905.mbox/%3c4A2009B1.3030603@yahoo-inc.com%3e

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