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https://issues.apache.org/jira/browse/SLING-2827?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Carsten Ziegeler resolved SLING-2827.
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Resolution: Fixed
I think we have a working implementation now, therefore we can close this
> discovery.impl: a resource based implementation of the discovery.api
> --------------------------------------------------------------------
>
> Key: SLING-2827
> URL: https://issues.apache.org/jira/browse/SLING-2827
> Project: Sling
> Issue Type: New Feature
> Components: Extensions
> Reporter: Stefan Egli
> Assignee: Carsten Ziegeler
> Attachments: discovery.impl.activate_and_changing.patch,
> discovery.impl.bootstrap.patch,
> discovery.impl.loops.timeouts.webconsole.patch, discovery.impl.svn.patch,
> discovery.impl.tar.gz
>
>
> This ticket is about contributing a resource based implementation of the
> discovery api (see [0]) named discovery.impl to Sling. The implementation is
> attached as a .tar.gz - its md5 hash is d8891e5401114b2a629d3ff01044a1d6
> Short description of the discovery.impl:
> The discovery.impl is an out-of-the-box implementation of the discovery.api
> using standard features of Sling. The discovery.api provides a view of a
> topology consisting of a number of individual sling-instances. The instances
> are loosely coupled, except for being part of the topology they do not
> implicitly or necessarily share anything else. For those instances though
> that form a cluster - ie when connected to the same repository - the api has
> an abstraction called ClusterView.
> The discovery.impl uses two mechanisms for discovering other instances:
> * it stores information about the local instance at a unique location in the
> repository. Thus allowing other instances that access the same repository to
> see and recognize each other.
> * it connects to 'remote' instances via a plain HTTP POST, announcing the
> instances that it can see, and getting back the instances of the counterpart
> All of the above is done regularly using a heart-beat - thus allowing to get
> a view of the currently live instances.
> The discovery.api additionally supports leader-election within a cluster: it
> ensures that one and only one instance is elected leader and stays leader
> until it disappears/shuts down/dies. The discovery.impl uses repository-based
> voting between the instances of a cluster to establish a common 'cluster
> view'. Based on an established view, the discovery.impl is then able to
> deterministically elect one of the instances of the view as the leader
> (namely the one with the lowest 'id').
> Also, to support the PropertyProvider concept of the discovery.api, the
> properties of each instance are propagated to the other instances using the
> heartbeat as piggyback (either via the repository or via HTTP POSTs for
> remote instances).
> To get an idea of the discovery.impl build and add and start the two bundles
> (org.apache.sling.discovery.api and org.apache.sling.discovery.impl) to your
> sling installation and open the browser to the provided, simplistic 'topology
> webconsole' at
> http://localhost:4502/system/console/topology
> Please let me know if anything needs further explanation, details. Looking
> forward to having this included in Sling!
> Cheers,
> Stefan
> --
> [0]
> http://svn.apache.org/repos/asf/sling/trunk/contrib/extensions/discovery/api
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