---+ Falcon Atlas Bridge

---++ Falcon Model
The default falcon modelling is available in org.apache.atlas.falcon.model.FalconDataModelGenerator. It defines the following types:
<verbatim>
falcon_cluster(ClassType) - super types [Infrastructure] - attributes [timestamp, colo, owner, tags]
falcon_feed(ClassType) - super types [DataSet] - attributes [timestamp, stored-in, owner, groups, tags]
falcon_feed_creation(ClassType) - super types [Process] - attributes [timestamp, stored-in, owner]
falcon_feed_replication(ClassType) - super types [Process] - attributes [timestamp, owner]
falcon_process(ClassType) - super types [Process] - attributes [timestamp, runs-on, owner, tags, pipelines, workflow-properties]
</verbatim>

One falcon_process entity is created for every cluster that the falcon process is defined for.

The entities are created and de-duped using unique qualifiedName attribute. They provide namespace and can be used for querying/lineage as well. The unique attributes are:
   * falcon_process - <process name>@<cluster name>
   * falcon_cluster - <cluster name>
   * falcon_feed - <feed name>@<cluster name>
   * falcon_feed_creation - <feed name>
   * falcon_feed_replication - <feed name>

---++ Falcon Hook
Falcon supports listeners on falcon entity submission. This is used to add entities in Atlas using the model defined in org.apache.atlas.falcon.model.FalconDataModelGenerator.
The hook submits the request to a thread pool executor to avoid blocking the command execution. The thread submits the entities as message to the notification server and atlas server reads these messages and registers the entities.
   * Add 'org.apache.atlas.falcon.service.AtlasService' to application.services in <falcon-conf>/startup.properties
   * Link falcon hook jars in falcon classpath - 'ln -s <atlas-home>/hook/falcon/* <falcon-home>/server/webapp/falcon/WEB-INF/lib/'
   * In <falcon_conf>/falcon-env.sh, set an environment variable as follows:
     <verbatim>
     export FALCON_SERVER_OPTS="$FALCON_SERVER_OPTS -Datlas.conf=<atlas-conf>"
     </verbatim>

The following properties in <atlas-conf>/atlas-application.properties control the thread pool and notification details:
   * atlas.hook.falcon.synchronous - boolean, true to run the hook synchronously. default false
   * atlas.hook.falcon.numRetries - number of retries for notification failure. default 3
   * atlas.hook.falcon.minThreads - core number of threads. default 5
   * atlas.hook.falcon.maxThreads - maximum number of threads. default 5
   * atlas.hook.falcon.keepAliveTime - keep alive time in msecs. default 10
   * atlas.hook.falcon.queueSize - queue size for the threadpool. default 10000

Refer [[Configuration][Configuration]] for notification related configurations


---++ Limitations
   * In falcon cluster entity, cluster name used should be uniform across components like hive, falcon, sqoop etc. If used with ambari, ambari cluster name should be used for cluster entity