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Design:
Technical Constraints
Navigator, currently, pulls in data periodically from different Hadoop components - HDFS, Hive etc. It uses Solr for indexing. But Navigator does provide a simple Java Client to set and query metadata.
Though it is limited in its features, it can potentially be used to push custom metadata for entities to Navigator. But there few known and unknown issues:
Pushing data seems straightforward using the Java client but subscribing to metadata changes in Navigator doesn’t seem straightforward
Ramification: Users can’t edit business metadata for CDAP entities in Navigator and expect it to reflect in CDAP Metadata system
Tradeoff: Navigator can only read CDAP metadata but can’t modify/write. Any modifications will not be reflected in CDAP Metadata Store.Creating brand new SourceType, EntityType(s) doesn’t seem possible using the Java Client SDK.
Ramification: This is a big blocker if we want the Source Type CDAP at the same level as SourceType of HDFS, Hive, (HBase - missing), Oozie etc. There is a catch all SourceType called SDK but then again EntityTypes doesn’t seem to be flexible to allow new ones.
Workaround: Have to check with Cloudera Navigator team to see what is feasible given our ideal data model. For ex, use SourceType.SDK.SystemMetadata => Technical Metadata - setting this through Java client seems to be not possible.
Ramification: Java client can only alter custom metadata. This might be confusing for users as there is a clear one-to-one mapping between system : technical :: business : custom metadata.
Tradeoff: Don’t push System metadata. Only publish business metadata. Or publish system metadata fields as ‘custom metadata’ in Navigator.UI Rendering for different Source/Entity combinations: If we do manage to setup custom CDAP SourceType, not quite sure how the UI rendering will work for the same. It is fairly simple for most of the SourceTypes (with special tags for say Hive Table schema) but have to confirm if there is support by default for other types.
Ramification: Lose out on potentially enriched user experience
Architecture Design
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There will be a system service to push our metadata changes to external metadata management system. This is an optional system service that can be enabled using cdap-site.xml and a pluggable external system can be chosen. For this work, the external system will be Navigator but in future we can support Apache Atlas. The system service will subscribe to Kafka topic to which metadata changes are published by the CDAP MetadataAdmin. These messages are then pushed to the external system - in case of Navigator we could use the Navigator SDK Java client. We will also have to use a system dataset to store the Kafka offset. Potential downside of this approach is that we will be consuming another valuable container resource in the cluster.
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