ElasticSearch RoutingMissingException
When you have a parent child relationship, you need to specify the parent in the URL each time you try to access it a child, since routing now depends on the parent.
In your example, you'd want to try:
http://example.com/myindex/comment/12345?parent=[article_id]
Had typo in mappings.
comment: mappings: article_id: <-- was "article" type: long index: not_analyzed
Maybe this helps someone :)