I just released first version of elasticsearch river, which allows to open
Atlassian's JIRA content for fulltext search.
It uses REST API available in JIRA 5+ to grab informations from JIRA.
Both issues and issue comments can be stored into search index. You can
flexibly configure document structure stored into search index (or use
default one), and then create mapping meeting your search needs.
Fell free to use it and send feedback.