MongoDB has integrated text search features, as we saw in the previous recipe. However, there are multiple reasons why one would not use the Mongo text search feature and fall back to a conventional search engine like Solr or Elasticsearch, and the following are few of them:
The text search feature is production ready in version 2.6. In version 2.4, it was introduced in beta and not suitable for production use cases.
Products like Solr and Elasticsearch are built on top of Lucene, which has proven itself in the search engine arena. Solr and Elasticsearch are pretty stable products too.
You might already have expertise on products like Solr and Elasticsearch and would like to use it as a full text search engine rather than MongoDB.
Some particular feature that you might find missing in MongoDB search which your application might require, for example, facets.
Setting up a dedicated search engine does need additional efforts to integrate...