I am trying to understand the difference between Solr distributed search and the concept of federated search. Can I uses Solr distributed search to implement federated searches? The requirement is that there are two or more domain models exists and each such domain system indexes its own data to lucene based index. Now I have an interesting use case that I should be able to do a federated search for a single query cutting across different domain systems having its own index.
No, distributed search is not the same as federated.
Federated search" is the term more typically used when searching across heterogeneous data sources - think about things like meta-search engines, as a common example of this.
Distributed search is when you have a homogeneous data source, but it needs to be distributed in order to scale properly.
(taken from here - http://wiki.apache.org/solr/FederatedSearch)
About second question - is it possible to implement federated search using Solr - I'm pretty sure it's possible, the only question is - how much effort it will require from you.
I could see possible solution to create a separate collections in Solr and query them, and later merge all results in query time, but it just a raw idea.