Design Search service using elastic search

I have a requirement. I am building up a search service for a social network. The search service should return the name of the users that somebody searches. Now it will be limited to user domain search only. I am planning to use elastic search to keep the indexes(user domain details). I will then call the EL from my search service(The search service is on nodejs). I am not able to think of a design on how to create the indexes for EL. Should I use a batch to create the indexes or during creation of users I will create the index.

A good pointers or a good design will be appreciated.