Elastic & Relational DB

I’m having difficulty understanding how to architect the back-end of a search application which will require searching over 1m+ documents and would like some advice on the following as it relates to using a lucene based index and a relational store:

  1. Should the UI only search against Elastic and the primary relational store act as a good copy store?

  2. If my data is inherently relational (let’s say I have two tables, recipes mid ingredients) that rely on joins, how will I present search results to the user when they’re data is being searched against and presented from only elastic?

  3. When users make edits to the data, the updated edits get stored in the relational store. Would I then kick off a re-index of elastic of the delta so it becomes immediately searchable in the application? More of an opinion.

I believe my lack of understanding stems from not knowing the interplay between elastic and a traditional DB. Any advice would be helpful.

Elastic & Relational DB