Why need another Nosql when we can save the document in elastic search

Question

Here is one sample diagram below. We can pass from Rails Server to Elastic-Search server. Why we require Mongo or any other db as main database and the source of truth

Answer 1

In short Elasticsearch is not aiming to be primary database and not intended to replace the databases, it doesn't offer RDBMS system ACID properties, I know in your case you are using NoSQL like MongoDB so ACID or transaction is probably you are not looking for.

But data loss and resiliency becomes very important when you use it as a primary database and although Elastic is working very hard to improve it continuously still if you are storing critical data then I would suggest to compare MongoDB and elasticsearch wrt to resiliency and take decision according to that.

This is an excellent answer related to your question, Please go through it.