How to Merge Two indices into Single using Logstash

Hi Team

I am having Elasticsearch Cluster of version 7.8.0 running with multiple indices without a pattern in their names.

I want to merge two indices into single index and both [ source ] do not have common field.

I am thinking to use logstash for this purpose.

I want to implement below conditions.

  1. To make each record unique , I am thinking to add a field "_id" that will hold data of index1._id and index2._id, in target index.

  2. When delete will happen on Source index1 , how will it delete records from target index.

Similarly when delete will happen on index2, how will that record be deleted from target index.

Could you please help me in this implementation and guide me.

Thanks
Tushar Nemade