Micro services architecture for search engine

I am going to build a search engine based on microservices architecture. My idea was a service for crawling, a service for scraping, a service for indexing and a service for ranking. As I know each service must has its proper database. I am asking on each database to associate for each service (mongo db, dynamo db, elastic search, cassandra, ...) and how to communicate between the data stored in each service in a fast way.