Ask HN: Communication between domain specific services

Hi HN!

We're in the processing of deploying a series of internal domain specific services (Ala Microservices)

I'm currently investigating the best mechanism for communicating data between them, For example service A gets a list of data which includes an ID or ID's of an object in service B.

Would a simple REST API that takes a list of ID's on Service B work well enough or would a Pub/Sub Bus between services be better suited, or a third option I've not listed here?

The services are likely to independently hold O(10M) records.