The Message Bus role runs on Rebus and is a message transport mechanism which allows application roles to communicate across boundaries.
You can host the Message Bus role on:
Azure Service Bus
If you are upgrading from Sitecore 9.1 to 9.2, Sitecore does not provide a tool for migrating from SQL to Azure Service Bus.
Refer to the Sitecore compatibility table for compatible versions.
The Message Bus role has its place in the Sitecore reference structure. It can be referenced by other roles, and it can also reference other roles.
The Message Bus role is referenced by the following roles:
The Message Bus role does not reference other roles.
Privacy and security
The Message Bus role does not handle personal data by default and privacy concerns are described by the referencing roles.