Mainframe applications provide solid transaction processing with a high degree of scalability and predictable costs. By exposing 1st class APIs via middleware, you can evolve the front end and back end independently.

ESB on-prem or cloud provides API integration with CICS/IMS transactions. An alternate approach is to deploy Liberty to CICS-based applications to enable a Java layer with REST/SOAP capabilities in the CICSPLEX.

Modern JS front ends with well-defined back end APIs leveraging transactions from CICS/IMS provide a robust, scalable maintainable Application Architecture.

Mainframe Applications can participate in Event-based architectures. MQ series provides a transactional queuing fabric to allow CICS/IMS transactions to publish events as master data changes or transactions execute. Inbound events can be routed to the required transactions by building a long running routing transaction that dequeues event messages and schedules the required transactions.