I'm very new at WSO2 stack and wonder when I should use WSO2 ESB proxy service and when – create business process via BPEL?
I think they are doing the same thing – performing a task via services composition and some mediation.
There is a fundamental difference between ESB and BPEL.
The role of ESB is to provide various non-functional properties to the business requests. ESB is thus used for e.g. mediation, transformation, security and virtualization/proxying of the requests. While it can do some simple message-enrichment using sequence diagrams, its primary purpose is to mediate messages between various services/hosts in the system.
On the other hand, BPEL is dedicated to implement business services and handle complex business workloads. Therefore, the role of the BPEL is to provide the functional properties to the business process- e.g. implementing the actual business process logic.
ESB and BPEL thus together deliver the separation-of-concerns which is often emphasized by component and service-oriented architectures.