Why a Single Service?

In my last post, I illustrated an example where two legacy applications were bundled up to be included in a single CRM service. The question was raised as to why these were not just simply made to be separate CRM services.

The answer comes down to aligning the service definitions with the business. In the majority of businesses, the handling of a VIP customer is similar to that of a regular customer. The two processes have a lot in common. In order to have loose coupling and high cohesion, both of these concerns should then be placed in the same service.

Moreover, the decision as to whether or not a customer is VIP is a CRM concern. We do not want this logic in other services that send requests to the CRM service. If we had two separate CRM services, then each service sending them requests would need to decide which request to send - the VIP CRM service request, or the regular CRM service request. This decision should not be a concern of the requesting service.