If you are going to coexist endpoints, you need a way for callers to route their requests accordingly. For systems making use of HTTP, I have seen this done with both version numbers in request headers and also in the URI itself — for example, /v1/customer/ or /v2/customer/. I’m torn as to which approach makes the most sense. On the one hand, I like URIs being opaque to discourage clients from hardcoding URI templates, but on the other hand, this approach does make things very obvious and can simplify request routing.
