Both versions of an API can run behind haproxy as well, and requests can be switched between them based on many different criteria from OSI layer 4 on up. I gue

Both versions of an API can run behind haproxy as well, and requests can be switched between them based on many different criteria from OSI layer 4 on up. I guess I just don't see what was novel or interesting about the basic idea of switching between two implementations that satisfy a declared interface. It was just a few years back that DI was all the rage.