In my post, The Strangler-Fig Pattern Has An Implementation Order; Outputs First, I mentioned The Writeback Anti-Pattern. Turns out, that this anti-pattern hasn’t been named and described before; so I get to be first!
The Writeback Anti-Pattern is when a new Source Of Truth has to write data back to the legacy Source Of Truth because consumers are still getting data from the legacy source.
The Anti-Pattern allows you to pretend that the new system is indeed The Source Of Truth, and the legacy system has become an adapter. This is a lie that lets teams declare success and get the new system into production.
The reality is that the new system is really just another bolt on to the old. The new system now needs to transform all the inputs into the old format, creating tons of technical debt. You have the data model you want, the data model you don’t want, and all the business logic in between.
Another way to explain it, is that the new system tried to do a strangler-fig backwards. Instead of inserting itself between the old system’s outputs first, the new system intercepted the inputs. For the strangler-fig pattern to work it needs to replace the outputs first, or both the inputs and outputs simultaneously. Redirecting the inputs first leads to The Writeback.
