Doesn't fivetran/hightouch do this?
We’ve worked with some folks who were cobbling together ELT and rETL to achieve a type of two-way sync, but they faced three problems with this approach: most importantly, handling for infinite loops, where an insert in one data source triggers an insert in the other, which then gets picked up anew, etc. Second, it wasn’t clear how to handle merge conflicts when the same record is edited from both sides (we give priority to the primary source). Finally, it was frustrating to debug problems when having to log into two separate tools.
It's an immature tool, so I don't yet know that I can claim we've spent _less_ than Fivetran on the additional engineering and ops time, but it feels like it has potential to do so once stabilized.
Right now, we're focusing on use cases that require changes to be synced within a minute. Fivetran and its ilk are generally more focused on large data batches at less frequent intervals (e.g., to unlock 1-minute syncs at Fivetran, you must be on the Enterprise plan, whereas we offer that out of the gate with the Starter plan).
I've always been surprised that fivetran/hightouch don't ever throw in a .reverse().
That’s one reason why people trying to stand up two-way syncs have been stuck with dated tech (Heroku Connect) or have had to build in-house.