[sb8244]

A small tweak to the "old style" plan that I'd look at is running the new service in parallel with the old but not actually taking customer facing action. For example, send all writes to the new microservice when the write happens in the monolith.

Pros: Gives a real work indicator of performance with very low risk. Data could be truncated and then backfilled before the final release.

Cons: not always possible depending on complexity or feature. Requires implementing the parallel path which carries some risk in itself.