Legacy Monolith Migration for a Logistics Operator 

The system running this operator's eighteen warehouses was a .NET Framework application first deployed in 2011. The two developers who understood it had both left. Nightly batch jobs were stretching toward morning, and the business wanted live shipment tracking that the old architecture simply couldn't host.

Management had been burned before by a big-bang replacement pitch from another vendor. What they asked us for was the opposite: change the engine without ever stopping the truck.

We spent the first two weeks doing nothing but archaeology: reading code and tracing batch jobs until we knew which modules actually mattered. Then a team of seven began strangling the monolith one capability at a time, routing traffic through an API gateway so each new .NET 8 service on AKS could take over a slice while the old system kept serving the rest.

The ordering module nearly caught us out. Traffic diffing between old and new showed pricing mismatches on about one order in two hundred, and the culprit was an undocumented stored procedure handling contract-pricing edge cases that existed nowhere in the application code. We froze that cutover for three weeks, ported the logic with a test suite reproducing every case we'd seen in the diff, and only then flipped the switch. Nobody in the warehouses noticed either the freeze or the flip, which was the whole point.

Eleven months in, the monolith was down to a scheduling stub, API response times had dropped by more than half, and the live IoT tracking dashboards were running on the same event stream the new services already produced.