Yeah, but writing a big chunk of new code always involves either gambling or cargo culting, until you nail the actual requirements and the design. MSA is just a

Yeah, but writing a big chunk of new code always involves either gambling or cargo culting, until you nail the actual requirements and the design. MSA is just a methodology to contain risks from the uncertainty, and it never says you must build everything in MSA. It's often better to migrate mature code into (semi-)monolithic services.