This could be achieved by good architecture and system design. You should have various aspects of your application configurable and independent enough to enabl

This could be achieved by good architecture and system design. You should have various aspects of your application configurable and independent enough to enable you to develop an alternative system and make a small downtime migration. Many of scaling issues I see in startups, and stories told by devs in startups, seem to be because corners are cut to make the MVP and push it to the market as quickly as possible, and then suffer scaling woes due to poor design and architecture choices.