I have a service with hundreds of requests per day, thousands of users, it is an old RoR app that is impossible to update now, 3 major versions behind latest, s

I have a service with hundreds of requests per day, thousands of users, it is an old RoR app that is impossible to update now, 3 major versions behind latest, several dependencies that can't be built on newer Ruby versions. Even the Ruby version it is using can't be build anymore on more recent OSs because of OpenSSL incompatibilities. It will take hundreds of hours to be updated, which at some point will be almost (or even less) than building it again from scratch. As I do not have this time, it will probably die a slow death.