I agree that legacy apps break 12 factor rules. That's why the 12 factor app is "a thing" in the first place. An app which follows them can survive being killed

I agree that legacy apps break 12 factor rules. That's why the 12 factor app is "a thing" in the first place. An app which follows them can survive being killed and restarted. I've worked on some legacy migrations and it's usually a process of incrementally chiselling out services and cleaning up hard-coded assumptions. Tedious but usually doable.