If it hits the same database, build the new features in the new stack, and launch them. Users should click from the old to the new without even realizing. You h

If it hits the same database, build the new features in the new stack, and launch them. Users should click from the old to the new without even realizing. You have to figure out some details like sharing sessions, but this way avoids adding onto the old application. Otherwise you'll never catch up.