> - it has been developed for 12 years directly on production with no source control ( hello index-new_2021-test-john_v2.php )
First step would be to get that into source control.
> - the routing is managed exclusively as rewrites in NGInX ( the NGInX config is around 10,000 lines )
This might be a benefit actually. I'd just start a new application and route to the new code one-by-one using the Strangler approach.
> - it has been developed for 12 years directly on production with no source control ( hello index-new_2021-test-john_v2.php )
First step would be to get that into source control.
> - the routing is managed exclusively as rewrites in NGInX ( the NGInX config is around 10,000 lines )
This might be a benefit actually. I'd just start a new application and route to the new code one-by-one using the Strangler approach.