[01HNNWZ0MV43FF]

At one job, Nginx facilitated blue-green deployments. I would spin up a 2nd app server and have Nginx cut-over to it with <1 second of downtime. If anything went wrong, the rollback plan was to only roll back the Nginx config.

I automated all that with a few scripts that included sanity checks with `nginx -t`. After the update looked good I would shut down the old app server without any time crunch. Only the Nginx config was time-sensitive.

I'm not sure if you can do that without some kind of reverse proxy as an abstraction layer. At least a TCP-level proxy.

And as everyone said, virtual hosting.

[MayeulC]

In theory, you can do even better with no reverse proxy: hand down the open sockets to the new version of your application, zero downtime at all. (Nothing prevents you from having a reverse proxy in front while doing that).