[sgt]

There are many solutions for this. Many are complex and will probably take time to implement right now, and you just want to focus on your app in the next days.

So if you want something super simple that will cause no downtime while switching over to a new version, just run two instances of your service, one on e.g port 9000 and the other on 9001.

At any time your proxy (nginx or traefik etc) will use only one of these.

Once you upgrade the version for the inactive one, you change the port used in nginx and reload it. Then the new version will be used.