I believe the last slide shows that the restart takes 48 milliseconds, and I get similar results with one of my own processes running on our server. This doesn't seem like a big deal at all.
For large node programs, this approach may require careful optimization of the start process in the same way that we optimize the client-side page loading process.
Chad_oliver is right: the impact is negligible. We wouldn't do it if it would deteriorate the user experience.
There's a lot of great documentation on the systemd site. An exact description of socket activation and its intended use cases is on there as well: this is definitely one of them.
different node processes start up differently, some can take a while. auto-quit after 5 minutes, really? socket activation is helpful for lazily loading things when a system boots up, so everything can be started in parallel and the order that processes come online doesnt matter. its been adapted to all kinds of things and im not saying it wouldnt work in some use cases to conserve resources, but socket activation + auto quit is a bit odd. node actually benefits from running for a long time or from being hit with a lot of requests -- even if your app starts fast you are trading this away among many other things...
For large node programs, this approach may require careful optimization of the start process in the same way that we optimize the client-side page loading process.