Dear systemd folks,
the setup is as follows. Nginx is used as the Web server, which communicates with a Ruby on Rails application over a socket. Puma [1] is used as the application server. Nginx and Puma are managed by systemd service files. If a new version of the application is installed, the goal is that there is no downtime. That means, until the application with the new code isn’t ready yet to serve requests, the old application still answers them, that means, not only are no requests lost, but during restart the visitor does not need to wait any longer than normally. In this case, JRuby is used, which means that application start, `sudo systemctl start web-application.service` takes more than 30 seconds. So, `sudo systemctl restart web-application.service` is not enough as Puma takes some time to be started. (The socket activation described in the Puma systemd documentation [2] only takes care, that no requests are lost. The visitor still has to wait.) Is that possible by just using systemd, or is a load balancer like HAProxy or a special NGINX configuration and service file templates needed? My current thinking would be, that a service file template for the Puma application server is used. The new code is then started in parallel, and if it’s done, it “takes over the socket”. (No idea if NGINX would need to be restarted.) Then the old version of the code is stopped. (I don’t know how to model that last step/dependency.) What drawbacks does the above method have? Is it implementable? How do you manage such a setup? Thanks, Paul [1] http://puma.io/ [2] https://github.com/puma/puma/blob/master/docs/systemd.md
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