[systemd-devel] Smooth upgrades for socket activated services

[Michael Biebl]

Am Mo., 20. Feb. 2023 um 11:06 Uhr schrieb Mike Hearn <mike at hydraulic.software>:
>
> Hi,
>
> I'm exploring socket activation as part of work on a tool that makes
> systemd-controlled servers easier to deploy and use. Given a config
> file the tool builds a package that contains the app and systemd
> units, uploads it, installs it with dependency resolution, the
> postinst scripts start the service etc. It's sort of a Docker
> alternative that's more classically Linux-y, designed for a world
> where really big machines are really cheap and thus many apps don't
> need to be cattle-ized. Pets are sometimes OK.
>
> As part of this I'm looking at how to make upgrades smooth. Socket
> activation already allows you to shut down, upgrade and restart a
> service without dropping connections because systemd will hold the
> connections until the service comes back but there are a couple of
> aspects that weren't really clear to me from reading the excellent
> "pid eins" blog post series. Could we maybe get a new blog post
> exploring these issues?
>
> 1. How exactly should you stop a service that's socket activated so it
> won't be re-activated during the upgrade but new connections won't be
> lost, e.g. in package scripts that are executed across upgrades.
> Currently the scripts stop the service before the upgrade happens,
> then restart afterwards.

Currently, there is no way to "freeze" the execution of a socket
activated service.
A feature I'm missing as well, fwiw.