[ClusterLabs Developers] RA as a systemd wrapper -- the right way?

[Valentin Vidic]

On Fri, Oct 13, 2017 at 02:07:33PM +0100, Adam Spiers wrote:
> I think it depends on exactly what you mean by "synchronous" here. You can
> start up a daemon, or a process which is responsible for forking into a
> daemon, but how can you know for sure that a service is really up and
> running?  Even if the daemon ran for a few seconds, it might die soon after.
> At what point do you draw the line and say "OK start-up is now over, any
> failures after this are failures of a running service"?  In that light,
> "systemctl start" could return at a number of points in the startup process,
> but there's probably always an element of asynchronicity in there.
> Interested to hear other opinions on this.

systemd.service(5) describes a started (running) service depending
on the service type:

simple  - systemd will immediately proceed starting follow-up units (after exec)
forking - systemd will proceed with starting follow-up units as soon as
          the parent process exits
oneshot - process has to exit before systemd starts follow-up units
dbus    - systemd will proceed with starting follow-up units after the
          D-Bus bus name has been acquired
notify  - systemd will proceed with starting follow-up units after this
          notification message has been sent

Obviously notify is best here but not all daemons implement sending
sd_notify(READY=1) when they are ready to serve clients.

-- 
Valentin