Deprecate and remove the reload hook

[christophermaier]

Based on #5306 the intended purpose of the reload hook is unclear.

Based on

habitat/components/sup/src/manager/service/mod.rs

Lines 272 to 295 in 01de8a1

	/// Runs the reconfigure hook if present, otherwise restarts the service.
	fn reload(&mut self, launcher: &LauncherCli) {
	self.needs_reload = false;
	if self.process_down() || self.hooks.reload.is_none() {
	if let Some(err) = self.supervisor
	.restart(
	&self.pkg,
	&self.service_group,
	launcher,
	self.svc_encrypted_password.as_ref(),
	)
	.err()
	{
	outputln!(preamble self.service_group, "Service restart failed: {}", err);
	}
	} else {
	let hook = self.hooks.reload.as_ref().unwrap();
	hook.run(
	&self.service_group,
	&self.pkg,
	self.svc_encrypted_password.as_ref(),
	);
	}
	}

, it appears that reload is intended to be a substitute for restarting the service, but it's not clear how this can actually work in practice, given that the Launcher is the thing that owns the actual process.

If we re-organize the hook invocations as detailed in #5306, it's unclear what reload is really accomplishing. It is likely that it is a vestige of the time before the Launcher, and possibly before the multi-service Supervisor; we may lose nothing by removing it (subject to appropriate deprecation notices, of course).

There are several other issues for hooks and other methods of dealing with various aspects of service shutdown that may be interesting to consider here:

• Request: lifecycle hooks for before kill signal #4923
• [feature request] Allow user defined stop hook #5135
• Configurable kill signal and timeout #2447

[baumanj]

it appears that reload is intended to be a substitute for restarting the service, but it's not clear how this can actually work in practice, given that the Launcher is the thing that owns the actual process

Can you elaborate? Launcher owns the process, but the supervisor can still kill it and direct launcher to restart it. I must be missing what you're getting at.

[christophermaier]

I mean that I'm not clear what running a script (the alternative to which is having the Launcher restart a service) would do to "reload" a service that wouldn't mess up the bookkeeping that the Launcher already does.

[baumanj]

Ah, I think I understand. If I think of it in terms of what is possible with load/unload, it would make sense that it could be used as a signal to changes of bindings and such. Would in make more sense if we had something like hab config edit?

[christophermaier]

I haven't fully plumbed the depths of Git history on this yet, but it seems that at some point that reload was actually intended as reconfigure: 9e1203f, but somehow we ended up with both.

I'm not sure exactly how these wires got crossed, but if that is the case, it does suggest that reload could go away.

[christophermaier]

See also #1838

[davidMcneil]

Resolved by #6668