[Spread-users] Spread startup
iane at sussex.ac.uk
Wed Sep 27 06:18:44 EDT 2006
--On 26 September 2006 12:07:39 -0400 Theo Schlossnagle <jesus at omniti.com>
>> Well, hostname is always set correctly by the time I can get to log
>> in, it's set in /etc/hostconfig. The IP address is set by DHCP, so
>> it's not in /etc/hosts.
>> Perhaps that's an alternative solution, but I think Spread would
>> ideally check that it has local access to one of the IP addresses
>> in the spread_segment definition before starting. Does it not do that?
> Most server software is pretty particular about startup order /
> dependencies. It sounds like you are trying to compensate for a lack of
> this on the Mac. I was unaware that Mac launchd suffered form this (I
> thought it was a rather thorough startup system). Spread and wackamole
> require certain things in the system to be functioning correctly before
> they start -- otherwise, the outcome will likely not be the desired
Well, launchd is a thorough startup system. However, the launchd philosophy
is to design "daemons to not depend on the order in which they are started.
Programs should be robust in the case where a service is unavailable, and
in some cases, programs should be automatically spawned when needed instead
of requiring programs to wait for them."
Legacy startup mechanisms are available (rc scripts, cron, "StartupItems",
inetd, etc), but I don't think launchd will ever include a mechanism for
ordering startup. launchd replaces *all* those mechanisms, btw, where
daemons are suitably coded.
Having said all that, a script can use launchd to start and stop services,
so ordering is possible.
launchd does have a number of great advantages over traditional startup
mechanisms. In particular, it has a watchdog role which will restart
crashing daemons. That feature alone makes it highly desirable to use
> I would not be using DHCP to run these things. The IP addresses are
> hardcoded into the spread.conf, but not into your hosts' configurations.
> This is an inconsistency.
Well, the IP addresses aren't dynamic - in the sense that the DHCP server
is configured to give each host the same primary IP address each time.
IT Services, University of Sussex
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