[Spread-users] Spread startup

Ian Eiloart 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
> outcome.

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.

Ian Eiloart
IT Services, University of Sussex

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