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From Rainer Jung <>
Subject Re: Apache fails to start when .host does not resolve.
Date Tue, 01 Apr 2008 20:50:41 GMT
fredk2 schrieb:
> Hi,
> when you set a load balancer (mod_jk v1.2.26) with 2 workers:
>     worker.myWorker.type=lb
>     worker.myWorker.balance_workers=tc1Worker, tc2Worker
> and one of the worker's host cannot be resolved:
> Then Apache will not start.
> - since the other worker is 'good', should'nt we let apache start with a
> nice error message informing you that one worker could not resolved (done
> today) and jk will disable the worker and let apache start anyway?
> - Adding a disable does not fix the issue it seems.  Only removing the
> worker from the list does.
>     worker.tc2Worker.activation=d

Yes that's the way it was implemented intentionally.

> The idea is that if DNS fails to resolve a host (some admin mistake) and
> Apache was restarted automatically for unrelated reasons, it would fail to
> come back online without a manual intervention - editing a configuration
> file (which might be a challenge).

In general I think it's better to not start, if a worker is completely 
broken. Yes, in your case it would provide a problem with regular 
restarts, but we could argue, that if your DNS is not rock solid, but 
your production systems depend on IP address resolution, then you should 
either use the IPs in the workers host attribute, or add the few systems 
you need to contact from your httpd to your hosts file. Of course that 
contradicts the major goals of DNS, but if you want to stick to those 
you really need a rock solid DNS (which is not that hard). Admin 
failures when managing critical DNS data are really major incidents.

If we allow unresolvable host names, it's very likely that users will 
not notice the resulting error messages during startup. And I think it's 
much more likely that people simply put typos into the host names than 
the occurence of local DNS failures.

This seems to be grey area, where there's no obviously best solution.

> Rgds - Fred



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