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From André Warnier>
Subject Re: JK 1.2.28 - load balancer worker fails on startup with one worker down ?
Date Thu, 16 Apr 2009 06:16:16 GMT
Scott Bradshaw wrote:
> Yep - you are right on.
> The machine was taken off the network and moved to a test network for a few
> days. It currently does not resolve. If I change the host to its old IP
> address (which does not respond), the system starts up just fine.
> I would expect to see an error in the log, but just because 1 host does not
> resolve, I wouldn't expect mod_jk to prevent the rest of the hosts from
> functioning. In the current configuration I just changed, the IP address I
> have now is not functioning and could be a configuration error, but mod_jk
> is still loading.
> How do I go about submitting this as an enhancement request for the next
> version?
Still continuing to guess..

This is about efficiency.
If mod_jk had to do a DNS lookup each time it wants to send a packet to 
a backend Tomcat (or at least each time it wants to create a new 
connection to a backend Tomcat), that would be very inefficient.

So, instead, mod_jk stores the IP address of each backend Tomcat, and 
during normal operation uses only that stored IP.

But, as a convenience, in the configuration file, it allows you to 
specify the worker's host as a name if you wish; and if you do that, it 
does the lookup once at startup, to resolve that to an IP which it stores.

But if it cannot at startup do this lookup and resolve the name to an 
IP, then it is stuck and cannot go further.
Because if it did go further, then it would have to store this 
workers'host as an unresolved name, and then it would have to do a 
lookup during normal operation.

Now, I have really no idea if the code is really like that, but if not 
at least it seems logical, doesn't it ?

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