I am looking for 2 things mod_proxy_balancer cannot currently provide:
1. Something to limit the maximum impact of having many dead members
under a load balancer on normal requests.
* The process of discovering that dead workers are still dead
shouldn't overtly impact any normal request (assuming there
are live workers available)
* Sample situation:
o Load balancing over 10 ports, most of which do not
have an active backend (Tomcat) associated at the
time. If there is only 1 backend alive, every 'retry'
seconds, a normal request is delayed by a period of
9*dead-connection-latency. That's neither necessary
nor acceptable.
* Possible solutions include:
o Having an option to have a background thread ping the
backends rather than allowing normal requests to do so.
+ In the case of mod_proxy_ajp, a cping would be
preferred here, rather than a full request.
o Limiting the number of workers any single normal
request will attempt to recover
2. Something to reduce the severity of log messages when discovering
that a dead worker is still dead.
* There is no need to fill the error logs with notices that a
worker that has been dead is still dead. This is good
troubleshooting info and should be logged, but at a lower
severity level that does not show up in the logs by default.
* Depending on the solution to (1), this might just fall out
of that.
I had already started a discussion along these lines on the Tomcat
development mailing list, as I have the same needs for both
mod_proxy_ajp (for Apache 2.2 front ends) and mod_jk/isapi (for IIS
front ends). Mladen Turk kindly pointed me to some work he had recently
done on trunk for mod_jk to add a background "watchdog" thread for
periodic background work. He has also talked about adding a similar
capability to Apache itself in the future. Jim Jagielski pointed out
that the discussion should probably move over here as portions have
impact on Apache itself.
I need solutions to these problems one way or another, so if nothing
else I'll have to hack in something into our own fork of the code.
I have a fair amount of time to solve these problems, however, so I'd
much rather see them solved in a good, general way that can be a
value-add part of both mod_jk and mod_proxy -- rather than a one-off
fork. Ideally the solutions would be somewhat consistent as well, for
everyone's sanity.
Thoughts? Suggestions?
--
Jess Holle
