Henri Gomez wrote:
David Rees a écrit :
Henri Gomez said:
Henri Gomez a écrit :
Nope since you don't have to just test at protocol level but also on higher level, for instance check the full chain, up to servlet handling.
It's easy to simulate this behavior by sending a STOP signal to Tomcat.
I've also attached a log from mod_jk showing the problem. I marked the point at which processing in mod_jk stopped until I sent a CONT signal to tomcat.
Does mod_jk2 have this same problem? Is there any interest in fixing this? Does anyone have a workaround for this issue?
Well, if you have a hung tomcat, you're probably allready in serious trouble.
No, actually in my case I wasn't. I had two Tomcats running, as one was
prone to locking up due to a JVM or application bug. With a 50-50 load
distribution between two Tomcats, this left me with 1/2 of the requests
getting stuck and clients waiting forever and tying up Apache processes. Eventually, a DOS will be the result if action is not taken in time. If
mod_jk noticed it wasn't really alive, this wouldn't be an issue at all.
Anyway, if we add stuff like time-out in ajp request, you could be stuck with long running servlets. Also jk read request in a blocking mode for performance and adding timeout here is not an option.
Agreed that we wouldn't want a timeout normally to handle normal long running servlet processes, but if there was a PING/PONG added to the protocol there should be a timeout to prevent the above situation.
When I worked on ajp13++ (ajp14) protocol, I added a more secure auth mecanism at connection time.
Since there is a bidirectionnal communication, jk could detect that even if the connection is open, the remote didn't respond and so fall back to the next in cluster configuration.
But on allready established connections, the problem persist.
Or we should add a PING/PONG before sending any request to tomcat.
It could be done as optional but I work on it only if many users make such requirements
if many users ask for such feature ;)
Well, you've got one so far. ;-) Adding a configurable option to have
mod_jk verify (PING/PONG) that Tomcat is actually responding before using
the connection would solve the problem and I can't imagine that it would
add a lot of complexity to the code as well. If I wasn't so rusty with my
C programming and had some spare time, I would offer to help code it up. ;-) In any case, I'll be more than happy to help test.
Well, if you could find more users or at least one tomcat commiter (Glenn, Remy, Costin, JFC...) who need it, I'll add the necessary code in java and C areas ;)
There may be a simple way to achieve what David is asking for without setting a request timeout or implementing a PING/PONG between mod_jk and Tomcat.
What if each worker tracked the number of requests which were handled by the worker since the last successful completion of a request.
i.e. add the following to a worker
worker->last_completed // Time in seconds since last successfully completed request worker->requests_since_last_completed // Number of requests sent to worker since last successful completion.
Then logic could be added to try and detect an instance of Tomcat which has failed. Perhaps even allow several additional worker properties to determine when mod_jk should consider the worker failed.
The idea needs to be flushed out some more. But we should be able to track enough data about how a worker is performing to make some simple decisions.
Glenn
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