----- Original Message ----- From: "Glenn Nielsen" <[EMAIL PROTECTED]> To: "Tomcat Developers List" <[EMAIL PROTECTED]> Sent: Wednesday, September 24, 2003 12:28 PM Subject: Re: mod_jk does not detect a hung Tomcat
> > > 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. This won't work with the pre-fork MPM, since each Apache child will have its own idea of the timing. The only way that it could tell that a Tomcat failed is to try the request and fail :). > > 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 > > ---------------------------------------------------------------------- > Glenn Nielsen [EMAIL PROTECTED] | /* Spelin donut madder | > MOREnet System Programming | * if iz ina coment. | > Missouri Research and Education Network | */ | > ---------------------------------------------------------------------- > > > --------------------------------------------------------------------- > To unsubscribe, e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] >
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