WG: TC3.3 updating a webapp without killing sessions
Hi, since Costin is currently refactoring mod_jk in jakarta-tomcat-connectors I want to throw in our usage scenario. We are abusing the loadbalancing feature of mod_jk to switch tomcats on the fly in order to be able to make application updates without killing our curreent user sessions. See discussion below from tomcat-user This feature (graceful restart) was present in jserv and is still missing in mod_jk/Tomcat3.3 as far as I know. Below are references to the archive where Michael Kuz has sent a patch to decouple this feature from the lbfactor (introducing an active flag). So please keep in mind the requirement to be able to update Webapps in a farm of Tomcats without killing active sessions. Thanks, Hans -Ursprüngliche Nachricht- Von: Hans Schmid [mailto:[EMAIL PROTECTED]] Gesendet: Mittwoch, 28. November 2001 18:21 An: Tomcat Users List Betreff: AW: TC3.3 updating a webapp without killing sessions Thanks Larry, perhaps a lbfactor of 0.1 or so would do the job for us. We could probably live with 1 out of 10 sessions beeing sent to the wrong Tomcat and beeing killed if this instance shuts down. Should this be discussed in tomcat-dev ? I remember a patch from early this year which tried to fix this (check the archives) but did never make it into the release It tried to add a flag called 'active' in the worker.properties file for each worker instead of misusing the lbfactor for this. ajp13-01... lbfactor=1 active=0 and ajb13-02... lbfactor=1 active=1 see http://w6.metronet.com/~wjm/tomcat/2001/Jan/msg00102.html and http://w6.metronet.com/~wjm/tomcat/2001/Jan/msg00114.html for the patch which might be a little bit outdated -Ursprüngliche Nachricht- Von: Larry Isaacs [mailto:[EMAIL PROTECTED]] Gesendet: Mittwoch, 28. November 2001 15:00 An: 'Tomcat Users List' Betreff: RE: TC3.3 updating a webapp without killing sessions I assume the value or lbfactor is requested to be 0 because 1/lbfactor is calculated during initialization. Since this is done with doubles, it may generate an internal representation for infinity rather than a division by zero error. I don't have a complete understanding of what mod_jk does internally for loadbalancing, but your approach seems like it should work. A brief scan of the codes shows that some updates to mod_jk would be needed to insure that lbfactor=0 means only use this worker when mandated by session routing. There isn't much logging around the choice of worker. Perhaps adding some logging would help determine why requests are being routed to the lbfactor=0 Tomcat when session routing shouldn't be a factor. Hope this helps. Cheers, Larry -Original Message- From: Hans Schmid [mailto:[EMAIL PROTECTED]] Sent: Wednesday, November 28, 2001 4:25 AM To: Tomcat-User Subject: TC3.3 updating a webapp without killing sessions Hi, We try to make a workaround for the following problems: 1.) memory management 2.) application update 3.) do not kill active sessions Perhaps someone can comment on the startegy and answer some questions. Our environment: Tomcat 3.3 final with mod_jk Apache 1.3.19 on Solaris 2.7 Sparc Our problem: ever growing cache until memory runs out (clearly an application problem) plus soft updates to our application without killing actiove sessions The idea: when a certain ammount of memory is reached by the tomcat java process, start up a second Tomcat and route all new requests to the second instance while existing sessions should phase out on the first instance. If no more sessions are active on the original Tomcat, shut it down (currently we just shut it down 30 minutes after the second Tomcat started up) How to do it with mod_jk: We have two versions of a worker.properties. Before we start up our second tomcat, we switch a link to point to the other version. Both versions of the worker.property file have a loadbalancer worker defined: First version: worker.list=loadbalancer worker.ajp13-01.port=11009 worker.ajp13-01.host=tomcathost worker.ajp13-01.type=ajp13 worker.ajp13-01.lbfactor=1 - important worker.ajp13-02.port=11019 worker.ajp13-02.host=tomcathost worker.ajp13-02.type=ajp13 worker.ajp13-02.lbfactor=0 - important worker.loadbalancer.type=lb worker.loadbalancer.balanced_workers=ajp13-01, ajp13-02 Second version: worker.list=loadbalancer worker.ajp13-01.port=11009 worker.ajp13-01.host=tomcathost worker.ajp13-01.type=ajp13 worker.ajp13-01.lbfactor=0 - important worker.ajp13-02.port=11019 worker.ajp13-02.host=tomcathost worker.ajp13-02.type=ajp13 worker.ajp13-02.lbfactor=1 - important worker.loadbalancer.type=lb worker.loadbalancer.balanced_workers=ajp13-02, ajp13-01 We just try to switch the lbfactor from 1 to 0 for the first Tomcat and from 0 to 1 for the second Tomcat. after the switch we do a graceful
Re: WG: TC3.3 updating a webapp without killing sessions
Hi Hans, Thanks for your feedback, lb is high on my list as well. I hope to finish the first part of the refactoring next week, and then we can start with new features and good stuff like you mention. I'm also trying to find a way to add/remove webapps without having to restart apache. Costin On Fri, 30 Nov 2001, Hans Schmid wrote: Hi, since Costin is currently refactoring mod_jk in jakarta-tomcat-connectors I want to throw in our usage scenario. We are abusing the loadbalancing feature of mod_jk to switch tomcats on the fly in order to be able to make application updates without killing our curreent user sessions. See discussion below from tomcat-user This feature (graceful restart) was present in jserv and is still missing in mod_jk/Tomcat3.3 as far as I know. Below are references to the archive where Michael Kuz has sent a patch to decouple this feature from the lbfactor (introducing an active flag). So please keep in mind the requirement to be able to update Webapps in a farm of Tomcats without killing active sessions. Thanks, Hans -Ursprüngliche Nachricht- Von: Hans Schmid [mailto:[EMAIL PROTECTED]] Gesendet: Mittwoch, 28. November 2001 18:21 An: Tomcat Users List Betreff: AW: TC3.3 updating a webapp without killing sessions Thanks Larry, perhaps a lbfactor of 0.1 or so would do the job for us. We could probably live with 1 out of 10 sessions beeing sent to the wrong Tomcat and beeing killed if this instance shuts down. Should this be discussed in tomcat-dev ? I remember a patch from early this year which tried to fix this (check the archives) but did never make it into the release It tried to add a flag called 'active' in the worker.properties file for each worker instead of misusing the lbfactor for this. ajp13-01... lbfactor=1 active=0 and ajb13-02... lbfactor=1 active=1 see http://w6.metronet.com/~wjm/tomcat/2001/Jan/msg00102.html and http://w6.metronet.com/~wjm/tomcat/2001/Jan/msg00114.html for the patch which might be a little bit outdated -Ursprüngliche Nachricht- Von: Larry Isaacs [mailto:[EMAIL PROTECTED]] Gesendet: Mittwoch, 28. November 2001 15:00 An: 'Tomcat Users List' Betreff: RE: TC3.3 updating a webapp without killing sessions I assume the value or lbfactor is requested to be 0 because 1/lbfactor is calculated during initialization. Since this is done with doubles, it may generate an internal representation for infinity rather than a division by zero error. I don't have a complete understanding of what mod_jk does internally for loadbalancing, but your approach seems like it should work. A brief scan of the codes shows that some updates to mod_jk would be needed to insure that lbfactor=0 means only use this worker when mandated by session routing. There isn't much logging around the choice of worker. Perhaps adding some logging would help determine why requests are being routed to the lbfactor=0 Tomcat when session routing shouldn't be a factor. Hope this helps. Cheers, Larry -Original Message- From: Hans Schmid [mailto:[EMAIL PROTECTED]] Sent: Wednesday, November 28, 2001 4:25 AM To: Tomcat-User Subject: TC3.3 updating a webapp without killing sessions Hi, We try to make a workaround for the following problems: 1.) memory management 2.) application update 3.) do not kill active sessions Perhaps someone can comment on the startegy and answer some questions. Our environment: Tomcat 3.3 final with mod_jk Apache 1.3.19 on Solaris 2.7 Sparc Our problem: ever growing cache until memory runs out (clearly an application problem) plus soft updates to our application without killing actiove sessions The idea: when a certain ammount of memory is reached by the tomcat java process, start up a second Tomcat and route all new requests to the second instance while existing sessions should phase out on the first instance. If no more sessions are active on the original Tomcat, shut it down (currently we just shut it down 30 minutes after the second Tomcat started up) How to do it with mod_jk: We have two versions of a worker.properties. Before we start up our second tomcat, we switch a link to point to the other version. Both versions of the worker.property file have a loadbalancer worker defined: First version: worker.list=loadbalancer worker.ajp13-01.port=11009 worker.ajp13-01.host=tomcathost worker.ajp13-01.type=ajp13 worker.ajp13-01.lbfactor=1 - important worker.ajp13-02.port=11019 worker.ajp13-02.host=tomcathost worker.ajp13-02.type=ajp13 worker.ajp13-02.lbfactor=0 - important worker.loadbalancer.type=lb worker.loadbalancer.balanced_workers=ajp13-01, ajp13-02 Second version: worker.list=loadbalancer worker.ajp13-01.port=11009
