Yes. In each tomcat, you will need in server.xml <Engine jvmRoute="someUniqueTomcatId" ...>
Then each uniqueTomcatId will need to be in workers.properties (or whatever config file you make apache use). Then all the 'uniqueTomcatId' workers sit behind a loadbalancer worker also defined in worker.properties.
The drawback is if a tomcat goes down, then you lose the session in a user tries to go to that instance. Luckily you can persist all sessions to a file and hope for a quick restart to minimize the amout of damage. Otherwise, there are 2 workarounds:
- Persist session data in a database
- Use the clustring facilities. But in tomcat4 they are more or less experimental. In tomcat5 - they will be MUCH better.
The faq has a lot of links to other sites and to the docs: http://jakarta.apache.org/tomcat/faq/connectors.html
-Tim
Dan Hart wrote:
Please forgive my ignorance in this matter and the inherant rudeness in asking a question moments after subscribing to this list.
The short question: Is it possible to maintain persistant connections across a line of front-end apache 1.3 linux boxen? The goal is high availability. If possible, please point me in the right direction of finding documentation on this ability.
Diagram: ========
Hardware LB Level: BigIP (Redundant, of course) | +----+----+----+----+----+--... | | | | | | ... Webserver Level: webA webB webC webD webE webF ... (Apache + mod_jk) | | | | | | ... +----+----+----+----+----+----+--... | | | | | | | ... Tomcat Level: tc1 tc2 tc3 tc4 tc5 tc6 tc7 ... (On Solaris 8) | | | | | | | ... +----+----+----+----+----+----+--... Database Level: | Database (Redundant, of course)
Details: ========
I understand on a basic level how the mod_jk connector works, mainly from documentation found in the worker's HOWTO. To quote:
* sticky_session specifies whether requests with SESSION ID's should be routed back to the same Tomcat worker. If sticky_session is an int and is not 0 it is set to JK_TRUE and sessions are sticky, otherwise sticky_session is set to false. Set sticky_session to JK_FALSE when Tomcat is using a Session Manager which can persist session data across multiple instances of Tomcat. By default sticky_session is set to JK_TRUE.
This appears to refer to a single apache instance. It also seems to be enabled by default, which would explain the difficulty in finding documentation on it ;) From past experience with mod_jserv, I know I could do this setup using ApJServRoute directives (assuming these were the same across all systems, of course).
So is this possible with mod_jk? My assumption is that "Yes, of course this is possible you twat and is enabled by default even!" however such answers tend to go poorly at higher levels of management. So a piece of official documentation showing this would be highly appreciated.
Thanks!
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