Connecting to multiple clusters using WAR file

Question

I am trying to connect to multiple clusters by creating separate WAR(web archive) files through Apache tomcat.
My intention is to have each 'war' act as a node to a separate cluster. I started with the 'jmx-console' example available on the Tangosol website.
So, my understanding is that even though all the war files are loaded in the same JVM (tomcat), since each of these war's has its own classloader, we can have multiple tangosol ndoes from the same JVM.
So I have two basic questions:
*) If I use system.setProperty("tangosol.coherence.override", myOverrideFile-x) in the class loader of each WAR, can I have the nodes connect to different clusters. is'nt the System.setProperty() setting the property on the JVM? If so, how can multiple classloaders running in the same JVM connect to different clusters?
*) Where should I place config/override xml files under the tomcat directory structure for it to be accesible to the class loader.

Answer 1

Hi sumax,
Thanks for your response Robert,
Maybe I did not understand your solution fully, I
thought your idea mostly talks about how to configure
the override files, and not how to configure the
individual nodes to use different override files.
That part is taken care of by the fact, that each war file loads the tangosol-coherence-override.xml from its own WEB-INF/classes directory.
Classloading from a web app in Tomcat resolves classpath classes/resources in the following order:
1. java.* and javax.* and com.sun.* packages are loaded from the system classloader. This, I believe, cannot be circumvented on a Sun JVM with a classloader extending a JDK classloader class.
2. Reloadable JSP classloader (loads servlet classes generated from JSP pages). This is webapp specific, each webapp sees its own generated servlet classes.
3. Reloadable Webapp classloader (loads from WEB-INF/classes and WEB-INF/lib of the war). This is webapp specific, each webapp sees its own WEB-INF/classes and WEB-INF/lib.
4. Common classloader (loads from ${TOMCAT_HOME}/common/classes and ${TOMCAT_HOME}/common/lib). This is used by all webapps and the Tomcat container itself. You should not put anything here, except for libraries for resource drivers, etc. JDBC drivers or anything which needs to be published in the JNDI server in a non-application-specific way.
5. Shared classloader (loads from ${TOMCAT_HOME}/shared/classes and ${TOMCAT_HOME}/shared/lib). This is shared between all webapps but not by the Tomcat container. You can put libraries here with which you want to communicate between webapps. Any singletons in classes in this classloader will be shared between webapps. A place for configuration files which are shared or if they have the application name in their filenames (so that they are not accidentally used by another application).
The question still lingering in my mind is:
How do I tell the classloader which override file to
load.
A tangosol-coherence-override.xml with different content should be put in the WEB-INF/classes directory of each war file. Each of those files will be loaded only by its containing webapp. This filename is defined in the deployment-mode-specific override files in coherence.jar or tangosol.jar (I don't remember which, off my head) which all chain to this same tangosol-coherence-override.xml file.
That override file can contain all your overrides, if you do not want to change those between restarts, or it can chain with its xml-override attribute (as shown in the example) to another file with the application name in its filename.
This chaining allows each webapp to refer to a differently named override file, so all those override files can be put into shared/classes folder. The uniquely named override file in shared/classes allows you to change the override configuration between restarts.
As for cluster address and port, you can specify those in any of the override files.
The full chaining path is the following (if you used the tangosol-coherence-override.xml example in my first reply):
tangosol-coherence.xml -> tangosol-coherence-prod.xml -> tangosol-coherence.xml (you provide this file in your webapp WEB-INF/classes) -> tangosol-coherence-override-warfilename.xml (you provide this file in the ${TOMCAT_HOME}/shared/classes)
I hope this makes it clear.
Best regards,
Robert