Anton Tagunov wrote:
Hello Shash!
Please give a several day allowance to try to understand it. Not quite possible on the first pass :-)
You are allowed as much time as you need, until the test starts, and it'll be a closed-book test :-)
> Why brainstorming this, could you please tell me additionally, > how are the Servlet Container and the Keel server related? > > Do they live in the same JVM? > > - Anton
The servlet container and Keel-server can certainly be in the same JVM.
There are several "transports" between the Keel client (in this case a webapp) and the Keel server: direct (same JVM), JMS (openJMS or JBossMQ) and SOAP (Axis). Even in the same-VM version, we strived to keep the webapp classloader separate from the Keel-server, based on prior experiences with Xerces and Tomcat conflicts. So, in the same-VM deployment, the webapp and Keel-server exchange serialized request/response pairs over a pair of "Channels" from Doug Lea's concurrent package. The two sides of each Channel have separate classloaders.
This separation between the servlet-container/Keel-client and Keel-server is an important piece of the Keel architecture. Besides scalability, this allows development against the same-VM version and deployment to the distributed version with absolutely no changes.
As it stands today, you can scale the deployments in the following ways:
- single webapp, same-JVM Keel server - single webapp, distributed Keel server (with JMS or Axis) - multiple webapps (single JVM), distributed Keel server - multiple webapps (multiple JVMs), distributed Keel server
And the most exciting piece we are working on:
- multiple webapps (multiple JVMs) to cluster of Keel servers (with context sharing). This will allow failover and load-balancing. The next piece along the same lines will be integrating Keel's persistence layer with C-JDBC (c-jdbc.objectweb.org) to allow another tier of distribution and scalability.
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