Web Application Servers Dean Jacobs BEA WebLogic

The Right Question Middleware is converging Web Application Servers = TP Monitors What new demands do the Internet and Java place on middleware?

Browsers Database Web Servers Application Server Cluster System Architecture

Web Servers Web Servers not integrated with middleware –Adds an extra server-side hop with no benefit –Obviates the front line of session concentration Web Servers integrated with middleware –Standard Web Servers must be supported –Front line session handling - load balancing and transactions - must occur in Web Server plug-ins

Relaxed Durability/Consistency Trade durability or consistency for performance: avoid disk accesses by keeping state in memory. Shopping Cart Stored as browser-session state in a servlet engine. To avoid writing backups to disk, replicate in-memory on a secondary host. Catalog Data Changes infrequently and may be briefly out-of-date. To avoid disk reads, cache on many servers in a cluster. Update anywhere and lazily flush the caches.

Fat Processes with Threads Radically different process model: 2-3 processes per host, each a logical machine Multiple resource managers per process Multiple threads accessing each resource Threads are not isolated from each other

Object Lifetime In-Memory CORBA relies on the programmer to release objects Component models (EJB) prescribe object lifetimes Programming language object models (RMI) require DGC. How can that scale?