Transcript Dean Jacobs: Web Application Servers

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?
System Architecture
Database
Browsers
Web Servers
Application Server
Cluster
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briefly out-of-date.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?