Stanford Digital Library Testbed Development Department of Computer Science Stanford University Stanford, CA

DL Factory

A factory is a service that is responsible for creating objects. A DL Factory handles this responsibility at a UNIX process level where each object is actually a command line invocation.

Interface:

o create an object with possible criteria (like UNIX exec.)
o list possible objects (like UNIX 'dir /bin'.)
o list active objects (like UNIX 'ps'.)
o register new objects (like installing new software.)
o kill active objects (like UNIX kill.)

Description:
A DL factory is a process that creates, maintains, and destroys objects on a UNIX machine basis. Each object is a child process of the DL Factory. All functions of the factory are accessible through an ILU interface. The factory periodically checks the livelyness(using Ping) of the object and restarts the object if specified and/or necessary. It also can ask the object to periodically perform a self diagonositic if the object is known to be unstable over time (such as proxies.) The factory could also restart objects if certain constraints become invalid (such as their memory requirements growing too large for the host system, e.g. memory leaks.)

For reliablity, a crontab script can be enabled to check the livelyness of the factory and restart the factory if something goes wrong (such as the host machine crashing.)