As disadvantages of the proposed solution, we should mention that it will not be usable
for every Web application. Particularly, only those applications designed with replicable
actions (see section Replicable Actions) could benefit from this high-availability support.
Moreover, Web applications should exhibit deterministic behavior (they should be state
machine servers).
Figure 3. Web application
Web
server
Database
Applications
Documents
HTTP
Gald??mez
Copyright ?© 2007, Idea Group Inc. Copying or distributing in print or electronic forms without written permission
of Idea Group Inc. is prohibited.
For instance, the proposed architecture could not be used to enhance availability of corporate
systems that access non-replicated systems, components which are difficult to replicate such
as complex legacy systems or remote systems managed by different organizations.
As a rule of thumb, automatic replication will only work for complete and self-contained
systems which behave deterministically.
However, if systems to be replicated access remote systems, but interfaces to access them
are clear, it should be interesting to assess whether simple proxy software modules could
suffice to convert the system into a self-contained one.
Pages:
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552