From
an exploiter??™s perspective, the service rarely fails. At most, there is a slight slowdown in
performance, which is undesirable, but better than failing altogether. Adding a proxy layer
between the requestor and the actual data access method lets the application short-circuit a
potentially grave situation early, preserving the rest of the application.
Another example includes a typical dependency on a database or LDAP directory. BluePages
provides both directory lookup and free text search. The truth is that the free text
search can provide similar search results to that of the directory query, but the results are
not exactly the same. Based on the previous example, it is easy to imagine the monitoring
Approaches to Bu ld ng H gh Performance Web Appl cat ons
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system provided in the application. The difference here is that if there is a problem with
the LDAP resource, the current deployment has no effective way for failover. Instead of
simply sending an error or notifying the user that the LDAP servers are causing a problem
(not exactly something the average user understands), a subsequent query is automatically
performed using the free text search.
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