"Publication - is the Auction Of the Mind of Man" Emily Dickinson
Wednesday, July 25, 2012

In order to build robust cloud applications, a client that calls a service has to handle four scenarios:

Complete Success
Partial Success (Success with conditions)
Transient Failure
Resource Failure

A partial success occurs when a service only accomplishes part of a requested task. This might be a query where you ask for the last 100 transactions, and only the last 50 are returned. Or the service only creates an order entry, but does not submit the order. Usually a reason is supplied with the partial success. Based on that reason the client has to decide what to do next.

Transient failures occur when some resource (like a network connection) is temporarily unavailable. You might see this as a timeout, or some sort of error information indicating what occurred. As discussed in a previous post , continually retrying to connect to a transient resource impedes scalability because resources a being held on to while the retries are occurring. Better to retry a few times and if you cannot access the resource, treat it as a complete failure.

With failure, you might try another strategy before you treat the resource access as a failure. You might relax some conditions, and then achieve partial success. You might access another resource that might be able to accomplish the same task (say obtain a credit rating) albeit at greater cost. In any case all failures should be reported to the client. You can summarize this responsibility in this diagram:

Bill Wilder helped me formulate these thoughts.

7/25/2012 6:25:02 PM (Eastern Standard Time, UTC-05:00) | Comments [0] | All | Cloud Computing | Microsoft .NET | SOA | Software Development#
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