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POSOA: Reasons why emulating an ESB behaviour in code, for sure, is the worse option
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copied!<p>We have an SOA based project which has been built from the ground up as a webservice layer to a well established application. </p> <pre> ClientA --> ClientB --> ESB --> Atomic Services --> Established App (DB/NAS etc) ClientC --> </pre> <p>We have several scenarios where a service provided by the ESB is composed of multiple atomic calls called in sequence with interactions, such that logically they do something like this:</p> <pre class="lang-py prettyprint-override"> def composing_service(xmlrequest): output_of_decision_service = decision_service(xmlrequest) if (output_of_decision_service.matches("foo")): xmlresult = foo_service(xmlrequest) if (output_of_decision_service.matches("bar")): xmlresult = bar_service(xmlrequest) return xmlresult </pre> <p>In fact this logic has been implemented using XSLT transforms and XPath queries build into the ESB implementation we have bought. This seems problematic to me for a few reasons:</p> <ul> <li>Developers can't test the composing services (simple functionality from business perspective) locally as the ESB implmentation is too "heavy" to be deployed locally. Overall testing is an integration activity.</li> <li>The XSLT syntax used to form these and similar control blocks are not as readable or accessible as code in a general programming language. (if ... then, else finally etc.) The XSLT has got very long and intimidating.</li> <li>In certain complex scenarios more fine grained control would be beneficial, i.e. compensating for failed calls by calling a compensating atomic service to roll back an earlier action.</li> </ul> <p>I guess after a year working on the project I feel as if the notion of decomposing the application functionality into atomic services is a good one. However I often feel as if I'd prefer to implement the composing webservices in a plain old programming language like Java. </p> <p>I guess this would look like this:</p> <pre> ClientA --> ComposingServiceA --> ClientB --> ComposingServiceB --> Atomic Services --> App ClientC --> ComposingServiceC --> </pre> <p>However, reading on here I found an unreferenced statement as follows:</p> <blockquote> emulating an ESB behaviour in code, for sure, is the worse option </blockquote> <p>Sadly this was left as a blind statement of fact (opinion) with no supporting reasons. However it got me rattled. Why could the above be true? I was ready to draft an email to our architect voicing all the concerns above, but this comment makes me wonder if I should?</p> <p>Why is emulating an ESB behaviour in code, for sure, the worst option?</p>

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