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POAzure web role trouble accessing external web service
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  1. POAzure web role trouble accessing external web service
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    copied!<p>I have an Azure web role that accesses an external WCF based SOAP web service (port 80) for various bits of data. The response from this service is highly erratic. I routinely get the following error.</p> <blockquote> <p>There was no endpoint listening at <a href="http://www.myexternalservice.com/service.svc" rel="nofollow">http://www.myexternalservice.com/service.svc</a> that could accept the message. This is often caused by an incorrect address or SOAP action.</p> </blockquote> <p>To isolate the problem I created a simple console app to repetitively call this service in 1 second intervals and log all responses.</p> <pre><code> using (var svc = new MyExternalService()) { stopwatch.Start(); var response = svc.CallService(); stopwatch.Stop(); Log(response, stopwatch.ElapsedMilliseconds); } </code></pre> <p>If I RDP to one of my Azure web instances and run this app it takes 10 to 20 attempts before it gets a valid response from the external service. These first attempts are always accompanied by the above error. After this "warm up period" it runs fine. If I stop the app and then immediately restart, it has to go back through the same "warm up" period.</p> <p><strong>However</strong>, if I run this same app from any other machine I receive valid responses immediately. I have run this logger app on servers running in multiple data centers (non Azure), desktops on different networks, etc... These test runs are always very stable.</p> <p>I am not sure why this service would react this way in the Azure environment. Unfortunately, for the short term I am forced to call this service but my users cannot tolerate this inconsistency.</p> <p>A capture of network traffic on the Azure server indicates a large number of <strong>SynReTransmit</strong>'s in 10 second intervals during the same time I experience the connection errors. Once the "warm up" is complete the SynReTransmit's no longer occur.</p>
 

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