Name or Service not known - intermittent error in Azure

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I have a TimerTrigger which calls my own Azure Functions at a relatively high rate - a few times per second. It is not being stress tested. Every call takes just a 100ms and the purpose of the test is not a stress test.

This call to my own endpoint works about 9999 times out of 10000 but just once in a while I get the following error:

System.Net.Http.HttpRequestException: Name or service not known (app.mycustomdomain.com:443)
 ---> System.Net.Sockets.SocketException (0xFFFDFFFF): Name or service not known
   at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.ThrowException(SocketError error, CancellationToken cancellationToken)

I replaced my actual domain with "app.mycustomdomain.com" in the error message above. It is a custom domain set up to point to the Azure Function App using CNAME.

The Function App does not detect any downtime in the Azure Portal and I have Application Insights enabled and do not see any errors. So I assume the issue is somehow on the callers side and the call never actually happens.

What does this error indicate? And how can I alleviate the problem?

azure-functions azure
1 Answers

For your second question - alleviating the problem, one option would certainly be to build in retry using a library like Polly. High level you create a policy, e.g. for a simple retry:

var myPolicy = Policy
  .Handle<SomeExceptionType>()
  .Retry(3);

This would retry 3 times, to use the policy you can call a sync or async version of Execute:

await myPolicy.ExecuteAsync(async () =>
{
     //do stuff that might fail up to three times
});

More complete samples are available

This library has lots of support for other approaches, e.g. with delays, exponential delays, etc.

user_9344070
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