Azure host name resolution inside Web App

1

In the last couple of days we have some problem on our Azure Web App (S3 WebSite hosted in North Europe data center) when resolving host names.

We have created a very simple .aspx page that try to resolve google.com and sometime we receive the correct ip other times we get this error:

System.Net.Sockets.SocketException (0x80004005): No such host is known at System.Net.Dns.InternalGetHostByName(String hostName, Boolean includeIPv6) at System.Net.Dns.Resolve(String hostName) at ASP._diagnostics_dns_aspx.HostName2IP(String hostname) at ASP._diagnostics_dns_aspx.Resolve(Object sender, EventArgs e)

The same problems occurs when resolving internal azure host names (*.cloudapp.azure.com) or other host names (microsoft.com, ...).

Our suspect is that one of the instance where the app is hosted (we currently have 2 instances) have the dns resolution broken.

You can see the full aspx page code here: https://gist.github.com/davideicardi/6d3f5bf45efaeea0e2a03cba58beec5f

But basically it use the following code to resolve the requested host name:

  private string HostName2IP(string hostname)
  {
      var iphost = System.Net.Dns.GetHostEntry(hostname);
      var addresses = iphost.AddressList;
      var addressList = new System.Text.StringBuilder( );
      foreach(var address in addresses)
      {
          addressList.Append("IP Address: ");
          addressList.Append(address.ToString( ));
          addressList.Append(";");
      }
      return addressList.ToString( );
  }

Any idea? It is possible that we have broken some configuration or there is a problem in Azure?

UPDATE: If I use [System.Net.Dns]::GetHostEntry("google.com") or using nslookup inside the Kudu PowerShell console the name is always resolved. Seems to be a problem related to my website only. I have tried on both instances.

azure
domain-name-system
asked on Server Fault Aug 31, 2016 by Davide Icardi

1 Answer

0

I have an open ticket with MS that seems to confirm that it was bug on Azure side.

answered on Server Fault Sep 21, 2016 by Davide Icardi

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