HttpClient // Timeout // The remote name could not be resolved

Question

Hello,

The remote name could not be resolved

using (HttpClient client = new HttpClient())
{
	client.BaseAddress = new Uri(System.BaseAddress);
	client.Timeout = new TimeSpan(0, 0, System.Timeout);


	
public void Exception(Exception ex, string functionName, string url)
{
	var ext = ex.InnerException;
	while (ext != null)
	{
		ext = ext.InnerException;
	}
	throw new Exception($"Exception {functionName} = '{url}'\n \n{ex.Message}");
}

The connection must be established first. How long does that take? 10 seconds? Can I set that?

Timeout 2, when the connection is established, ask the question, no answer is sent back.

How can I solve the problem? What could be the reason? The error occurs sporadically. On average after 200 requests.

Exception InnerException='An error occurred while sending the request.'

Exception InnerException='The remote name could not be resolved: 'public.api.XXXX.com''

Is the cause on the server or on the client? I need to work out a solution, I don't have the experience. Are there any links where it can be found? The customer says all good on the server.

Who is right?

Answer 1

The error message "The remote name could not be resolved" means the domain could be be resolved to an IP which is usually a DNS issue.

See if the following guidance documentation helps.

https://learn.microsoft.com/en-us/dotnet/fundamentals/networking/http/httpclient-guidelines

Answer 2

HttpClient has one timeout parameter defaulted to 100 seconds. this is max time for a request, and included the DNS resolve, connecting to the ipaddress returned from the resolve, sending the data, the server processing the data, the server sending the response, and the client receiving the response.

"remote name can not be resolved" error means that when the client calls its DNS server, the DNS server can not find the domain defined. a DNS resolve should return in < 15 seconds. this error happens as soon as the resolve completes and is not a timeout.

Answer 3

Exception InnerException='The remote name could not be resolved: 'public.api.XXXX.com''

Try sending ping to the domain you are trying to access to see if the name resolution is properly done.

I guess actual domain is not public.api.XXXX.com. Since it is actually existing, however, avoid use it as sample in your question.

Answer 4

I provided a link with information about DNS and how it can affect HttpClient. The reference documentation also contains best practices with code examples. But, as far as I can tell you've made no changes to the code.

Below is another article explains some of the issue you might have with HttpClient depending on your environment and implementation.

https://dev.to/gkarwchan/calling-http-api-and-the-problem-of-socket-exhaustion-and-dns-rotation-555d

How can I prove this? I think so too.

Read the documentation, make some code changes depending on your implementation, and test.

Answer 5

to reach more people and their experience.

What DNS servers are you using? A simple nslookup on a name would tell you if you could reach them or not. Even if the DNS servers were not reachable, the DNS client on your pc will cache the address. "Ipconfig /displaydns" will show you the cache entries.

Here is a Powershell script that might help you. It does a nslookup every few seconds. Adjust the sleep time to suite your needs and kick it off and let it run. See if it encounters a problem at some point.

If the script encounters an error, then that would indicate that you have some general network connectivity problem.

while ($true) {
    $ms = Resolve-DnsName microsoft.com
    "{0} - Number of records = {1}" -f (get-date) , $ms.count
    start-sleep -Seconds 30
}