C# ASP.NET Core - SocketException: No such host is known

Question

I am having issues which seem to be related calling a specific API asynchronously using HttpClient - the strange thing is that it doesn't happen all the time and can be solved by refreshing the page (sometimes once, sometimes multiple times).

I thought this could be a local issue but hosting on Azure produces the same results.

Raw exception details:

System.Net.Sockets.SocketException (11001): No such host is known at System.Net.Http.ConnectHelper.ConnectAsync(String host, Int32 port, CancellationToken cancellationToken)

I have checked:

• There are no limits imposed on the API
• Passing the request url in a browser returns the expected JSON result
• Refreshing the page sometimes resolves the issue

The start of the error:

The rest:

This is the method that seems to be causing the issue:

public async Task<List<MoonPhase.Phasedata>> GetPhaseDataAsync(double lat, double lng, int year)
{
    string requestUrl = "https://api.usno.navy.mil/moon/phase?year=" + year + "&coords=" + locationService.FormatCoordinates(lat, lng) + "&tz=0";

    using (var client = new HttpClient())
    {
        var content = await client.GetStringAsync(requestUrl);
        var moonPhaseObject = JsonConvert.DeserializeObject<MoonPhase.RootObject>(content, new JsonSerializerSettings
        {
            NullValueHandling = NullValueHandling.Ignore
        });

        return moonPhaseObject.PhaseData;
    }
}

Answer 1

I tested the API by attempting to access multiple times within 15 minutes (using this URI). For a minute or two it seemed to have DNS issues.

The GetStringAsync method throws an HttpRequestException exception if there are issues such as DNS failure (source). You could try catching this exception and implementing a retry mechanism if this exception is thrown.