test.cs

class Program
    {
        static void Main(string[] args)
        {
            Run().Wait();
        }

        public static async Task Run()
        {
            var uri = new Uri("https://myUrl.com");

            var baseUri = new Uri($"{uri.Scheme}://{uri.Host}");
            var servicePoint = ServicePointManager.FindServicePoint(baseUri);

            servicePoint.ConnectionLeaseTimeout = 0;
            ServicePointManager.DnsRefreshTimeout = 1;

            using (var httpClient = new HttpClient())
            {
                httpClient.Timeout = TimeSpan.FromSeconds(5);

                // result = OK
                var dns = Dns.GetHostAddresses(uri.Host);
                var result = await httpClient.GetAsync(uri.AbsoluteUri);
                var content = await result.Content.ReadAsStringAsync();

                var test = "1231";

                // dns changed

                await Task.Delay(TimeSpan.FromSeconds(5));

                var dns1 = Dns.GetHostAddresses(uri.Host);
                var result1 = await httpClient.GetAsync(uri.AbsoluteUri);
                var content1 = await result.Content.ReadAsStringAsync();

            }
            await Task.Delay(TimeSpan.FromSeconds(5));

            var stopwatch = Stopwatch.StartNew();

            try
            {
                var reuse = new HttpClient();

                while (true)
                {
                    var dns2 = Dns.GetHostAddresses(uri.Host);
                    var httpClient = new HttpClient();
                    httpClient.Timeout = TimeSpan.FromSeconds(5);
                    var result2 = await httpClient.GetAsync(uri.AbsoluteUri);
                    var content2 = await result2.Content.ReadAsStringAsync();

                    Console.WriteLine($"Finished request dns: {uri.Host}-{dns2.First()}: {stopwatch.Elapsed}");

                    await Task.Delay(TimeSpan.FromMilliseconds(1500));
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Exception after: {stopwatch.Elapsed}");
                throw;
            }

        }
    }