using System;

using System.Linq;

using System.Collections.Generic;

using System.Net;

using System.Runtime.Caching;

​

public class Program

{

    public static void Main()

    {

        var cnameDomain = "www.google.com";

        var ips = DnsTesting.GetIpsForCname(cnameDomain);

        Console.WriteLine("ips: " + String.Join(",", ips.ToList()));

        ips = DnsTesting.GetIpsForCname(cnameDomain);

        Console.WriteLine("ips: " + String.Join(",", ips.ToList()));

    }

}

​

public class DnsTesting

{

    private static MemoryCache cache = MemoryCache.Default;

    public static IPAddress[] GetIpsForCname(string cnameDomain)

    {

​

        string cacheKey = "ips_" + cnameDomain.ToLower();

​

        // Try to get data from cache

        var cachedData = cache.Get(cacheKey) as IPAddress[];

​

        if (cachedData == null)

        {

            Console.WriteLine("Cache miss! Fetching data...");

            var ttl = 300;

            try

            {

                var ip = System.Net.Dns.GetHostEntry(cnameDomain, System.Net.Sockets.AddressFamily.Unspecified);

                cachedData = ip.AddressList;

                //todo: is it possible to get the ttl from this?  Is that even necessary or can we just use 5 minutes?

            }

            catch (Exception ex)

            {

​

                cachedData = new IPAddress[] { };

            }

            // Store data in cache for 5 minutes

            CacheItemPolicy policy = new CacheItemPolicy { AbsoluteExpiration = DateTimeOffset.Now.AddSeconds(ttl) };

            cache.Add(cacheKey, cachedData, policy);

        }

        else

        {

            Console.WriteLine("Cache hit! Using cached data...");

        }

​

        return cachedData;

    }

}