HttpClients are difficult to use in C#. This class will manage them for you.

how-to-use.cs

var url = "https://api.test.com/api/test/1";
var client = HttpClientManager.Get(url);
var value = await client.GetAsync(url);

HttpClientManager.cs

// http://www.tomdupont.net/2014/11/net-45-httpclient-is-thread-safe.html
// http://www.nimaara.com/2016/11/01/beware-of-the-net-httpclient

public static class HttpClientManager
{
    private static readonly ConcurrentDictionary<string, HttpClient> clients = new ConcurrentDictionary<string, HttpClient>();
    private static readonly object lockobj = new Object();


    public static HttpClient Get(string url)
    {
        return Get(url, (uri) => new HttpClient());
    }

    public static HttpClient Get(string url, Func<Uri, HttpClient> createClient)
    {
        var numberOfClients = clients.Count;
        if (numberOfClients < 1)
        {
            ServicePointManager.DnsRefreshTimeout = (int)TimeSpan.FromMinutes(1).TotalMilliseconds;
        }

        var uri = GetBaseUri(url);
        var key = uri.Authority;
        if (!clients.TryGetValue(key, out var client))
        {
            lock (lockobj)
            {
                if (!clients.TryGetValue(key, out client))
                {
                    client = clients.GetOrAdd(key, createClient(uri));
                    ServicePointManager.FindServicePoint(uri).ConnectionLeaseTimeout = (int)TimeSpan.FromMinutes(1).TotalMilliseconds;
                }
            }

        }

        return client;
    }


    private static Uri GetBaseUri(string url)
    {
        var wholeUri = new Uri(url);
        var baseString = $"{wholeUri.Scheme}://{wholeUri.Authority}";
        var baseUri = new Uri(baseString);
        return baseUri;
    }
}