Two major issues with standard HttpClient usage in .NET:

1. Socket Exhaustion: Creating new HttpClient() per request leaves hundreds of sockets in TIME_WAIT state, starving OS network ports.
2. Stale DNS: Storing a singleton static HttpClient caches DNS indefinitely, failing when IP addresses rotate during cloud deployments.

The Fix:
Register with services.AddHttpClient() and inject IHttpClientFactory:

public class WeatherService(HttpClient client)
{
    public async Task<string> GetForecastAsync() => await client.GetStringAsync("/forecast");
}

IHttpClientFactory pools the underlying HttpMessageHandler lifetimes (default 2 minutes), rotating connections to honor DNS TTL while pooling active sockets!

IHttpClientFactory completely resolved socket exhaustion crashes in our high-traffic microservices cluster.

Also makes adding Polly retry policies, rate limiters, and circuit breakers trivial via .AddTransientHttpErrorPolicy().