Stop newing up HttpClient

Almost every integration I've inherited has had this somewhere in it:

public async Task<Order?> GetOrderAsync(int id)
{
    using var client = new HttpClient();
    return await client.GetFromJsonAsync<Order>($"https://api.example.com/orders/{id}");
}

It looks responsible. HttpClient is IDisposable, so we dispose it. It works on your machine, passes code review, and then falls over in production when traffic picks up.

#What goes wrong

Disposing an HttpClient also disposes its handler, which closes the underlying TCP connection. Closed connections sit in the TIME_WAIT state for a while before the operating system releases the port. Create a client per request under load and you can run out of sockets. The error is usually a SocketException that has nothing obvious to do with the code that caused it.

The common "fix" is a single static readonly HttpClient. That solves socket exhaustion but creates a quieter problem: a connection that stays open forever never sees DNS changes, so after a failover or a blue-green deployment you keep talking to the old server.

#Option 1: IHttpClientFactory (use this in ASP.NET Core)

The factory pools the handlers behind your clients and recycles them on a timer (two minutes by default). You get connection reuse and fresh DNS without managing either yourself. A typed client keeps the configuration in one place:

// Program.cs
builder.Services.AddHttpClient<OrdersClient>(client =>
{
    client.BaseAddress = new Uri("https://api.example.com/");
    client.Timeout = TimeSpan.FromSeconds(10);
});

public sealed class OrdersClient(HttpClient http)
{
    public Task<Order?> GetOrderAsync(int id) =>
        http.GetFromJsonAsync<Order>($"orders/{id}");
}

Inject OrdersClient wherever you need it. Don't dispose the HttpClient yourself; the factory owns its lifetime.

Watch out: typed clients are registered as transient. If you inject one into a singleton, the singleton holds on to one handler forever and you're back to the stale DNS problem.

#Option 2: one long-lived client with a connection lifetime

Outside of dependency injection, in a console app or an Azure Function without the DI setup, share a single client and tell its handler to recycle connections:

private static readonly HttpClient Http = new(new SocketsHttpHandler
{
    PooledConnectionLifetime = TimeSpan.FromMinutes(2)
});

#Which one to pick

#Takeaway

HttpClient is meant to be reused. Let IHttpClientFactory manage it when you have dependency injection, and set PooledConnectionLifetime when you don't.