Most devs know not to use new HttpClient(),
but they forget the REAL killer: DNS caching.
Containers change DNS → HttpClient reuses stale DNS forever.
✔ Fix
Use SocketsHttpHandler.PooledConnectionIdleTimeout:
builder.Services.AddHttpClient("api")
.ConfigurePrimaryHttpMessageHandler(() =>
new SocketsHttpHandler
{
PooledConnectionIdleTimeout = TimeSpan.FromMinutes(2)
});
Prevents DNS poisoning.