The client doesn’t know anything about your request implementation, so sending that via a header doesn’t make sense, unless it’s added by some middleware that d

The client doesn’t know anything about your request implementation, so sending that via a header doesn’t make sense, unless it’s added by some middleware that does. The load balancer could keep track of how long requests for a specific path tend to take, and what servers are currently handling and use that information to be smarter about routing requests. I wouldn’t be surprised if that already exists in things like haproxy or nginx. There’s issues where people stuff data into the URL, like ids or keywords for SEO. But that’s possible to workaround.