On Thu, 11 Feb 2021 at 05:31, Victor Sudakov <[email protected]> wrote: > > Lukas Tribus wrote: > > > > On Wed, 10 Feb 2021 at 16:55, Victor Sudakov <[email protected]> wrote: > > > > > > I can even phrase my question in simpler terms. What happens if the sum > > > total of all servers' maxconns in a backend is less than the maxconn > > > value in the frontend pointing to the said backend? > > > > Queueing for "timeout queue" amount of time, and then return 503 error > > And what happens in TCP mode, after the "timeout queue" amount of time? > I suppose the TCP connection with the client is reset?
Yes, that's the only choice. > > > > > See: > > > > timeout queue > > https://cbonte.github.io/haproxy-dconv/2.2/configuration.html#4.2-timeout%20queue > > > > maxconn > > https://cbonte.github.io/haproxy-dconv/2.2/configuration.html#5.2-maxconn > > > > > > I really suggest you ignore minconn and fullconn, and focus on maxconn > > instead. The latter is a must-have (and must-understand). Really > > maxconn (global, frontend and per server ) is the single most > > important performance knob in haproxy. > > Maxconn is rather clear, especially when one is sure about two things: > > 1. A server's maxconn value is always a hard limit (notwithstanding if > there is a minconn configured for the server). Yes. > 2. Connections outnumbering the sum total of a backend's servers > maxconns are queued for the "timeout queue" amount of time and then > dropped. If, for any reason, we can't use another server with free slots, yes. > It would be nice however to understand minconn/fullconn too. If a > backend has several servers with identical minconn, maxconn and weight, > what's the point of having minconn? The load will be always distributed > evenly between all the servers notwithstanding minconn/fullconn, > correct? If the load is REALLY the same, sure. That's just never the case in real life for a number of reasons: - different load-balancing algorithms - different client behavior - session persistence - long-running TCP connections (websocket, et all) But yes, like I already mentioned, minconn/fullconn is addressing a very specific requirement that I don't think comes up very often. Lukas
