Maxconn causing close_wait

[lukastribus]

@vignesh-sp

We have configured the lb to take only maximum of 100 conncurr connections at a time by setting 100 as maxconn value.

I start hitting the lb with 120 connections, now I expect to see haproxy to accept 100 connections and rest of the connections should be given with 503.

No, that is not how it works.

If you set maxconn 100 on the frontend, haproxy will stop accepting new sockets from the kernel and they will queue up on the OS side.

A 503 can only be send with an established and accepted TCP connection. Not accepting TCP connection means not being able to send traffic to the other side.

If you configure maxconn 100 for a backend server on the other hand, then haproxy will queue the requests and when timeout queue hits it would emit appropriate HTTP responses (IF and only if the frontend maxconn configuration is larger than that, otherwise requests are not accepted there anyway).

@vignesh-sp

But this connection in haproxy stays for a longer time, until I stop the traffic to the frontend.

So it’s not a leak. Does haproxy use 100% of the CPU during this benchmark?