I'm trying to understand the output of netstat when haproxy is handling
requests waiting for the backend to finish processing. My setup is a VM
with LAN IP 192.168.10.50 hosting one haproxy and one apache httpd instance:
- apache httpd is listening on 127.0.0.1:12345 (not accessible from
outside) serving a page which needs 10 seconds to render.
- haproxy 1.8 which listens with "bind :::80 v4v6" with a backend
"server apache_backend 127.0.0.1:12345"
The relevant part of netstat output when the 2 services are running is
naturally the following:
tcp6 :::80 :::* LISTEN 14973/haproxy off
tcp 127.0.0.1:12345 0.0.0.0:* LISTEN 15020/apache2 off
I then execute "curl http://192.168.10.50/ &" 3 times from a different
host. I validate in the haproxy stats page that there are 3 concurrent
processings taking place both on the haproxy frontend section and on the
haproxy backend section (Cur: 3, Max 3).
The following groups of connections appear on netstat:
1)
tcp6 192.168.10.50:80 192.168.10.1:62942 ESTABLISHED 14973/haproxy off
tcp6 192.168.10.50:80 192.168.10.1:62941 ESTABLISHED 14973/haproxy off
tcp6 192.168.10.50:80 192.168.10.1:62940 ESTABLISHED 14973/haproxy off
2)
tcp 127.0.0.1:35154 127.0.0.1:12345 ESTABLISHED 14973/haproxy off
tcp 127.0.0.1:35156 127.0.0.1:12345 ESTABLISHED 14973/haproxy off
tcp 127.0.0.1:35158 127.0.0.1:12345 ESTABLISHED 14973/haproxy off
3)
tcp 127.0.0.1:12345 127.0.0.1:35154 ESTABLISHED 15023/apache2 keepalive
tcp 127.0.0.1:12345 127.0.0.1:35156 ESTABLISHED 15090/apache2 keepalive
tcp 127.0.0.1:12345 127.0.0.1:35158 ESTABLISHED 15099/apache2 keepalive
I understand that connections in group #1 are the ones originating from
outside the VM, initiated by the 3 parallel curl commands, which end up
on the ipv6 endpoint of haproxy, managed by its front end component. I
suppose that the haproxy backend component must then start 3 connections
to send the requests to apache. Are these connections shown in group #2
or #3? And if that is either group #2 or #3, what is the other group
supposed to be doing?
Thanks
