Before I describe my problem, here is the configuration of my haproxy :

Public IP : 202.X.X.X
LB ip : 10.100.3.30
[root@VM-LB1 ~]# cat /etc/haproxy/haproxy.cfg
global
log /dev/log local0 debug
maxconn 4096
#chroot /usr/share/haproxy
pidfile /var/run/haproxy.pid
uid 99
gid 99
daemon
debug
#quiet
stats socket /var/run/haproxy.stat

defaults
log global
retries 3
maxconn 1000
contimeout 5000
clitimeout 86400000
srvtimeout 86400000

listen stats :7777
mode http
stats enable
stats hide-version
stats uri /haproxy
stats auth admin:123456
stats realm HAProxy\ Statistics
stats admin if TRUE

frontend CAS-WEB
mode tcp
bind :80,:443
default_backend cas-web-servers
option tcplog

frontend CAS-pop3
mode tcp
bind :110,:993,:995
default_backend CAS-pop3-servers
option tcplog

frontend HT-SMTP
mode tcp
bind :25,:587
default_backend ht-servers

backend cas-web-servers
balance leastconn
option redispatch
option abortonclose
stick on src
stick-table type ip size 10240k expire 240m
#option ssl-hello-chk
option httpchk HEAD / HTTP/1.0
server cas1 10.200.1.32 check port 443 check-ssl inter 5000 rise 2 fall 2
server cas2 10.200.1.42 check port 443 check-ssl inter 5000 rise 2 fall 2

backend CAS-pop3-servers
stick-table type ip size 10240k expire 60m
stick on src
option redispatch
option abortonclose
balance leastconn
server cas1 10.200.1.42 weight 1 check port 110 inter 2000 rise 2 fall 3 on-marked-down shutdown-sessions

backend ht-servers
option redispatch
option abortonclose
balance leastconn
server ht1 10.200.1.33 check port 25 inter 5000 rise 2 fall 2
server ht2 10.200.1.43 check port 25 inter 5000 rise 2 fall 2


Problem :

I have 2 backend servers running Exchange OWA. connection speed is excellent if 10.200.1.32 is up. If it is down, traffic will point to 10.200.1.42 and it will start to crawl. OWA will be VERY slow, Outlook(connect using outlook anywhere technology, which is also dependent on 443) will also take forever to connect.

But, I if nat the public ip directly to 10.200.1.42(meaning without going through haproxy), OWA and Outlook can load very fast!.

Question is :

why 10.200.1.32 is fast and why 10.200.1.42 is slow? something wrong with my haproxy config? and why there is not problem if i NAT directly to 10.200.1.42

Thanks in advance.

It could be related to health check failures?

I would personally check the logs or HAProxy stats page and look for error and dwntime.

Hope that helps.