HAProxy logs to a syslog facility local0, via a socket connection. By default, your syslog configuration probably doesn’t accept socket connections, and doesn’t have a local0 facility, so you have no HAProxy log. If you want it, configure syslog to accept TCP connections by adding -r to syslogd parameters.

RedHat/CentOS: edit the value of SYSLOGD_OPTIONS in /etc/sysconfig/syslog 
SYSLOGD_OPTIONS="-m 0 -r" 
 
Debian/Ubuntu: edit the value of SYSLOGD in /etc/default/syslogd 
SYSLOGD="-r" 
 
Then set up syslog facility local0 and direct it to file /var/log/haproxy.log by adding this line to /etc/syslog.conf: 
 
local0.* /var/log/haproxy.log 
 
Restart syslog service: 
 
service syslog restart

haproxy + mysql配置文件

global 
    chroot      /var/lib/haproxy 
    pidfile     /var/run/haproxy.pid 
    maxconn     4096 
    user        haproxy 
    group       haproxy 
    daemon 
 
#--------------------------------------------------------------------- 
# common defaults that all the 'listen' and 'backend' sections will  
# use if not designated in their block 
#--------------------------------------------------------------------- 
defaults 
    mode        http 
    log         global 
    option      dontlognull 
    option      httplog 
    option      redispatch 
    timeout connect 10000 # default 10 second time out if a backend is not found 
    timeout client 300000 
    timeout server 300000 
    maxconn     60000 
    retries     3 
    log 127.0.0.1 local3 
 
listen admin_stats 192.168.1.113:8000 
     mode               http 
     stats uri          /dbs 
     stats realm        Global\ statistics 
#     stats auth                admin:123456 
 
listen proxy-mysql 0.0.0.0:3306 
     mode tcp 
     balance roundrobin 
     option httpchk OPTIONS * HTTP/1.1\r\nHost:\ www 
     server hd03 10.50.12.3:3306 weight 1 check port 6033 inter 1s rise 2 fall 2 
     server hd05 10.50.12.5:3306 weight 1 check port 6033 inter 1s rise 2 fall 2 
     server hd06 10.50.12.6:3306 weight 1 check port 6033 inter 1s rise 2 fall 2 
     option tcpka