Haproxy + Mysql Lost connection to MySQL server during query

I have setup a master-slave replication and added a haproxy before them. #HA-Proxy version 1.4.24 global log /dev/log local0 log /dev/log local1 notice chroot /var/lib/haproxy user haproxy group haproxy daemon defaults log global mode http option httplog option dontlognull contimeout 5000 clitimeout 50000 srvtimeout 50000 errorfile 400 /etc/haproxy/errors/400.http errorfile 403 /etc/haproxy/errors/403.http errorfile 408 /etc/haproxy/errors/408.http errorfile 500 /etc/haproxy/errors/500.http errorfile 502 /etc/haproxy/errors/502.http errorfile 503 /etc/haproxy/errors/503.http errorfile 504 /etc/haproxy/errors/504.http frontend ft_readonly_mysql mode tcp timeout client 50000 option clitcpka bind *:3308 default_backend bk_readonly_mysql backend bk_readonly_mysql mode tcp option srvtcpka timeout server 50000 option mysql-check user haproxy_check server mysql1 127.0.0.1:3306 check server mysql2 172.16.19.250:3306 check If my pymysql client connect to mysql via 3306 directly, it works well. If connect to mysql via haproxy 3308 port, it will throw OperationalError: (OperationalError) (2013, 'Lost connection to MySQL server during query') every several minutes. I doubted it was due to haproxy config so that I have added clitcpka, srvtcpka, timeout client, timeout server. But it still throws Lost connection. Update 0: mysql> show global variables like '%timeout%'; +----------------------------+----------+ | Variable_name | Value | +----------------------------+----------+ | connect_timeout | 10 | | delayed_insert_timeout | 300 | | innodb_lock_wait_timeout | 50 | | innodb_rollback_on_timeout | OFF | | interactive_timeout | 28800 | | lock_wait_timeout | 31536000 | | net_read_timeout | 30 | | net_write_timeout | 60 | | slave_net_timeout | 3600 | | wait_timeout | 28800 | +----------------------------+----------+