https://www.digitalocean.com/community/tutorials/how-to-use-haproxy-to-set-up-mysql-load-balancing--3
https://www.howtoforge.com/tutorial/how-to-setup-haproxy-as-load-balancer-for-nginx-on-centos-7/
http://lansgg.blog.51cto.com/5675165/1242674
http://blog.jobbole.com/94606/
http://www.yunweipai.com/archives/9148.html
https://www.percona.com/doc/percona-xtradb-cluster/LATEST/howtos/proxysql.html
http://fordba.com/mysql_proxysql_rw_split.html
