https://cbonte.github.io/haproxy-dconv/configuration-1.5.html#4-option%20tcp-check
https://www.haproxy.com/documentation/hapee/1-5r2/traffic-management/health-checking/
https://www.kancloud.cn/kancloud/openresty-best-practices/50428
https://www.haproxy.com/documentation/aloha/7-0/haproxy/healthchecks/
https://cbonte.github.io/haproxy-dconv/configuration-1.5.html#4-option%20tcp-check