HAProxy Health Check

https://www.haproxy.com/documentation/aloha/7-0/haproxy/healthchecks/#checking-a-http-service

Squid - caching HTTP, HTTPS, FTP, and more

http://www.squid-cache.org

Debugging

https://mitmproxy.org/
allows traffic flows to be intercepted, inspected, modified and replayed.

SNI

Server Name Indication (SNI) is an extension to the TLS
allows a server to present multiple certificates on the same IP address and TCP port number
Wiki: https://en.wikipedia.org/wiki/Server_Name_Indication

Varnish

https://hub.docker.com/r/centos/varnish-4-centos7/
https://access.redhat.com/containers/?tab=overview#/search/varnish

Real IP

https://support.cloudflare.com/hc/en-us/articles/200170986

https://support.cloudflare.com/hc/en-us/articles/200170706-How-do-I-restore-original-visitor-IP-with-Nginx-

Google Analytics

https://analytics.google.com/analytics/web/#/.../admin/property/settings

all links for which you want enhanced click attribution should have an ID attribute